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Meeting In Memory Of
Piero Elter
the relationships between northern apennine
and western alps:
state of the art fifty years after the
“ruga del bracco”
Abstract Volume
volume Editors:
Michele MARRONI, Giancarlo MOLLI, Luca PANDOLFI and Piero
PERTUSATI - Dipartimento di Scienze della Terra, Università di Pisa
Pisa, June 26-27, 2014
Franco Marco ELTER - Dipartimento di Scienze della Terra
dell’Ambiente e della Vita, Università di Genova
MEETING IN MEMORY OF PIERO ELTER
the relationships between northern
apennine and western alps:
state of the art fifty years after the
“ruga del bracco”
Pisa, June 26-27, 2014
ABSTRACT VOLUME
volume Editors:
Michele MARRONI, Giancarlo MOLLI, Luca PANDOLFI and Piero
PERTUSATI - Dipartimento di Scienze della Terra, Università di Pisa
Franco Marco ELTER - Dipartimento di Scienze della Terra
dell’Ambiente e della Vita, Università di Genova
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Collision, Collapse and Delamination:
The making of the Alps-Apennine connection
Andrea Argnani
ISMAR-CNR, Bologna, Italy
The relationship between the Alps and Apennines represents a critical issue of the Italian geology and has major relevance on the geological evolution of the Central
Mediterranean region (e.g., Elter and Pertusati, 1973;
Argnani, 2009).
The long term evolution of the Alps-Apennine connection can be related to the Mesozoic palaeogeography of the region (Fig. 1A). The collision of the Adria
promontory played a key role in imposing the SW-ward
extent of the Alpine belt and in locating of collapse of
the Alpine belt during the progressive NE-ward shift of
the promontory along the plate boundary. The NE-ward
shift of continental collision that results from kinematic reconstruction represents a viable alternative to the
occurrence of a microcontinent located between Africa and Eurasia (e.g., Molli and Malavieille, 2011), for
which there is little room in geological reconstructions
(Argnani, 2012; van Hinsbergen et al., 2014).
The collapse of the Alpine belt was promoted by NEward motion of Adria relative to Eurasia, that placed
the orogen above an Appennine oceanic subduction
(Fig. 1B). A major effect of this change in polarity of
subduction was to disactivate the collisional regime
since late Eocene, as illustrated in the geological evolution of Alpine Corsica. A similar setting is currently
present offshore north Taiwan, as the colliding Luzon
volcanic arc shifted south-ward along the plate boundary. The plate kinematic evolution of the last 10 Myr
or so of the system that encompasses the collision of
the Luzon arc with Eurasia in Taiwan, passing to the
north to the retreating subduction of the Philippine Sea
plate, represents the best current analogue of the Oligocene-Miocene Alps-Apennine relationships (Argnani,
2009, 2012).
The post-collisional extension of the Alpine belt of Corsica occurred before the rollback of the Adriatic slab,
and was driven by gravity during the change from continent collision to oceanic subduction with opposite polarity. As a result of this kinematic evolution, the region
comprised between the Alpine and Apennine belts, and
now mostly located in the northern Tyrrhenian Sea, is
floored by orogenic units (Argnani, 2009).
Within the reduced convergence that followed the continental collision of Adria, the oceanic lithosphere of
the Alpine Tethys was subject to sinking and rollback,
creating the backarc opening of the Balearic basin, and
starting the related calc-alkaline volcanism. The consuption of the African (Adriatic) oceanic lithosphere
was completed during the rotation of Corsica-Sardinia,
leading to a soft-collsiion with the Adriatic continental
margin. The subsequent evolution of the Apennine orogen was controlled by continental delamination of the
Adriatic lithosphere (Argnani, 2002). The most notable effect of this last stage evolution has been the onset of the Tuscan magmatism (Serri et al., 1993). The
east-ward extent of the Tuscan magmatism can be taken
as conservatively indicating the hinge of the subducted
Adriatic lithosphere. An interesting implication concerns the structure of the Adriatic lithospheric mantle.
It is known that the SKS mantle anisotropy in Tuscany describes a pattern of NW-trending fast axes, which
contrasts with the supposed retreat of the Adriatic slab
(Salimbeni et al., 2013). To account for this “anomalous” pattern it has been suggested that it is related to
toroidal mantle flow, that should bring in material from
the mantle below the Adriatic slab, entering counterclock-wise around the northern tip of the Adriatic slab.
The width of the area with northwest-trending fast axes,
however, seems exceedingly large, and the lack of fast
directions with retreating (northeast-ward) signal is a
bit intriguing, as slab retreat is suggested as driving the
mantle flow. An alternative interpretation is here proposed, which considers the mantle fabric related to the
Mesozoic extension. The axes of fast directions, in fact,
result sub-parallel to the trend of the main fracture zone
(Adria Fracture Zone; Fig. 1A) that bounds to the west
the Adria promontory, and that is inferred to link the
two subduction zones with opposite polarity of the Alps
and Apennines (Argnani et al., 2006; Argnani, 2012).
3
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Figure 1. Frames of tentative palaeogeographic reconstruction. A) Santonian (83 Ma). The Adria continental promontory
has a large oceanic embayment on its western side. Continental collision s.s. was limited to the Alps and Corsica, and did
not extend to the SW, where an Apennine vergent oceanic subduction was present. The polarity of subduction changes across
the Adria Fracture Zone . B) Chattian (25.5 Ma). The Apennine subduction has progressively taken over in Alpine Corsica,
as Adria moves N-ward, leaving an inactive subduction. The progressive substitution from Alpine to Apennine subduction
caused a sector of the Alpine belt to collapse gravitationally (gray field).
REFERENCES
- Argnani, A. (2002). The Northern Apennines and the
Kinematics of Africa–Europe convergence. Boll. Soc.
Geol. It., 1, 47–60 (Vol. Spec).
- Argnani, A. (2009). Plate tectonics and the boundary between Alps and Apennines. It. J. Earth Sci., 128,
317–330.
- Argnani, A. (2012). Plate motion and the evolution of
Alpine Corsica and Northern Apennines. Tectonoph.,
579, 207–219.
- Argnani, A., Fontana, D., Stefani, C., Zuffa, G.G.
(2006). Palaeogeography of the Upper Cretaceous–Eocene carbonate turbidites of the Northern Apennines
from provenance studies. In: Moratti, G., Chalouan,
A. (Eds.), Tectonics of the Western Mediterranean and
North Africa: Geological Society, London, Special Publications, 262, pp. 259–275.
- Elter, P. & Pertusati, P. (1973). Considerazioni sul limite Alpi-Appennino e sulle sue relazioni con l’arco delle
Alpi Occidentali. Memorie della Società Geoligica Italiana 12, 359–375.
- Molli, G. & Malavieille, J. (2011). Orogenic processes
and the Corsica/Apennines geodynamic evolution: insights from Taiwan. Int. J. Earth Sci., 100, 1207–1224.
- Salimbeni, S., Pondrelli, S. & Margheriti, L. (2013).
Hints on the deformation penetration induced by subductions and collision processes: Seismic anisotropy
beneath the Adria region (Central Mediterranean). J.
Geoph. Res., 118, 1–13, doi:10.1002/2013JB010253.
- Serri, G., Innocenti, F. & Manetti, P. (1993). Geochemical and petrological evidence of the subduction of delaminated Adriatic continental lithosphere in the genesis
of the Neogene-Quaternary magmatism of central Italy:
Tectonoph., 223, p. 117–147.
- van Hinsbergen, D.J.J, Vissers, R.L.M. & Spakman,
W. (2014). Origin and consequences of western Mediterranean subduction, rollback, and slab segmentation.
Tectonics, doi: 10.1002/2013TC003349
4
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
A new stratigraphic and tectonic model of the South eastern Monte Antola Unit and its relationship with the Monte Gottero Unit (eastern Liguria)
Pietro Balbi, Franco Marco Elter, Egidio Armadillo and Michele Piazza
DISTAV - Department of Earth Science, Environment and Life, University of Genova, Italy
Within the complex and frequently discussed junction
between the Alps and the Apennines, two cretaceous
turbiditic Tectonic Units outcrop: M. Antola (UA) and
M. Gottero (UG). The study area is located in eastren Liguria (Northern Italy) between the cities of Genova and
Chiavari, where the Monte Antola Unit (Upper Campanian – Paleocene, Corsi et al., 2001), the upper tectonic
unit of the Ligurian stack, overlays the Internal Ligurian
Units, particularly the Monte Gottero Unit (Valanginian – Paleocene, Marroni, 1991). The aim of this work
is to present new stratigraphic data on the UA and to
discuss its stratigraphic and tectonic relationships with
the UG in the area of the eastern Fontanabuona Valley
(GE). These two units are made up of upper Cretaceous
calcareous and silicoclastic Flysch, and they show an
intense pre-Oligocene brittle-ductile deformation followed by a mainly fragile deformation. In the study
area the UA is usually considered to be very thin (up to
about 200 m) and thrusted over the basal complex of the
UG (Lavagna shales and Manganesiferi shales). Recent
literature (e.g. Marroni et al., 2004) describes an about
N100° thrust fault in the southern side of Fontanabuona
Valley, that tectonically displaces the Antola Formation
directly onto the UG with a top-to-NE movement, but an
accurate and detailed field survey doesn’t confirm this
interpretation. Evidences of stratigraphic contact between the Calcari del M. Antola Formation and the pelagic rocks underneath suggest a new stratigraphy of the
UA and a slightly northward shift of the thrust surface. It
is therefore possible to draw a new and more complete
lithostratigraphy of the Unit in this area that can help to
reconstruct its Cretaceous position.
The above-mentioned pelagic rocks lie at the base of the
UA and are here informally named respectively from the
bottom to the top “argilloscisti di Maxena formation”
and “Sanguineto member”. These rocks show interesting lithological and chronological analogies with some
basal formations of the UG, respectively with the “Scisti
Ardesiaci di M. Verzi Formation” and the “Scisti Manganesiferi Formation”.
It is interesting to underline the peculiar shape as drawn
in the map of this part of the UA, NW-SE oriented while
the rest of the Unit is NNE-SSW oriented. This fits nice-
ly with the very well known differences in orientation of
the main fold axis of the south eastern UA relatively to
the main body of the Unit (Marini, 1981), being NW-SE
oriented while the others trend NNE-SSW.
Within this new scenery, we propose that the eastern
part of the UA is certainly recognizable as a Cretaceous
Flysch, but it shows important stratigraphic differences
from the proper UA.
In the study area it is possible to state that the Gottero and
Antola Units have an approximately coeval and partially
common sedimentary history, followed by a similar succession of deformational events (mainly compressional,
known as the “Ligurian Deformational Phases”) during
which the UA overthrusted the UG with a top to N-NE
movement. During these events, because of the thrust
surface, the UA got antiformally folded while the UG
got synformally folded and experienced an epizonale
metamorphism (Bonazzi et Al. 1987).
REFERENCES
- Bonazzi A., Cortesogno L., Galbiati B., Reinhardt
M., Salvioli Mariani E., Vernia L (1987). Nuovi dati
sul metamorfismo di basso grado nelle unità liguridi
interne e loro possibile significato nell’evoluzione
strutturale dell’Appennino settentrionale - Acta.
Nat. Ateneo Parmense, 23, 17-47.
- Corsi B., Elter F.M., Giammarino S. (2001).
Structural fabric of the Antola Unit (Riviera di Levante, Italy) and implications for its alpine versus
apennine origin. Ofioliti, 26 (1), 1-8.
- Marini M. (1981). Analisi geologico- strutturale
ed interpretazione paleogeografica e tettogenica dei
calcari del M. Antola (Appennino Ligure). – Ofioliti, 6 (1), 119-150.
- Marroni M., 1991. Deformation history of the Mt.
Gottero Unit (Internal Ligurid Units, Northern Appennines). Boll. Soc. Geol. It., 110, 727-736.
- Marroni M., Meneghini F., Pandolfi L (2004). From
accretion to exhumation in a fossil accretionary
wedge: a case History from Gottero Unit (Northern
Appennines, Italy). Geodinamica Acta 17, 41-53.
5
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Broken and dismembered formations in the Monviso
Meta-ophiolite Complex (Western Alps)
Gianni Balestro(1), Andrea Festa(1), Paola Tartarotti(2)
(1) Dipartimento di Scienze della Terra, Università di Torino, Italy
(2) Dipartimento di Scienze della Terra, Università di Milano, Italy
The Monviso Meta-ophiolite Complex (axial sector of
the Western Alps) represents a eclogitized remnant of
the Ligurian-Piedmont oceanic lithosphere, tectonically superposed on the Dora Maira Unit (i.e. the European continental margin), and tectonically overlain by
the Queyras Schistes Lustrés (i.e. the fossil accretionary
wedge) (CASTELLI et alii, 2014, and references therein). The Monviso Meta-ophiolite Complex consists of
different W-dipping tectonic units that are currently
alternatively interpreted as i) a pile of imbricated tectonostratigraphic units (LOMBARDO et alii, 1978),
ii) a fossilized serpentinite subduction channel wherein ophiolite “blocks” were tectonically and chaotically
juxtaposed (GUILLOT et alii, 2004), and iii) an original
almost continuous portion of oceanic litosphere subducted to 80 km depth and deformed by eclogite-facies
shear zones (ANGIBOUST et alii, 2011). These tectonic
units consist of serpentinite, Mg-Al and Fe-Ti metagabbros, basalt-derived metabasite and different type of
metasediments, and were affected by three main deformation phases corresponding to i) a first subduction-related deformation phase (D1), represented by an early
eclogitic foliation (S1) overprinting primary surfaces, ii)
a subsequent collision-related deformation (D2), resulting in non-cylindrical W-verging folds that developed
the blueschist- to greenschist-facies regional foliation
(S2), and iii) a late-metamorphic deformation (D3) developing SW- and NE-dipping conjugate transtensional
shear zones (BALESTRO ET ALII, in press).
The lower part of the northern Monviso Meta-Ophiolite
Complex (i.e. the Pellice Valley; BALESTRO et alii,
2011) particularly consists of serpentinites and metagabbros covered by a quite heterogeneous metasedimentary succession, made up of calcschist, micaschist and
quartzite, metabreccia and metasandstone of gabbroic
composition, and carbonate-bearing mafic schist. This
metasedimentary succession is peculiarly characterized
by the occurrence of block in matrix structures (sensu FESTA et alii, 2010), corresponding to broken and
dismembered formations. The latters differ each other
in the degree of stratal disruption (from dismembered
interbeds to isolated blocks) of the massive metabreccia and metasandstone horizons that are enveloped in a
matrix of calcschist, micaschist and mafic schist. Both
broken and dismembered formations are the product of
polyphasic deformation related to the superposition of
D1, D2 and D3 structures. During the D2 deformation,
the S1-parallel metasedimentary succession was affected by progressive layer-parallel extension, boudinage
and non-cylindrical folding, that induced significant
stratal disruption, shearing and transposition of rootless
fold hinges. Subsequent D3 deformation favored mixing processes by dissecting the earlier disrupted succession with extensional shearing concentrated within thin
(centimeters-to decimeters thick) and penetrative shear
zones.
The recognition of the mechanisms forming these blockin-matrix structures provided us important information
on both original stratigraphy and tectonic evolution of
the Monviso Meta-ophiolite Complex. Documenting
mode and time of the processes forming block-in-matrix units, is thus a relevant approach in studying the
Alpine meta-ophiolites and modeling exhumed convergent plate margins.
REFERENCES
- Angiboust S., Agard P., Raimbourg H., Yamato P. &
Huet B. (2011), Subduction interface processes recorded by eclogite-facies shear zones, Lithos, 127, 222-238.
- Balestro G., Fioraso G. & Lombardo B. (2011), Geological map of the upper Pellice Valley (Italian Western
Alps), Journal of Maps, 2011, 634-654.
- Balestro G., Lombardo B., Vaggelli G., Borghi A., Festa A. & Gattiglio M. (in press), Tectonostratigraphy of
the northern Monviso Meta-ophiolite Complex (Western Alps). Italian Journal of Geosciences.
- Castelli D., Compagnoni R., Lombardo B., Angiboust
S., Balestro G., Ferrando S., Groppo C., and Rolfo F.,
2014. The Monviso meta-ophiolite Complex: HP metamorphism of oceanic crust & interactions with ultramafics. Geological Field Trips, ISSN: 2038-4947.8.35.
6
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
- Festa A., Pini G.A., Dilek Y. & Codegone G. (2010),
Mélanges and mélange forming processes: Historical
overview and new concepts. International Geology Review, 52, 1040–1105.
- Guillot S., Schwartz S., Hattori K., Auzende A. &
Lardeaux J. (2004), The Monviso ophiolitic Massif
(Western Alps), a section through a serpentinite subduction channel. In Beltrando M., Lister G., Ganne J.,
and Boullier A. (eds.), Evolution of the western Alps:
insights from metamorphism, structural geology, tectonics and geochronology. Journal of the Virtual Explorer,
16, 3.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Geological setting of the southern termination of the western Alps arc
(Maritime and Western Ligurian Alps, Nw Italy)
Barale L.(1), Battaglia S.(2), Bertok C.(1), d’Atri A.(1), Ellero A.(2), Leoni L.(3), Martire L.(1), Piana F.(4)
(1) Dipartimento di Scienze della Terra, Università di Torino, Italy
(2) CNR - Istituto di Geoscienze e Georisorse, Pisa, Italy
(3) Dipartimento di Scienze della Terra, Università di Pisa, Italy
(4) CNR - Istituto di Geoscienze e Georisorse, Torino, Italy
The southern termination of the Western Alps arc (Maritime and Western Ligurian Alps) tails off the orogenic
belt along a complex transpressive system (Michard et
al., 2004) comprised between the External Briançonnais
Front, the boundary faults of the Argentera Massif and
the Limone-Viozene Zone (Piana et al., 2009).
This region, in which the transition from internal high
pressure metamorphic rocks to external very low grade
and non-metamorphic rocks occurs, consists of an assemblage of juxtaposed tectonic units elongated on average ESE-WNW direction (Malaroda, 1970; Gidon,
1972) and separated by double-vergent (to SW and NE)
thrusts and strike-slip faults (among which the Stura
Fault Auct. is the more largely known, although strongly debated).
The stratigraphic and structural setting of these units
has been recently revised by mapping their macroscale
boundary faults and evaluating the affinity degree of their
stratigraphic successions with those of the main paleogeographic domains (Briançonnais, Subbriançonnais,
Dauphinois, Provençal domains and the Eocene-Oligocene Alpine foreland basin) (Piana et al., 2009; Piana et
al., 2014). A deep revision of the relations between the
Alpine tectonic units and the Meso-Cenozoic paleogeographic domains has been done.
Great efforts have been also dedicated in discovering the
pre-Alpine physiographic features such as paleo-escarpments and stratigraphic discontinuities that controlled
the facies lateral variations within each unit (Bertok et
al., 2011; 2012). This resulted in a partial re-interpretation of the overall tectonic setting and evolution. Researches also focused on Mesozoic faults and fractures
activity by studying the petrogenetic processes induced
by hosted fluid circulation, consisting in the dolomitization of huge rock masses (Barale et al., 2013; Martire et
al., 2014) and generation of hydrothermal marbles (Rossetti et al., 2014).
Furthermore, the crucial role, for kinematic reconstruc-
tions, of the Early Oligocene chaotic complexes of the
Alpine foreland basin succession was investigated (Perotti et al., 2012).
Finally, reconstruction of the metamorphic evolution
has been performed by analyses of the illite and chlorite Crystallinity Index (Piana et al., 2014) in some
tectonic units placed above and below the External
Briançonnais Front (recording both anchimetamorphic conditions), the tectonic slices of Helminthoides
Flysch involved in the main ESE-WSW transpressive
shear zones (also affected by anchimetamorphic conditions) and the S.Remo-M.Saccarello Ligurian Unit
placed at the geometric top of the Western Ligurian
Alps, that conversely show only diagenetic conditions.
In conclusion, our researches indicate that the southern termination of the Western Alps was characterized by:
- marked tectonic activity since Mesozoic times (important hydrothermal activity and tectonic control on
sedimentary evolution in the Cretaceous-Paleogene
time span);
- deposition of Helminthoides Flysch-type successions on the Provençal European paleomargin and
involvement of Helminthoides Flysch slices in the
regional transpressive shear zones since the very beginning of the Alpine tectonic stage;
- persistence of convergent-wrench tectonics since
Early Cretaceous up to at least Oligocene times;
- absence of metamorphic gap across the External
Ligurian Briançonnais Front and moderate dip-slip
displacement across it, if compared with the width of
the associated shear zone system.
These data and interpretation should be considered
for the reconstruction of the Alpine-Apennine system
evolution, where major E-W transfer zones have been
often invoked as crucial kinematic features connecting, since the Late Eocene, the Ligurian Alps and
Northern Apennines structural domains.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
REFERENCES
- Barale, L., Bertok, C., d’Atri, A., Domini, G., Martire,
L. & Piana, F. (2013), Hydrothermal dolomitization of
the carbonate Jurassic succession in Provençal and Subbriançonnais Domains. Comptes-Rendus Geoscience,
345, 47–53.
- Bertok, C., Martire, L., Perotti, E., d’Atri, A. & Piana,
F. (2011), Middle–Late Jurassic syndepositional tectonics recorded in Ligurian Briançonnais. Swiss J. Geosci.,
104, 237–255.
- Bertok, C., Martire, L., Perotti, E., d’Atri, A. & Piana, F. (2012), Kilometre-scale palaeoescarpments as
evidence for Cretaceous synsedimentary tectonics in the
External Briançonnais. Sedim. Geol., 251, 58–75.
- Gidon, M. (1972), Les chaînons briançonnais et subbriançonnais de la rive gauche de la Stura entre Bersezio
et le Val de l’Arma (Italie). Géol. Alpine, 48, 87–120.
- Malaroda, R. (Ed) (1970), Carta Geologica del Massiccio dell’Argentera, 1:50.000. Mem. Soc. Geol. Ital., 9.
- Martire L., Bertok C., d’Atri A., Perotti E. & Piana
F. (2014), Selective dolomitization by syntaxial overgrowth around detrital dolomite nuclei: a case from the
Jurassic of the Ligurian Brianconnais. Journ. Sed. Res.
84, 40-50.
- Michard, A., Avigad, D., Goffé, B. & Chopin, C.
(2004), The high-pressure metamorphic front of the
south Western Alps. Schweiz. Min. Petr. Mitt., 84,
215–235.
- Perotti, E., Bertok, C., d’Atri, A., Martire, L., Piana,
F. & Catanzariti, R. (2012), A tectonically-induced
Eocene sedimentary mélange in the West Ligurian
Alps, Italy. Tectonophysics, 568–569, 200–214.
- Piana, F., Musso, A., Bertok ,C., d’Atri, A., Martire,
L., Perotti, E., Varrone, D. & Martinotti, G. (2009).
New data on post-Eocene tectonic evolution of the
External Ligurian Briançonnais. It. J. Geosci., 128,
353–366.
- Piana, F., Battaglia, S., Bertok, C., d’Atri, A., Ellero, A., Leoni, L., Martire, L. & Perotti, E. (2014),
Illite and chlorite cristallinity as a constraint for the
kinematic evolution of the External Briançonnais
front in the Western Ligurian Alps. Accept. paper, It.
J. Geosci.
- Rossetti, P., Barale, L., Bertok, C., d’Atri, A., Martire, L. & Piana, F. (2014), The Valdieri marbles:
the result of a localised recrystallization and metasomatism related to a focused flow of REE-rich fluids.
Congr. SGI-SIMP, Milano, Sept. 10–12, 2014.
9
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Geological and geophysical evidences for diapirism in south-eastern Sicily
(Italy) and implications on paleo-tectonics of the western Ionian domain
Giovanni Barreca, Carmelo Monaco
Department of Biological, Geological and Environmental Science, University of Catania, Italy
A recent investigation on the northern margin of the
Hyblean Plateau in south-eastern Sicily (S. Demetrio
horst) highlights the occurrence of a clayey diapiric intrusion, previously unidentified into the foreland
carbonate series. A ~270 long and ~30 m high quarry wall-section provided the opportunity to study
excellent exposure of the rocks and their reciprocal
geometrical relations. Results from field analysis revealed that rocks consist of volcanic products and sedimentary beds resting on greenish chaotic clays, that
are unusual deposits for the Hyblean Plateau. Green
clays are internally affected by contractional deformation whereas the adjacent rocks are deformed only by
a set of low-angle and domino-arranged normal faults.
The occurrence of two distinct deformation patterns
(contraction and extension), confined within the same
structural level, suggests that their nucleation could be
intimately related. Geometry of normal faults (LANF)
indicates that they nucleated in a gravity gliding deformation context triggered by the strong uplift due to
the diapiric emplacement. Available seismic reflection
sections confirms that mud diapirism occurs also in the
adjacent marine setting, about 18 km southeast from
that observed on-land.
Previous petrological studies (Manuella et al., 2012)
elucidated the composition of the green clays that consist of hydrocarbons-rich serpenitinite-bearing muds
interpreted as the product of flocculation from a mixture of hot Si-rich fluids and cold seawater in a Early
to Middle Triassic (~246 My, see Sapienza et al., 2007)
serpentinite-hosted hydrothermal system (Scribano,
2006).
Taking into account that clays formed as a result of
alteration of serpentinite rocks and that serpentinization commonly takes place in oceanic ridges (Karson
et al., 1987; Cannat et al., 1995) or along highly fractured transform zone (Cann et al., 2001; Ildefonse et
al., 2007) an ancient oceanic transform (Permian-Triassic according to Catalano et al., 2001; Early to Middle Permian according to Vai, 2003), probably linking
distinct segments of the Ionian oceanic ridge (Catalano
et al., 2001),can be imaged as a source environment for
serpentinites and their associated products of alteration
(e.g. the green clays).
The mud diapirs originated from the uprising of pre-existing serpentinite bodies and others products of alteration probably developed along the inferred ancient
ridge-transform intersection (here named the “Hyblean
Transform”) where a hydrothermally altered mantle
wedge occurred. This interpretation is supported by
seismic, magnetic and gravimetric anomalies beneath
the analyzed area and has implications on its geodynamic evolution.
REFERENCES
- Cann, J.R., Prichard, H.M., Malpas, J., Xenophontos,
C., 2001. Oceanic inside corner detachments of the Limassol Forest area, Troodos ophiolite, Cyprus. J. Geol.
Soc. Lond. 158, 757–767.
- Cannat, M., Mevel, C., Maia, M., Deplus, C., Durand,
C., Gente, P., Agrinier, P., Belarouchi, A., Dubuisson,
G., Humler, E., Reynolds, J., 1995. Thin crust, ultramafic exposures, and rugged faulting patterns at the
Mid-Atlantic Ridge (22–24°N). Geology 23, 49–52.
- Catalano, R., Doglioni, C., Merlini, S., 2001. On the
Mesozoic Ionian Basin. Geophys.J. Int. 144 (2001),
49–64.
- Ildefonse, B., Blackman, D.K., John, B.E., Ohara, Y.,
Miller, D.J., MacLeod, C.J., 2007. Oceanic core complexes and crustal accretion at slow-spreading ridges.
Geology 35, 623–626.
- Karson, J. A., Thompson, G., Humphris, S. E., et al.
1987. Along axis variations in seafloor spreading in the
MARK area. Nature, 328:681-685.
- Manuella, F.C., Carbone, S., Barreca, G., 2012. Origin of saponite-rich clays in a fossil serpentinite-hosted hydrothermal system in the crustal basement of the
Hyblean Plateau (Sicily, Italy). Clays and Clay Minerals 60, 18–31.
- Sapienza, G., Griffin, W.L., O’Reilly, S.Y., Morten,
L. 2007. Crustal zircons and mantle sulfides: Archean
to Triassic events in the lithosphere beneath south-eastern Sicily. Lithos, 96, 503–523.
10
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
- Scribano, V., Sapienza, G.T., Braga, R., and Morten,
L. 2006. Gabbroic xenoliths in tuff-breccia pipes from
the Hyblean Plateau: insights into the nature and composition of the lower crust underneath South-eastern
Sicily, Italy. Mineralogy and Petrology, 86, 63–88.
- Vai, G.B., 2003. Development of the palaeogeography of Pangaea from Late Carboniferous to Early
Permian. Palaeogeography, Palaeoclimatology, Palaeoecology196, 125–155.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
The concept of ophiolites from Alexandre Brogniart to Piero Elter
Daniel Bernoulli
Department of Earth Sciences, Swiss Federal Institute of Technology (ETH), Zürich, and Institute of
Geology, University of Basel, Switzerland
The term ophiolite, introduced by Brogniart in 1813,
was originally synonymous with serpentinite; however,
as early as 1821, Brogniart recognized the close association of serpentinites, gabbros, “variolite” and jasper
(chert) in the Apennines of Liguria and Tuscany and
included them into his “ophiolitic or serpentine formation”. In the 19th century, this association was recognized in many, particularly Alpine-type mountain belts
and later became known as the Steinmann Trinity. The
rocks of the Steinmann Trinity were thought to be a consanguineous association of intrusive (e.g., Steinmann)
or extrusive (e.g., Lotti) igneous rocks or a combination
of both, related in one way or another to the evolution of
the mountain belts.
Because of the perceived antiquity and permanence of
oceans and continents, mountain chains were generally thought to originate from narrow, elongated, unstable belts, the geosynclines, circling the continents
or following “zones of crustal weakness” from which
geanticlines and finally mountain belts inevitably would
develop. However, the anactualistic concept of the geosyncline had already met with major critiques, and as
early as 1905, Steinmann considered the association of
peridotite, “diabase” (basalt/dolerite) and radiolarites in
the Alps and Apennines as characteristic of the deepocean floor; eventually Argand and E.B. Bailey placed
Steinmann’s interpretation of the ophiolites into the context of continental drift and ocean evolution.
Between 1930 and 1960, new problems were arising.
The results of experimental petrology showed that peridotic magmas “were not possible” under reasonable
conditions in the crust, and that, on the other hand,
serpentine minerals were unstable above 550°C. Large
stratiform mafic-ultramafic complexes could form at
best by fractional crystallization of a basaltic magma
and gravitational segregation. However, this interpretation was not applicable to the large ophiolite complexes
of the eastern Mediterranean area because of their high
ultramafic/mafic ratios. The problem could only be
solved when it was recognized that Alpine-type peridotites were displaced fragments of the Earth mantle
tectonically incorporated into mountain belts, representing either exhumed sub-continental mantle or oceanic mantle lithosphere associated with igneous rocks
derived from partial melting of the mantle.
In contrast to the east-Mediterranean area, where the
standard model of ophiolite “stratigraphy”, canonized
1972 by the Penrose Field Conference on Ophiolites,
was developed in line with the model of the oceanic
lithosphere, the succession in west-Mediterranean did
not meet this model. These ophiolite associations are
characterized by relatively small amounts of partial
melting, the gabbros forming smaller intrusive bodies
within the mantle rather than a continuous oceanic layer 3; the absence of a sheeted-dyke complex; and the
frequent occurrence of oceanic sediments resting with
an unconformable depositional contact on mantle-derived serpentinized peridotites or exhumed plutonic
rocks. Such a scenario is best explained by extension
of both the continental and the oceanic lithosphere,
exhumation and serpentinization of the mantle rocks
at the sea floor, intrusion and exhumation to the sea
floor of gabbroic rocks and submarine volcanicity. Indeed, such a scenario, now found along ocean–continent-transitions of passive margins and Atlantic-type
slow-spreading ridges, where extension is accommodated by tectonic processes rather than by magmatic
activity, was for the first time described in an orogen
in a coherent way by Piero Elter and his co-workers,
anticipating much of the current concepts. During the
last forty years, Elter’s views have been modified and
refined by comparisons of Alpine ophiolites with extant Atlantic-type passive margins and slow-spreading
ridges, but they will remain a brilliant example of a
combination of meticulous field observation and inspired interpretation.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Reconciling the Geology of the Emilia Apennines and Tuscany across
the Livorno-Sillaro Lineament, northern Apennines, Italy
Giuseppe Bettelli (1), Filippo Panini(1), Francesca Remitti(1), Paola Vannucchi(2)
(1) Department of Chemical and Geological Sciences, University of Modena and Reggio Emilia, , Italy
(2) Department of Earth Sciences, University of Florence and Department of Earth Sciences, Royal Holloway
University of London, UK
Surface expression of lithospheric faults may vary
greatly as they can develop a wide range of geomorphic/topographic features and various kinds of superficial geological/structural mismatchings. The “Livorno-Sillaro Lineament” (Nirta et alii, 2007; Pascucci et
alii, 2007; Bettelli et alii, 2012) is one of the most important transverse lineaments of the Northern Apennine
orogen. The lithospheric-scale role of this structure has
been recognized long time ago by various authors on the
base of different geophysical, geological and geomorphic data, although its origin is still not well defined.
Also the exact surface characters of this structure are
still not well-defined, we think because they are mainly
based on old and out-of-date geological data.
We present a review of the more recent stratigraphical
and structural data related to the geology across the
“Sillaro Lineament”, SL, the northeasternmost segment of the “Livorno-Sillaro Lineament”. Based on a
re-examination and reinterpretation of the existing information about the regional geology of the Northern
Apennines we conclude that the supposed mismatching
of the Ligurian/Subligurian Units on the two sides of
this lineament is mainly due to a lack of knowledge
and to an inadequate correlation between corresponding units. Nevertheless, we recognize that this structure
(along with the Secchia transverse lineament) greatly
influenced the growth and the evolution of the oceanic
accretionary prism/Ligurian/Subligurian thrust-nappe
from the late Eocene to the late Serravallian, and also
later on. In particular, we point out that at least the easternmost segment of this structure not only played an
important role on the differential growth of the Ligurian/Subligurian accretionary prism-thrust nappe, but that
it was responsible for the different amount of translation
of the Ligurian Units on both side of the lineament.
Our conclusions and interpretations include:
1) the Sillano/Mt Morello succession, typically cropping out SE of the SL in eastern Tuscany, represents
the source rocks of the Ligurian blocks forming the
Sestola-Vidiciatico tectonic unit and similar units (e.g.,
Coscogno-Montepastore tectonic unit: Remitti et alii,
2013) cropping out NW of the SL and along the SL itself;
2) the External Ligurian unit variously named as
Samoggia/Val Sillaro/Val Marecchia Varicoloured
Shales, AVS, and the overlying lower to middle Eocene
turbidites (e.g., Savigno Fm) cropping out in the Emilia
Apennines - i.e., NW of the SL – represents a lateral
and more internal equivalent of the Sillano/Mt Morello
succession. The AVS were extensively present also SE
of the SL, as testified by the large klippen in the Romagna Apennines (Savio and Marecchia valleys) and many
small klippens in the Umbria area (Umbertide-Gubbio
area);
3) along and SE of the SL the AVS form the stratigraphic base of the Mt Morello Fm. Therefore, also this unit
is present on both sides of the SL;
4) the pre-middle Eocene Subligurian Units cropping
out NW of the SL (Argille e Calcari di Canetolo Fm and
Calcari del Groppo del Vescovo Fm) do not correspond
to the so called Subligurian Units cropping out SE of the
SL (i.e., in Tuscany). The latter are the result of the sedimentation in a particular paleogeographic domain, transitional to the Tuscan domain, absent or not preserved
NW of the SL. This seems to represent the only real
difference in the geology of the Ligurian/Subligurian
thrust nappes NW and SE of the SL.
All the available data show that until the late Serravallian the thrust front of the Ligurian nappe was located in
the same position across the SL. However, starting from
the early-late Tortonian a differential translation of the
Ligurian nappe NW of the SL took place, progressively
reaching the present day position. With the exception of
the Marecchia area, in the Romagna and Umbria Apennines (SE of the SL), instead, the thrust front of the Ligurian nappe remained more or less in the same position
it reached in the late Serravallian. This implies that in
the Northern Apennines the transverse SL played also
an important role in the different amount of translation
of the Ligurian thrust-nappe.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
REFERENCES
- Bettelli, G., Panini, F., Fioroni, C., Nirta, G., Remitti,
F., Vannucchi, P. & Carlini, M. (2012), Revisiting the
Geology of the “Sillaro Line”, Northern Aprnnines, Italy. Rendiconti Online Società Geologica Italiana, 22,
14-17.
- Nirta, G., Principi, G. & Vannucchi, P. (2007), The Ligurian Units of Western Tuscany (Northern Apennines):
insight on the influence of pre-existing weakness zones
during ocean closure. Geodinamica Acta, 20/1-2, 71-97,
doi:10.3166/ga.20.71-97
- Pascucci, V., Martini, I.P., Sagri, M. & Sandrelli, F.
(2007), Effects of transversal structural lineaments
on the Neogene-Quaternary basins of Tuscany (inner
Northern Apennines, Italy). In: G. Nichols, E. Williams
& C. Paola (Eds.), Sedimentary Processes, Environments and Basins: a Tribute to Peter Friend (pp.155182). Special Pubblication no. 38 of the International
Association of Sedimentologists.
- Remitti, F., Balestrieri, M.L., Vannucchi, P. & Bettelli,
G. (2013), Early exhumation of underthrust units near
the toe of an ancient erosive subduction zone: A case
study from the Northern Apennines of Italy. Geological
Society of America Bullettin, 125, 1820-1832, ISSN:
0016-7606.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Piero Elter: from the Apennines to the Atlantic
Enrico Bonatti
Lamont Doherty Earth Observatory, Columbia University, USA
Istituto Scienze Marine, CNR Bologna, Italy
During the mid- and late-sixties of the last century, Piero Elter was often taking off from Pisa to
roam around the mountains and hills of the western
Apennines, doing field work also in the Ligurian ophiolites. We were then in the very early
stages of the Plate Tectonic revolution: the nature
and origin of ophiolites was a matter of debate
and speculation. Elter and coworkers (in particular F. A. Decandia) in a couple of slim papers
put forward some original ideas on the nature of
the Ligurian ophiolites, suggesting that ophiolitic
serpentinite-gabbro-basalt associations originated in
young mid ocean ridge systems during the early
stages of opening of an ocean. The initial stages
in the exploration of the mid Atlantic Ridge, taking
place at about that time, and subsequent studies of
the Red Sea rift, gave strong support to Decandia
and Elter’s intuitions.
On a more personal note, I would like to recount
how a “tesina” I did in Pisa under the supervision
of Piero Elter contributed soon after to my focusing my research on the geology of the oceans.
15
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
The geological sheet n° 261 – Lucca ( CARG):
main results and some suggestion
Andrea Cerrina Feroni (1) and Alberto Puccinelli (2)
(1) Centro di Geotecnologie, Università di Siena, Italy
(2) Dipartimento di Scienze della Terra, Università di Pisa, Italy
The “official” geological cartography of the national territory has been improved by the scientific community
(University and CNR).
The CARG Project (1:50,000), now in stand by for lack
of economic resources, represents a significant opportunity in the development of regional geology. This branch
of the Earth Sciences, whose laboratory is the mountain,
needs for its increase in new and methodologically updated geological mapping.
The Geological Sheet N°261-Lucca, of CARG Project,
is in progress by CGT UNISI.
The Sheet N° 261 – Lucca (approximately 590 kmq) includes an area of low mountains and hills of the Serchio
River Middle Valley. An important role is played by the
Lucca Plain. In fact, it represents a continental sedimentary basin structured between Rusciniano (? lower Villafranchian) and Holocene, together with the clastic and
terrigenous units outcropping in Montecarlo-Cerbaie
hills.
In this poster paper the Authors illustrate the most significant results and expose, in particular, their points of
view on the structure of the Tuscan Nappe in the Pescaglia region.
In this territory, located to the Southeast of the Apuan
Alps tectonics window, the Tuscan Nappe is exposed
with excellent outcrops and represents the main topic of
recent structural studies (Carosi et al. 2005 )
In comparison with the past knowledge, we propose a
new geometric and kinematic resolution of the major
folds overturned, N120 -N160 strike, and facing to SW.
The schematic geological section of fig 1 shows the
polyphasic character of the Tuscan Nappe structure near
Pescaglia.
Axial planes of subisoclinal folds D1 (Campore T. Anticline, Mt Piglione Syncline and Pescaglia Anticline) are
deformed till to overturning in the Mt. Prana synforme
(D2). The original facing to NE of D1 folds appears so
inverted in the overturned limb of second phase (D2)
Mt. Prana synforme.
The Mt. Prana synforme is consequently the only major
fold in Pescaglia area with real facing to SW.
In D1 phase there is the development of low-angle shear
zones major structures scale (duplex structures) and
mesoscale (s-c tectonite ). Duplex structures were reconstructed at different levels between the Cavernoso
Limestone and Macigno Sandstone. In particular, the
redoubling of lithofacies coupled Scaglia Fm. between
Maiolica Limestone(Floor thrust) and Macigno Sandstone (Roof thrust) (Freddana valley) are consider as
duplex structures
Shear zones are developed in D1 phase even in the most
rigid units of the sequence as in the “Scaglia calcarea”
case (Coniacian ?) of Freddana valley (surroundings of
Montefegatesi). In these outcrops, the involvement of
D1 fabrics in the D2 phase overturned folds is evident.
In Massarosa Mts.(near Chiatri area), the polyphasic
stacking is well documented by the doubling of the Maiolica-Scaglia coupled (D1), under the Macigno sandstone, involved in the overturn in folds N160 strike
facing to SW (D2)
Fig 2 shows s-c tectonite (top to NE) borne in Marne a
Posidonomya Fm (Dogger) into the shear zone of Foce
di Bucine, along the road to the Matanna refuge at the
base of the of Maiolica Limestone (Neocomiano).
In D1 phase, the development of penetrative slaty cleavage (S1) slightly tilted on the layering (So) in less rigid
or ductil behaviour units of Tuscan stratigraphic succession (Marne a Posidonomya, Scaglia) is also widespread.
The Foce di Sella Fault subtend the overturned limb of
the Mt. Prana synforme (fig. 1). This fault and in general all high-angle faults analysed shows evidences of
Figure 1
16
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Figure 2
polyphasic kinematic. It is often an association of transpressional to compressional kinematic with extensional
kinematic.
The analytical data collected suggest that high-angle
faults are generated in transpressive stress field and that
only in the final stage their activities acted as normal
faults.
In this conceptual model, the folds of late stage D2 with
the high angle faults NW-SE strike appear compatible.
The overturned Mt. Prana synforme takes the meaning
of a synclinal footwall in relation to the Foce di Sella
Fault in its early transpressive step.
A low-angle Extensional Tectonics, clearly post phase
D2 ,probably related to structuration of Tyrrenian Basin,
is very well expressed at the major scale and mesoscale
in the Oltre Serchio and Massarosa Hills.
REFERENCES
- Carmignani L., Giglia G. & Kligfield R. (1978). Structural evolution of the Apuane Alps: an example of continental margin deformation in the Northern Apennines,
Italy. Jour. Geol., 86: 487-504.
- Carmignani L. & Kligfield R. (1990). Crustal extension in the Northern Appennines: thetransition from the
compression to extension in the Alpi Apuane core complex.Tectonics, 9: 1275-130.
- Carosi R., Montomoli C. & Pertusati P. C.
(2004). Late tectonic evolution of the Northern
Apennines, the role of contractional tectonics in
the exhumation of the Tuscan unit. Geod. Acta,
17: 253-273.
- Carosi R., Frassi C., Montomoli C. & Pertusati P.
C. (2005). Structural evolution of the
Tuscan Nappe in the southern sector of the Apuan
Alps metamorphic dome (Northern Apennines, Italy). Geol. Jour., 40: 103-119.
- Cerrina Feroni A. & Patacca E. (1975). Considerazioni preliminari sulla paleogeografia del Dominio Toscano Interno tra il Trias superiore e il
Miocene medio. Atti soc. Tosc. Sci. Nat., Serie A,
82: 43-54.
- Cerrina Feroni A., Plesi G., Fanelli G., Leoni L.
& Martinelli P. (1983). Contributo alla conoscenza dei processi metamorfici di grado molto basso
(anchimetamorfismo) a carico della Falda Toscana
nell’area di ricoprimento apuano. Boll. Soc. Geol.
It., 102: 269-280.
- Fazzuoli M. (1981). Considerazioni preliminari
sul Calcare selcifero della Val di Lima (Giurassico
superiore) Toscana nord-occidentale. Mem. Soc.
Geol. It., 21: 193-201, 3 figg., Roma.
- Giannini E. & Nardi R. (1965). Geologia della
zona nord - occidentale del Monte Pisano e dei
Monti d’Oltre Serchio (prov. Di Pisa e Lucca).
Boll., Soc. Geol. Ital., 84: 198-270.
- Pertusati P. C., Plesi G. & Cerrina Feroni A.
(1979). Alcuni esempi di tettonica polifasata nella
Falda Toscana. Boll. Soc. Geol. It., 96: 587-603.
- Trevisan L., Brandi G. P., Dallan L., Nardi R.,
Raggi G., Rau A., Squarci P., Taffi L. & Tongiorgi M. (1971). Note illustrative alla carta geologica d’Italia alla scala 1:100.000. Foglio 105
Lucca. Ministero dell’Industria, del Commercio e dell’Artigianato, Direzione Generale delle
Miniere, Servizio Geologico d’ Italia, 1-51.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
The Portofino Conglomerate (Eastern Liguria):
stratigraphic notes
Barbara Corsi(1), Franco Marco Elter(2), Michele Piazza(2)
(1) Corso Garibaldi 52/10 - Chiavari (Genova), Italy
(2) DISTAV - Departement of Earth Science, Environment and Life, University of Genova, Italy
The Portofino Conglomerate (CdP) crops out in the
Eastern Liguria (Riviera di Levante), unconformably
overlies the tectonostratigraphic Antola Unit and is
composed of an about 460 m thick succession of poorly
beded conglomerates with interbedded few sandy and/
or silty beds and lenses. On the whole, the conglomerates are moderately to poorly sorted, clasts-supported,
with sandy to sandy-silty matrix and carbonate cement.
Compositional evidences allow to distinguish three different lithofacies (Corsi, 2003), from bottom to top with
gradational passages: Paraggi, Monte Pallone and Monte Bocche Lithofacies. The Paraggi Lithofacies (about
250 m in thickness) is characterized by the dominance
of carbonate (marls, marly-limestones, calcarenites,
biocalcirudites) clasts (60-88%), the low occurence of
volcanic (pillow lavas/ porphiric diabases, 1-2%) and
metamorphic (calcschists and marbles, 1-2.5%) clasts
and by carbonate matrix. The Monte Pallone Lithofacies (about 60 m in thickness) is characterized by the
decrease of carbonate (marls, marly-limestones, limestones with cherts) clasts (2-29%) and the increase of
quartz clasts (5-32%), HP-metabasites, (4-30%), metamorphic (marbles, calcschists, micaschists 4-70%),
and by quartz-rich sandy matrix and carbonate cement
balanced proportion. The Monte Bocche Lithofacies
(about 150 m in thickness) is characterized by the
strong decrease of the carbonate clasts (0-15%) and the
dominance of marbles/dolostones (4-50%), HT-metamorphic (gneiss, migmatites, orthogneiss, 4-20%) and
noncarbonate sedimentary (anagenites, green/whitish
quartzites, (10-37%) clasts, and the subordinate (less
than 10 %) presence of intrusive igneus (granitoids and
gabbros) clasts, and by the occurrence of quartz-domi-
nated matrix and minor carbonate cement.
In terms of provenance, the carbonate clasts appear to be
supplied by the Antola Unit flysch or by a similar sedimentary complex; the metabasite, marble, calcschist,
and volcanic clasts may be related to the oceanic Piedmontese Units, while the acid metamorphic, granitoid,
HT-metamorphic, and quartz-rich sedimentary ones
might be supplied by the Briançonnais Units.
According to the geologic and sedimentologic evidence,
the CdP can be regarded the result of a delta deposition
in coastal to shallow marine environment; paleocurrents
seem to suggest a feeding area located at the west of the
present-day CdP position (Corsi, 2003).
The CdP age is generally reported as “Oligocene”,
but its fossil content is very poor. Until now, only one
specimen of the plaktonic foraminifer Globigerinatheka (middle - upper Eocene) in the matrix of the Paraggi
Lithofacies conglomerates, and coal lenses, coalified remains and rare bioclasts, unevenly distributed throughout the succession, were found. The few biocalcirudite
clasts occurring in the Paraggi Lithofacies exhibit a fossil content (discocyclinids and red calcareous algae) that
indicates an Eocene age.
Finally, the relationship with the, probably, coeval conglomeratic units cropping out in the surrounding areas
(i.e.: San Paolo Fm., Molare Fm., Pianfolco Fm., Savignone Conglomerate) remains unclear.
REFERENCES
- Corsi B. (2003). Eventi tettonico-sedimentari del settore tra Chiavari e Genova Nervi nel quadro dell’evoluzione geodinamica del sistema Ligure Balearico e Tirrenico. PhD Thesis - Università di Genova, 257 pp.
18
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Struttura ed evoluzione della catena alpina:
dallo Structural Model of Italy al Progetto Crop ed ai loro sviluppi
Giorgio V. Dal Piaz
Accademia delle Scienze di Torino, Italy
La geologia alpina, fortemente influenzata dai modelli
di Emile Argand e Rudolf Staub, subisce alla fine degli
anni 60’ l’impatto della plate tectonics, senza partecipare alla sua formulazione. I primi tentativi di applicare i
canoni della nuova tettonica globale all’evoluzione convergente delle Alpi sono rappresentati da alcuni modelli a piccola scala di H.P. Laubscher (1969, 1970) che,
incerto nello stabilire il ruolo delle placche in gioco,
concepisce la contemporanea subduzione di entrambe
verso una comune zona radicale, con struttura analoga
al “tectogene” di Hess (1939). La subduzione litosferica ed il suo modello termico forniscono adeguata spiegazione alla genesi del metamorfismo eclogitico (Dal
Piaz 1971; Ernst 1971; Fry & Fyfe 1971), ben noto dai
tempi di Franchi, Zambonini ed altri grandi dell’epoca. Nelle Alpi occidentali, il metamorfismo eclogitico
nel sistema tettonico Sesia-Dent Blanche (Dal Piaz &
Nervo 1971; Dal Piaz al. 1972; Compagnoni & Maffeo
1973) e quello nelle unità europee distali del Monte
Rosa-Gran Paradiso (Compagnoni & Lombardo 1974;
Dal Piaz 1974; Frey et al. 1974) sono la prova che non
solo la litosfera oceanica, ma anche coerenti sezioni di
crosta continentale leggera erano discese nella zona di
subduzione sino a profondità sottocrostali, vincendo
la propensione al galleggiamento postulata dai fisici.
La scoperta di coesite nel Dora-Maira (Chopin 1984)
aumenta la profondità massima raggiunta da unità del
margine continentale passivo europeo sino a valori prossimi ai 100 km, complicando ulteriormente il problema
dell’esumazione. Il Progetto Finalizzato Geodinamica è
un momento di rinascita e di grande fervore delle Geoscienze italiane, promuove una fattiva cooperazione tra
geologia e geofisica, sdogana definitivamente in Italia i
canoni della tettonica delle placche e fornisce le prime
solide basi per la valutazione dei rischi naturali e la
loro mitigazione. Il sottoprogetto “Modello Strutturale
d’Italia”, coordinato da Paolo Scandone, realizza negli
anni 80’ la “Synthetic structural-kinematic map of Italy”
(1989) e lo “Structural Model of Italy”, in cinque fogli alla scala 1:500.000: il modello copre l’intera catena
delle Alpi, dalla pianura padana all’avanpaese europeo
Figura 1 – Carta tettonica delle Alpi, evoluzione schematica dello Structural Model. Austroalpino occidentale (WA)
ed orientale (EA), Alpi Meridionali (SA); Unità oceaniche
ed europee: Zona Pennidica (P) e ofioliti (blu), con i Klippe
delle Prealpi Romamde e del Chiablese (Pk) e le finestre tettoniche dell’Ossola-Ticino (oyw), Engadina (ew), Tauri (tw)
e Rechnitz (rw); Elvetico (H). Lineamento Periadriatico (pl),
Avanfossa della Molassa (M), Avampaese europeo (EF),
Avampaese padano-adriatico (PA), Bacino Pannonico (PB),
Dinaridi (DI), Appennini (AP) (Dal Piaz, Bistacchi & Massironi, Episodes 2003).
e da Vienna alla Provenza (Fig. 1). La legenda, impostata su base strutturale, distingue la catena collisionale a
vergenza europea dalle Alpi Meridionali a vergenza
padano-adriatica, indica le varie unità in successione da
tetto a letto e le completa con distinzioni di carattere litostratigrafico e metamorfico. Ad esempio, rappresenta
le unità policicliche di basamento e quelle di copertura,
aderenti o scollate, le unità continentali ed oceaniche
con metamorfismo alpino di subduzione, le unità ofiolitiche riferibili al bacino ligure-piemontese, estese dalle
Alpi occidentali alle finestre dei Tauri e di Rechnitz, e
quelle attribuibili ai bacini vallesano e nord-pennidico,
confermando precedenti correlazioni tra le unità continentali interne e medie della Zona pennidica con quelle
della finestra dei Tauri. Rappresenta plutoni, apofisi e la
precisa ubicazione (asterisco) di centinaia di filoni del
magmatismo calc-alcalino ed ultrapotassico di età oligocenica (32-30 Ma) nel settore interno del prisma collisionale e, almeno in parte, di età pre-Adamello nelle
unità sudalpine a vergenza padano-adriatica.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Figura 2 – Crocodile vs Ductile extrusion model (Transalp
Working Group 2002). Come osservato da Castellarin et al.
(2006), è preferibile il secondo modello; il primo attribuisce
al cuneo pennidico, caldo (metamorfismo in facies anfibolitica) e soffice, l’improbabile ruolo di indenter in grado di penetrare profondamente nella crosta continentale sudalpina,
più fredda e rigida.
E’ stato un lavoro immane, senza supporto digitale, con
carte disegnate a mano ed allestimento per la stampa alla
vecchia maniera, ed alla fine è mancata la forza di scrivere le note illustrative: un’occasione perduta. Il secondo
progetto di grande respiro per la ricerca italiana è stato il
CROP, una serie di esperimenti di sismica a riflessione
crostale, finanziati dal CNR con vari partners e realiz-
zati tra il 1986 e il 1991 (CROP Atlas, 2003). Il progetto è iniziato con il profilo CROP-ECORS, tracciato
attraverso le Alpi nord-occidentali, coordinato da R.
Nicolich e R. Polino e realizzato in collaborazione con
i francesi (Nicolas et al. 1990; Polino et al. 1990). L’esperimento ha fornito la prima chiara immagine dell’esistenza di due Moho indipendenti e ben separate, quella europea, in subduzione sotto il prisma collisionale,
e quella della placca superiore adriatica, al posto della
singola e continua Moho dei modelli classici, depressa
a guisa di sinforme sotto la catena collisionale ispessita:
oggi può sembrare banale, ma è stato un risultato rivoluzionario. Analoghe rotture litosferiche sono state messe
in luce dal profilo CROP Alpi Centrali (Montrasio et al.,
2003) e dal Progetto Transalp (Castellarin et al. 2006;
Luschen et al. 2006; Lammerer et al. 2008), un profilo
sismico crostale esteso da Treviso a Monaco, attraverso
il settore occidentale della finestra dei Tauri. I rapporti
tra il prisma collisionale e la fronte della crosta sudalpina sono stati interpretati in modo diverso (Crocodile
vs Ductile extrusion model; Fig. 2) sulla base di differenti modelli reologici, mentre vi è stato accordo nell’attribuire le discontinuità profonde dell’immagine sismica alla subduzione della placca europea sotto il prisma
collisionale e l’indenter sudalpino. La complessa struttura interna del prisma collisionale è confermata dallo
studio geologico-strutturale del settore occidentale della
finestra dei Tauri, effettuato per il progetto della nuova galleria di base del Brennero (Bistacchi et al. 2007,
2010; Dal Piaz et al. submitted).
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
The tectono-stratigraphic evolution of distal magma-poor rifted margins:
examples from the Alpine Tethys, the E-Indian and
Newfoundland-Iberia rifted margins
Alessandro Decarlis, Gianreto Manatschal, Isabelle Haupert, Emmanuel Masini
IPGS/EOST, Université de Strasbourg, France
The tectonostratigraphic evolution of distal, magma-poor rifted margins still remains a poorly-known
topic despite of the increasing interest driven by new
research opportunities in hydrocarbon exploration. Seismic imaging of modern distal margins suffer the technical tethers of geophysical exploration and moreover
the general lacking of drill holes limits the observations
only to the structure of sedimentary successions. On the
contrary, fossil distal margins preserved inside mountain belts allow the direct observation of rock features,
but exhibit major overprint due to the orogenic deformation and metamorphism that usually concentrates in distal domains. To avoid the incompleteness of the above
cited examples, in this study we couple the observations
on the different passive distal margin datasets. We use
two well-imaged seismic profiles, Iberia-Newfoundland
SCREECH1-ISE1, East India ION GXT-1000 and an
onshore database represented by selected stratigraphic
sections from the Jurassic Alpine Tethys. For the latter,
we focus on the sedimentary successions of different
domains of the former distal rifted margins: the ones
from the Ligurian Prepiedmont and Piedmont domains,
outcropping in the Western Alps (European margin) and
those belonging to the Lower Austroalpine exposed in
the Central Alps in SE Switzerland (Err, Bernina units;
Adria margin). We choose these domains because of
their stratigraphic completeness and the correlatability of the sedimentary successions. We stress that, with
a certain degree of approximation, these areas can be
considered as part of a former “conjugate” rift system
during Jurassic. The aim of this study is to examine the
different datasets into an iterative process where seismic sections act as a framework to determine first-order
tectonic features for non-volcanic rifted margins and
field observations that integrate the seismic datasets as
virtual boreholes, into an attempt to point out the overall tectonostratigraphic evolution. As a result, once the
upper and lower plate geometry sensu rifting has been
defined in the three examples (i.e. respectively the footwall and the hangingwall of the main exhumation fault),
the primary features of sedimentation and their relations
with tectonics have been compared. This lead (1) to a
better comprehension of the sedimentary environment
evolution in the distal margin during the Alpine rifting.
More in general, it allows to (2) decipher the interactions between tectonics, sediment supply and accumulation in distal passive margins, unravelling the different
basin-style and the sediment distribution/composition.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Ophiolitic units of the Northern Apennines as a tool to unravel Schistes
Lustres stratigraphy of the Western Alps and their geodynamic context:
the Urtier Valley example, Cogne, Aosta Valley
Alessandro Ellero(1), Andrea Loprieno(2)
(1) CNR-IGG, Pisa, Italy
(2) Viale Cavagnet 45, Cogne, Aosta, Italy
One of the most significant scientific contribution that
Piero Elter has left us, is undoubtedly represented by the
definition of the stratigraphic features and geodynamic
significance of the ophiolitic units of the Northern Apennines (NA) (Elter & Raggi, 1965a, b; Decandia & Elter,
1972; Elter, 1975a, b; Elter & Marroni, 1991) and their
relationships with the Western Alps (WA) (Elter et al.,
1966; Elter & Pertusati, 1973; Elter, 1993).
Two topics emerge from the extensive work of Elter: i)
the stratigraphic and geodynamic distinction between an
Internal Ligurian Domain, representative of the Ligure-Piemontese oceanic basin, and an External Ligurian
Domain, derived from the Adria distal continental margin, and ii) different significance of depositional setting
for the ophiolitic detritus occurring, at different stratigraphic levels, within the Ligurian units of the NA.
After his extensive field experience in the Ligurian Units
(LU), which lasted many years, once back in the Schistes
Lustres of the Western Alps, Elter was always surprised
by clear similarities in their stratigraphy and shared his
idea that the Ligurian Units (LU) may represent a valuable tool in the study of the ophiolitic units in the Western Alps. In this paper we summarize the main results of
such stratigraphic and structural analyses, originally performed exactly twenty years ago.
The investigated area extends in the Urtier Valley which
is located at the northern flank of the Gran Paradiso Massif, E of Cogne. Our attempt has been to study schistes
lustres ophiolitic units, characterising a stratigraphy comparable to that of the LU. In this way it has been possible to unravel the geometry and the geodynamic context
for the ophiolitic units of the Urtier Valley, similar to that
suggested for the LU of the NA.
Five different tectonic units were mapped in the area, from
the geometrically lowermost to the uppermost they are:
1) the Gran Paradiso basement unit; 2) the Péne Blanche
unit (part of the so-called “Fasceaux de Cogne”); 3) the
Broillot unit (BU); 4) the Bardonney mélange unit (BM);
5) the Tour Ponton and Acque Rosse units.
The two recognized ophiolitic units BU and BM, despite a pervasive metamorphism and an intense deformation, preserve a very characteristic stratigraphic succession, allowing an immediate correlation with similar
sequences of the LU.
The BU is characterized by ophiolitic bodies and related sedimentary cover, represented by the corresponding metamorphic terms of chert (metaquarzite), Calpionella limestone (impure marble) and Palombini shale
(calcschist). The Palombini calcschists are overlain by
metapelites and micaschists, alternated with arenaceous
calcschists and detritic prasinites (metabasic sandstones). This succession has been interpreted as a turbiditic deposit comparable with the Val Lavagna Shale
Formation of NA. Similar correlations were suggested
for other alpine detritic successions (e.g. Col Agnel formation of Cottian Alps by Lagabrielle, 1987). The BU
shows all the features typical of the Internal Ligurian
Domain, so can be interpreted as derived from the Ligure-Piemontese oceanic domain.
The BM is constituted by ophiolites (mainly metabasites) only represented by clasts and/or slices from centimeter to pluridecameter in size within an abundant
carbonate/quarzitic and/or metabasic matrix. This unit
has been correlated with the youngest formation of the
Internal Liguride Units, named Bocco Shale or Colli-Tavarone Formation which consists of pebbly mudstones, pebbly sandstones and ophiolites slide-blocks
in a varicoloured shaly matrix. It is interpreted as an
early Paleocene lower slope deposits sedimented on
the top of the Internal Liguride Units as they approach
the accretionary prism (Elter & Marroni, 1991). Overall, integrating the stratigraphic sequences of the two
ophiolitic units of the Urtier Valley, is possible to reconstruct a stratigraphic succession perfectly correlable
with those belonging to the Internal Ligurian Domain
of the NA, interpreted as recording trench-ward motion
of the oceanic lithosphere (Marroni & Pandolfi, 1996).
A similar analogy between LU successions and ophiol-
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
itc sequences in the Western Alps was proposed for the
Lago Nero Unit, in the Chenaillet Massif (Burroni et al.,
2003).
The structural evolution of the Urtier Valley is characterized by three major deformation stages and related
structures (Loprieno et al., 2009, 2014).
D1 structures are represented by relict microfabric associated with eclogite-facies assemblages and small-scale
isoclinal folds. It is also responsible for early stage of
nappe stack formation.
D2 is the dominant deformation stage, refolding the tectonic contacts between the units, showing D2 isoclinal
folds on all scales, associated with S2 greenschist facies
pervasive mylonitic fabric that represents the main foliation at regional scale. D2 folds axes and L2 lineation
show a common orientation with E-W trend.
D3 is instead characterized by open to close folds with
NE or SW gently dipping axial plane that refold the
composite main foliation S1/S2.
At the scale of the study area, the reconstruction of the
general architecture of the stacked units is facilitated by
stratigraphic markers within the ophiolitic units, showing how the nappe pile as a whole is deformed by a D2D3 interference structure, with a large scale D2 synform
refolded by a large scale D3 Urtier antiform.
Despite intense metamorphic overprint and deformation
history, this contribution testify how a combined structural and stratigraphic approach based on the knowledge
about LU stratigraphy, represents a valuable tool for
the study of the Schistes Lustres ophiolitic units of the
Western Alps.
REFERENCES
- Burroni A., Levi N., Marroni M. & Pandolfi L. (2003).
Lithostratigraphy and structure of the Lago Nero Unit
(Chenaillet Massif, Western Alps): comparison with Internal Liguride Units of Northern Apennines. Ofioliti,
28, 1-11.
- Decandia F.A. & Elter P. (1972). La zona ofiolitifera
del Bracco nel settore compreso tra Levanto e la Val
Graveglia (Appennino Ligure). Mem. Soc. Geol. It., 11,
503-530.
- Elter P. & Raggi G. (1965) (a). Contributo alla conoscenza dell’Appennino ligure: 1)- Osservazioni preliminari sulla posizione delle ofioliti della zona di Zignago
(La Spezia). 2) Considerazioni sul problema degli olistostromi. Boll. Soc. Geol. Ital., 84, 303-322.
- Elter P. & Raggi G. (1965) (b). Contributo alla conoscenza dell’Appennino ligure: 3)- Tentativo di
interpretazione delle brecce ofiolitiche cretacee in
relazione con movimenti orogenetici nell’Appennino
ligure. Boll. Soc. Geol. Ital., 84 (5), 1-12.
- Elter G., Elter P., Sturani C. & Wiedmann M. (1966).
Sur la prolongation du domaine de l’Appennin dans
le Monferrat et les Alpes et sur l’origine de la Nappe
de la Simme s.l. des Préalps romandes et chaiblaisiennes. Arch. Soc. Phys. Nat. Genève, 19, 1002-1012.
- Elter P. & Pertusati P.C. (1973). Considerazioni sul
limite Alpi-Appennino e sulle relazioni con l’arco
delle Alpi occidentali. Mem. Soc. Geol. It., 12, 359375.
- Elter P. (1975) (a). Introduction à la géologie de
l’Apennin Septentrional. Bull. Soc. Geol. France, 17,
956-962.
- Elter P. (1975) (b). L’ensemble ligure. Bull. Soc.
Geol. France, 17, 984-997.
- Elter P. & Marroni M. (1991). Le Unità Liguri dell’Appennino Settentrionale: sintesi dei dati e
nuove interpretazioni. Mem. Descr. Serv. Geol. Italiano, XLVI, 121-138.
- Elter P. (1993). Detritismo ofiolitico e subduzione:
riflessioni sui rapporti Alpi e Appennino. Mem. Soc.
Geol. It., 49, 205-215.
- Lagabrielle Y. (1987). Les ophiolites: marquer de
l’histoire tectonique des domains oceaniques. Le
cas des Alpes franco-italiennes (Queyras, Piémont).
Comparaison avec les ophiolites d’Antalya (Turquie)
et du Coast Range de Californie. These de Doctorat
d’Etat, Univ. de Bretagne, 350pp.
- Loprieno A., Ellero A., Elter P. & Molli G. (2009).
Structural geometries and tectonic evolution of ophiolite and continental units in the Urtier Valley, Cogne
(Western Alps). 9th Alpine Workshop “AlpShop
2009”, Cogne, Italy.
- Loprieno A. & Ellero A. (2014). Structural analysis
of the nappe stack in the Urtier Valley, Cogne (Western Alps). Meeting in memory of Piero Elter. The relationships between Northern Apennine and western
Alps: state of the art fifty years after the “Ruga del
Bracco” Pisa, June 26-27, 2014.
- Marroni M. & Pandolfi L. (1996). The deformation
history of an accreted ophiolite sequence: the Internal
Liguride units (Northern Apennines, Italy). Geodin.
Acta, 9 (1), 13-29.
23
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
The Late-Variscan tectonic barriers:
the beginning of Alpine Wilson Cicle?
Franco Marco Elter(1), Laura Gaggero(1), Enrico Pandeli(2)
(1) DISTAV - Departement of Earth Science, Environment and Life, University of Genova, Italy
(2) Departement of Earth Science, University of Firenze, Italy
Recent studies suggest that the Variscan orogeny developed through a process of accretion of peri-Gondwanian
terranes (e.g. Avalonia, Armorica) and wider continental
masses (e.g. Baltica, Laurentia, and Laurussia, Padovano et al., 2012, 2014). The origin of the peri-Gondwanian terranes is linked to a continuous fragmentation of
the northern Gondwana margin which started, at least,
during the Cambrian with the opening of the Rheic
Ocean and the separation of Avalonia from. During Devonian time, the opening of Palaeotethys led to a further
fragmentation of the northern Gondwana margin, with
the formation of a narrow terrane known as the Hun superterrane or the Galatian ribbon continent. The closure
of the Palaeotethys and Rheic Oceans started at ~360
Ma, and led to the final collision and amalgamation of
Gondwana, Gondwana-derived continents, and Laurussia, with the formation of Pangea at ~300 Ma (Figure 1).
The continental collision involved plates characterized
by irregular boundaries, and thus resulted in a complex
pattern of coeval transpressional and/or transtensional
strike–slip shear zones (Figure 1, Elter et al. 2010, Elter
& Padovano 2010, 2013, Padovano et al., 2012, 2014).
The East Variscan Shear Zone (EVSZ, Padovano et al.,
2012, 2014) affected numerous Variscan massifs scat-
Figure 1
tered in the western Mediterranean area in the time interval 330–300 Ma .
The Gondwana continent is characterized by the presence, on the east, of the Paleotethys and by the Elbe
Shear Zone system (running from Boemia to Moesia)
while the western boundary is characterized of the
peri-Gondwanian terranes affected by intracontinental
strike-slip shear zones. The EVSZ, running from Slovenia to the Atlas system, is one of the major strike-slip
shear zone at present known (Padovano et al., 2012,
2014). We suggest that the EVSZ and the ESZ could
represent the tectonic lineaments (preexisting tectonic
barriers) along those, the opening of Piedmontese-Ligure Basin on the west and the new Tethys on the east
develop in the Permian-middle Jurassic time.
The opening of these two oceans can give the beginning
of the Alpine Wilson Cicle, involved in the Alpine Belt
(on the East - Dinaridi-Hellenides system, on the west
the Alps system).
REFERENCES
- Elter F.M. & Padovano M. (2013). Late Carboniferous Transpressional shear-zones in NE Sardinia (Italy): geodynamic implications. In: “Crustal melting
within the European Variscan belt”- BRGM-SGF-Orleans- France, 7.
- Elter F.M., Padovano M. & Kraus R.K. (2010). The
Variscan HT metamorphic rocks emplacement linked
to the interactiuon between Gondwana and Laurussia
plates: structural constraints in NE Sardinia (Italy). Terra Nova, 22, 369-377.
- Padovano M., Elter F.M., Pandeli E. & Franceschelli
M. (2012). The East Variscan Shear Zone: new insights
into its role in the Late Carboniferous collision in southern Europe. International Geology Review, 54, 8, 957970.
- Padovano M., Dorr W., Elter F.M. & Gerdes A. (2014).
The East Variscan Shear Zone: geochronological constraints from the Capo Ferro area (NE Sardinia, Italy).
Lithos 196-197, 27-41.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Olistostromes and mélanges in the External Ligurian Units
in Monferrato (NW Italy)
Andrea Festa(1), Gian Andrea Pini(2), Yildirim Dilek(3)
(1) Dipartimento di Scienze della Terra, Università di Torino, Italy
(2) Dipartimento di Matematica e Geoscienze, Università di Trieste, Italy
(3) Department of Geology and Environmental Earth Science, Miami University, Oxford, OH, USA
During 60’s and 70’s Piero Elter detailed worked and
described the olistostromes of the Northern Apennines,
introducing new terms (e.g. “endolistostrome” and “allolistostrome” of Elter and Raggi, 1965; “precursory
olistostrome” of Elter and Trevisan, 1973) and concepts
on their significance in the framework of the tectono-stratigraphic evolution of the Northern Apennines.
His research significantly influenced the subsequent literature on mélanges and olistostromes throughout the
world.
About 50 years later and strongly inspired from those
papers, we report the occurrence of olistostromes and
mélanges in the External Ligurian Units in Monferrato.
Following Elter et al. (1966), we describe in detail the
internal structure of the External Ligurian Units which
can be correlated with the Cassio Unit. Particularly, we
demonstrate that they consist of different polygenetic
chaotic bodies formed by the superposition of tectonic, diapiric and sedimentary processes which occurred
during the Late Cretaceous – late Oligocene tectonic
evolution of the Ligurian Accretionary Wedge (Festa et
al., 2013).
A Broken Formation is the oldest unit in the Ligurian Accretionary Wedge, showing bedding-parallel boudinage
structures, which developed as a result of layer-parallel
extension at the toe of the internal part of the Alpine
wedge front during the late Cretaceous–middle Eocene.
This Broken Formation experienced an overprint of tectonic, diapiric, and sedimentary processes as a result of
continental collision in the late Oligocene. Contractional deformation produced a structurally ordered block-inmatrix fabric through mixing of both native and exotic
blocks, forming a Tectonic Mélange. Concentration of
overpressurized fluids along thrust faults triggered the
upward rise of shaly material, producing a Diapiric
Mélange, which provided the source material for the
downslope emplacement of the youngest, late Oligocene Olistostromes (i.e., sedimentary mélange). The
Olistostromes unconformably cover the thrust faults,
constraining the timing of the youngest episode of
contractional deformation in the Ligurian Accretionary Wedge. The interplay and superposition of
tectonic, diapiric and sedimentary processes plays a
significant role in the dynamic equilibrium of accretionary wedges. Our findings provide useful criteria
to differentiate between different types of polygenetic mélanges in ancient and modern accretionary
wedges.
REFERENCES
- Elter, P., & Raggi, G. (1965), Contributo alla conoscenza dell’Apennino ligure: 1. Osservazioni preliminari sulla posizione delle ofioliti nella zona di Zignago
(La Spezia); 2. Considerazioni sul problema degli olistostromi. Bollettino della Società Geologica Italiana,
84, 303–322.
- Elter, P., & Trevisan, L. (1973), Olistostromes in the
tectonic evolution of the Northern Apennines. In K.A.
De Jong, & R. Scholten (Eds.), Gravity and tectonics
(pp. 175–188). New York, John Willey and Sons.
- Elter, G., Elter, P., Sturani, C., & Weidmann, M. (1966),
Sur la prolongation du domaine ligure de l’Apennin dans
le Monferrat et les Alpes et sur l’origine de la Nappe de
la Simme s.l. des Préalpes romandes et chablaisannes.
Archives des Sciences de Genève, 19, 279–377.
- Festa A., Dilek., Y., Codegone G., Cavagna, S., & Pini,
G.A. (2013), Structural Anatomy of the Ligurian Accretionary Wedge (Monferrato, NW-Italy), and Evolution of
Superposed Mélanges. Geological Society of America
Bulletin, 125 (9/10), 1580-1598.
25
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Ductile shear zone in the thermo-metamorphic aureole of Monte Capanne: data from Cavoli-Colle Palombaia area (South-western Elba Island,
Italy)
Riccardo Giusti(1), Enrico Pandeli(1,2), Franco Marco Elter(3)
(1) Department of Earth Sciences, University of Florence, Italy
(2) CNR-Institute of Geosciences and Georesources, Section of Florence, Italy
(3) DISTAV, University of Genoa, Italy
The Elba Island is located in the Northern Tyrrhenian
Sea at midway between Tuscany (Northern Apennines
Chain) and Corsica (Alpine Corsica structural pile).
The complex Elba Island stack of nappes, which is considered the innermost outcrop of the tertiary Northern
Apennines Chain, is also well known for its Fe-ore bodies and the relationships between the emplacement of
the Mio-Pliocene acidic magmatic bodies and tectonics
(Bortolotti et alii 2001). The emplacement of the acidic
plutons caused the thermal metamorphism in the host
units (oceanic Ligurian and Piedmontese and continental Tuscan units) and remobilized the original tectonic
stacking of the nappes. In particular the plutons caused
deformations in both brittle and ductile regime in the
surrounding units (e.g. detachements and foldings,
BORTOLOTTI et alii 2001 and references therein).
The plutonic complex of Monte Capanne (6.9 Ma Dini
et alii, 2002), which dominates the western part of the
island (Fig.1), was emplaced in the Upper Jurassic-Lower Cretaceous ophiolitic successions (Bortolotti et alii
2001), after the intrusion of acidic dikes and laccoliths
(“Christmas-tree” laccolithic complex, Dini et alii,
2002: 8-8.5 Ma Capo Bianco Aplite, 8 Ma Portoferraio
Porphyry and 7.4-7.2 Ma San Martino Porphyry).
The rocks of M. Capanne aureole show different thermal metamorphic imprint ranging from high to low
grade in the different parts of the “ring”, as a function
of distance from the pluton and of the circulation of
fluids. Locally, an anomalous increase of metamorphic
grade is evident and can be likely related to variation
of permeability in the host rocks for the ascent of the
metasomatic fluids.
Furthermore in the Fetovaia Promontory area, the
un-metamorphic Eocene Fetovaia Flysch unit tectonically lies above the metamorphosed ophiolitic successions. This tectonic attitude is related to brittle low-angle detachements occurred in the cover units of the
pluton during its uplift, as it is well known in central
Elba for the eastward sliding of the Marina di Campo
Fm. (CEF, Maineri et alii, 2003). Subsequently, these
rocks have been displaced by high-angle normal faults
(e.g. EBF, Maineri et alii, 2003). In any case, the primary relationships between intrusive bodies and their
covers are often evident in many places, as well as the
Fig. 1 - Geological sketch map
of Western Elba Island
26
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
evidence of polyphasic both ductile and brittle tectonic
activity due to the different evolutive stages of emplacement of the pluton. In the thermo-metamorphosed ligurian units, the ductile deformation occurred especially
within the carbonate lithologies, while the pelitic lithologies show basically a brittle behavior, coherently with
static recrystallization phenomena.
The paper presents for the first time data on the ductile
shear zone found in the ophiolitic units of Cavoli-Colle Palombaia outcrops, with the development of mylonites, decimeter to plurimetric in thickness, consisting
mainly of crystalline carbonate foliated bodies (derived
from the Calpionelle Limestones) in which enclaves of
meta-cherts and meta-basalts are present.
The analysis, performed on the kinematic indicators
(e.g. σ and δ type porphyroclasts, asymmetric folds and
domino structures) and fold structures, show that the
main direction of the mylonitic foliation and the shear
sense are connected with a transport towards the outside
of the intrusive massif of M. Capanne. In particular the
direction of movement is towards ESE. So, the location
of the outcrops with respect to the main body of the pluton of M. Capanne is consistent with a radial pattern of
the stress field. This radial trend is a typical feature of
the discharge phenomena related to the up-rising of a
sub-spherical body.
In several outcrops of the mylonite it is evident the presence of different deformation regimes, both simple shear
and pure shear. Locally the occurrence of the combination of the two end-member (sub-simple shear) testify
the extreme variability and complexity of the processes
at the time of the development of shearing.
Furthermore, the microscopic analysis point that the
foliation and associated microstructures are related to
metamorphic events of medium to high grade (HT-LP)
linked to the dynamo-thermal effects of the M. Capanne
pluton emplacement.
REFERENCES
- Bortolotti V., Fazzuoli M., Pandeli E., Principi G.,
Babbini A. & Corti S. (2001), Geology of the central
and eastern Elba Island, Italy. Ofioliti, 26 (2a), 97-150.
- Dini A, Innocenti F., Rocchi S., Tonarini S. & Westerman D.S. (2002), The magmatic evolution of the late
Miocene laccolith-pluton-dyke granitic complex of Elba
Island, Italy. Geological Magazine, 139, 257-279.
- Maineri C., Benvenuti M., Costagliola P., Dini A., Lattanzi P, Ruggieri G. & Villa I.M. (2003), Sericitic alteration at the La Crocetta deposits (Elba Island, Italy):
interplay between magmatism, tectonic and idrotermal
activity. Mineralium Deposita 38, 67-86.
27
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
The role of the Ottone-Levanto line in the geodynamic evolution of the
Northern Apennine: evidences from the high Sturla Valley, Liguria, Italy
Noah Hobbs, Edoardo Luvisi, Michele Marroni, Francesca Meneghini, Luca Pandolfi
Dipartimento di Scienze della Terra, Università di Pisa, Italy
In the Northern Apennine, the structural setting is represented by a pile of tectonic units assembled from
different pelogeographic domain during the closure of
the Ligure-Piemontese oceanic basin and the following
continental collision. This pile is cut by several high-angle shear zones of regional extent, showing different kinematics, age and geodynamic role.
Among these lines, the Ottone-Levanto line (Elter and
Pertusati, 1973) is regarded in literature as one of the
most important structural element that played a fundamental role in the geodynamic evolution of the Northern
Apennine, at its junction with the Western Alps. Despite
its importance, no meso- and microstructural data are
available in order to constrain the kinematics of the Ottone-Levanto line.
A shear zone representative of the deformation along
the Ottone-Levanto line has been identified in the high
Sturla valley (Liguria). In the field, the shear zone is represented by 5 to 15 m thick foliated cataclasites, associated with meter thick bodies of unfoliated cataclastic
serpentinites.
The foliated cataclasites originated from the brittle dismemberment of an assemblage of peridotites, gabbros,
granites. They display a crude mesoscopic layering defined by the alternation of mm- to cm-thick bands of
different colours, from green to dark grey. Bands display
locally an anastomosing network, and are often characterized by a sharp thickness reduction along their length.
The dark grey bands show a fine-grained, homogenous
granular texture, whereas the green ones consist of
matrix-dominated rocks where mm to cm size angular
fragments of serpentinites, limestones and gabbros are
floating in a fine-grained matrix with well-developed
penetrative foliation. Foliation surfaces dip toward the
SW, and show a strike ranging from N30°/N40° to N80°/
N90°, as a result of a deformation by NW-SE trending
folds with gently dipping axial plane. More over, the foliated cataclasites show an internal deformation by open
to close folds with E-W trending axes that does not affect the surrounding lithotypes. In the NW-SE striking
and SW dipping foliated cataclasites, the facing of these
folds indicate a top-to-the SE sense of shear.
The cataclastic unfoliated serpentinites occur as meter-thick dark green bodies characterized by a complex
network of quartz veins. These bodies, even if massive,
reveal a rough banding of thick levels, featuring relics
of pyroxene, and a poorly modified peridotite primary
structure, alternating with levels showing a strong grain
size reduction.
The structural analysis at meso-scale indicates a deformation involving components of contraction with topto-the-NE thrusting, and contemporaneous top-to-theSW sinistral shearing and dip-slip shearing.
At the micro-scale, the foliated cataclasites are characterized by elongated, angular to sub-rounded clasts of
serpentinite, and subordinately calcite, both deriving
from the rock types characterizing the hanging wall and
footwall units. Serpentinite clasts are generally asymmetric with δ-type shapes, and the asymmetry is evidenced by pressure shadows at clasts edges defined by
re-crystallization of micro-crystalline quartz. In oriented samples, the clasts asymmetry is indicative of a sense
of shear toward the eastern sectors. Calcite in the clasts
is characterized by thin and thick, regular straight twins,
ascribable to the Type I and II twin morphology classes
of Burkhard (1993) and Ferrill et al. (2004). The foliation of the cataclasites is a planar anisotropy defined by
the millimeter-scale alternation of phyllosilicate layers
and granoblastic quartz-rich layers. Phyllosilicates layers are made by chlorite crystals preferentially oriented
parallel to banding to define the foliation. Granoblastic
layers are characterized by re-crystallized fine- to very
fine-grained quartz crystals that are frequently associated with microcrystalline serpentine and calcite. Chlorite
also occurs as an alteration product of the serpentinite
clasts, whereas calcite is also found in veins possibly
related to alteration and fracturing of the serpentinite.
Quartz is dominantly affected by intracristalline deformation (mainly undulose exctintion), but commonly
shows as well evidence of dynamic recrystallization.
These data coupled with regional evidences suggest that
the Ottone-Levanto line can be regarded as a sinistral
28
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
traspressional shear zone developed in the Late Eocene-Early Oligocene time. The line can be thus correlated with others lines of the Alpine-Apennine system, as the Insubric Fault, the Sestri-Voltaggio line and
the Central Corsica shear zone. All these lines devel-
oped during the collisional tectonics resulting in both
east- and westward thrusting of the internal zone of the
appennine-alpine belt onto the continental margin domains, coeval with the northward displacement of the
Adria plate.
29
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Distribution of differing stress regimes in the Western Central Alps
controlled by inner arc bending?
Kraus R.K.(1), Elter F.M.(1), Elena E.(2), Solarino S.(2)
(1) DISTAV, University of Genova, Italy
(2) INGV, Genova, Italy
The slightly N-S bent Western Alps, with the adjacent Po
Plain and Ligurian Sea are characterized by many seismic events. The pattern of earthquakes shows various
patterns: arcuate, cluster and random distribution. We
observe on the basis of the distribution of focal mechanisms 5 zones with different stress regime: the Western
Seismic Arc (Briançonnaise-Arc), the Eastern Seismic
Arc (Piedmont-Arc), the area SW from Turin in the Po
Plain, the French/Italian Coastline (also Mediterranean
Alps) and the E-W trending arm of the Ligurian Sea.
The Briançonnaise-Arc is characterized by shallow
crustal seismicity up to 15 km of depths, which affects
especially the brittle sedimentary sequences. The focal mechanisms show a transtensive stress field for the
Western Seismic Arc. The seismic events in the Piedmont-Arc occur from shallow to middle crust up to 30
km of depth and seem to follow the western edge of the
“Ivrea Body” (a fragment of deeper crust). The stress
field suggested by focal mechanisms is transpressive at
shallow level with an increasing compressional component with depth. In between those two seismic arcs is a
zone with considerably less seismic activity. In the area
SW from Turin in the Po Plain is a cluster of subcrustal
events with up to 70 km of depth. According to literature, this zone inhabited the rotation pole of the Adrian
microplate and thus represents a place in which the European, Adrian and Ligurian domains meet.
The French/Italian Coastline is represented by many
seismic events up to middle crust, of mainly transtensive and strike-slip character. The E-W trending Ligurian Sea instead is dominated by strike-slip, thrust and
transpressive events, which confirm the closure of the
Ligurian Sea, as already observed by various authors.
In literature is described that in the inner arc of a bent
mountain belt the strain ellipses display arc-.parallel
shortening and thickening of the mantle lithosphere,
whereas the outer arc is dominated by arc-parallel
stretching accompained by crustal thinning. In between is a neutral zone, in which the forces annihilate
each other. This is in agreement with the observations
in the arcuate-shaped Western Alps: the External Alps
are prone to oblique extension and shallow seismicity, whereas the Internal Alps submit to transpressional
forces and mid-crustal seismicity. The neutral surface
is in agreement with the position of the “Ivrea Body”,
using the neutral zone for intrusion. As in the case of
the Western-Central Alps the Apenninic indenter is advancing, part of the accumulated stress gets dissipated
along oblique normal and strike-slip faults leading to
lateral extrusion of the French/Italian Mediterranean
Alps towards SE. This explains the closure of the E-W
trending arm of the Ligurian Sea and is in agreement
with the observed principle horizontal stress vector in
NW±SE direction in literature.
30
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Structural analysis of the nappe stack in the Urtier Valley,
Cogne (Western Alps)
Andrea Loprieno(1), Alessandro Ellero(2)
(1) Viale Cavagnet 45, Cogne, Aosta, Italy
(2) CNR-IGG, Pisa, Italy
In this contribution we summarize the main results of structural investigations originally performed during diploma
theses in the Urtier Valley, an area located at the northern
flank of the Gran Paradiso Massif.
Five different tectonic units were mapped in the area, from
the geometrically lowermost to the uppermost they are: 1)
the Gran Paradiso basement unit mainly composed of late
Variscan granitoids and metapelites; 2) the Péne Blanche
unit (part of the so-called “Fasceaux de Cogne”) which comprises Triassic quartzites, dolomites and carbonates and Liassic calcschists; 3) the oceanic Broillot unit including ophiolites and their metasedimentary cover; 4) the Bardonney
mélange unit (BM) with ophiolites only represented in clasts
and/or slices from centimeter to pluridecameter in size within an abundant carbonate/quarzitic and/or metabasic matrix;
5) the continental basement slices of Tour Ponton and Acque
Rosse units.
The structural evolution of the Urtier Valley is characterized
by three major deformation phases and related structures affecting all tectonic units (Loprieno et al., 2009).
D1 structures are represented by relict microfabric associated with eclogite-facies assemblages and small-scale isoclinal folds. It is also responsible for early stage of nappe stack
formation. More problematic is the recognition of the D1
metamorphic grade in the BU. Overall it shows a blueschist
facies metamorphism, similarly to what described for this
unit outside of the study area (e.g. Colle della Rosa Dondena
Unit by Battiston et al., 1984). However, high pressure assemblages have been recently recognized within garnet and
chloritoid micaschists (Beltrando et al., 2008), suggesting an
eclogitic facies metamorphism also for the BU.
D2 is the dominant deformation stage, refolding the tectonic
contacts between the units, showing D2 isoclinal folds on
all scales, associated with S2 greenschist facies pervasive
mylonitic fabric that represents the main foliation at regional
scale. D2 folds axes and L2 lineation show a common orientation with E-W trend.
D3 is instead characterized by open to close folds with NE
or SW gently dipping axial plane that refold the composite
main foliation S1/S2.
At the scale of the study area, the reconstruction of the general architecture of the stacked units is facilitated by strati-
graphic markers within the ophiolitic units (Ellero &
Loprieno, 2014), showing how the nappe pile as a
whole is deformed by a D2-D3 interference structure,
with a large scale D2 synform refolded by a large scale
D3 Urtier antiform. We suggest that this structure can
be interpreted as the eastern closure of the Valsavarenche mega-fold, the so-called “Valsavaranche backfold” of Argand (1911) within the schistes lustres units,
representing an extension of the structures described in
adjacent areas by Bucher et al. (2003).
REFERENCES
- Argand E. (1911). Sur les plissements en retour et la
structure en éventail dans les Alpes occidentals. Bull.
Soc. Vaud: Sc. Nat., XLVII.
- Battiston P., Benciolini L., Dal Piaz G.V., De Vecchi G., Marchi G., Martin S., Polino R. & Tartarotti P.
(1984). Geologia di una traversa dal Gran Paradiso alla
Zona Sesia-Lanzo in alta Val Soana, Piemonte. Mem.
Soc. Geol. It., 29, 209-232.
- Beltrando M., Lister G., Hermann J., Forster M. &
Compagnoni R. (2008). Deformation mode switches in the Penninic units of the Urtier Valley (Western
Alps): evidence for a dynamic orogen. J. Struct. Geol.,
30, 194-219.
- Bucher S., Schmid S.M., Bousquet R. & Fügenschuh
B. (2003). Late-stage deformation in a collisional orogen (Western alps): nappe refolding, back-thrusting or
normal faulting? Terra Nova, 15, 109-117.
- Loprieno A., Ellero A., Elter P. & Molli G. (2009).
Structural geometries and tectonic evolution of ophiolite and continental units in the Urtier Valley, Cogne
(Western Alps). 9th Alpine Workshop “AlpShop
2009”, Cogne, Italy.
- Ellero A. & Loprieno A. (2014). Ophiolitic units of
the Northern Appenines as a tool to unravel Schistes
Lustres stratigraphy of the Western Alps and their geodynamic context: the Urtier valley example, Cogne,
Aosta Valley. Meeting in memory of Piero Elter. The
relationships between Northern Apennine and western Alps: state of the art fifty years after the “Ruga del
Bracco” Pisa, June 26-27, 2014.
31
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Zircon (U-Th)/He dating of the Penninic basal thrust
Matteo Maino(1), Finlay M. Stuart(2), Andrea Ceriani(1,3), Alessandro Decarlis(4), Andrea Di Giulio(1),
Silvio Seno(1) and Massimo Setti(1)
(1) Dipartimento di Scienze della Terra e dell’Ambiente, Università di Pavia, Italy
(2) Isotope Geosciences Unit, SUERC, Scottish Enterprise and Technology Park, East Kilbride,UK
(3) The Petroleum Institute, Abu Dhabi
(4) IPGS/EOST, Strasbourg, France
We presents new zircons (U–Th)/He (ZHe) ages from
the thrust fault damage zone and surrounding wall rocks
to determine the emplacement age of the southernmost
segment of the Penninic basal thrust. Thermocronometry is integrated with X-ray diffraction analysis of clay
minerals (illite crystallinity) and fluid inclusion microthermometry on vein-filling minerals to constrain the
temperature conditions of the damage zone and the wall
rocks during thrusting. This approach has been applied
to the basal thrust of the Helminthoid Flysch, which represents the tectonic front of the European Alps accretionary wedge (Maino et al., 2013). Zircons selected for
He dating are from Early Cretaceous arkosic sandstones
the base of which has been involved into the thrust zone.
ZHe ages of the fault rocks are completely reset
(28.8±3.4 to 33.8±4.0 Ma) while the wall rock samples show pre-depositional inherited ages (117.4±14 to
158.7±18.9 Ma). Thermal constraints support warmer
conditions (~220-300°C) within the fault damage zone
respect to the wall rocks (< ~200°C), with the presence
of a transition zone corresponding to a gradual increase
of ZHe ages at progressive distance from the top of
the fault damage zone. These results are in excellent
agreement with the available independent geological
and thermochronometric constraints that support early Oligocene movement of the basal thrust of the Helminthoid Flysch (Ford et al., 1999; Maino et al., 2012;
Decarlis et al., 2013). Our results underscore, for the
first time, the validity of ZHe tecnhique as a reliable
thermochronometer to dating brittle faults developed
into shallow crustal levels (< 6-7 km) on geological
timescales.
REFERENCES
- Decarlis, A., Dallagiovanna, G., Lualdi, A., Maino,
M. and Seno, S. (2013). Stratigraphic evolution in
the Ligurian Alps between Variscan heritages and the
Alpine Tethys opening: a review. Earth-Science Reviews, 125, 43-68.
- Ford, M., Lickorish, W.H. and Kusznir, N.J. (1999).
Tertiary Foreland sedimentation in the Southern Subalpine Chains, SE France: a geodynamic appraisal.
Basin Research, 11, 315-336.
- Maino, M., Dallagiovanna, G., Dobson, K., Gaggero, L., Persano, C., Seno, S. and Stuart, F.M. (2012).
Testing models of orogen exhumation using zircon
(U–Th)/He thermochronology: insight from the Ligurian Alps, Northern Italy. Tectonophysics, 560-561,
84-93, doi:10.1016/j.tecto.2012.06.045.
- Maino, M., Decarlis, A., Felletti, F., Seno, S. (2013).
Tectono-sedimentary evolution of the Tertiary Piedmont Basin (NW Italy) within the Oligo–Miocene
central Mediterranean geodynamics. Tectonics, 32, 3,
593-619, DOI: 10.1002/tect.20047.
32
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Impact of surface processes and structural heritage on the structure and
dynamics of orogenic wedges : Insights from Taiwan
Jacques Malavieille
Université Montpellier 2, CNRS UMR 5243, Lab. Géosciences Montpellier, France
and LIA-ADEPT 536 CNRS-NSC, France-Taiwan
As mountain belts are long lived structures, their evolution involves numerous processes that interact since the
early history, beginning during oceanic subduction and
ending during the late orogenic evolution, which leads
to erosion and the ultimate destruction of topography.
Most orogens form in subduction settings due to plate
convergence involving large horizontal shortening and
strong deformation of the crust developing into an overall wedge shape during their evolution. I will focus on
the Taiwan orogen caused by the subduction of a continental margin lower-plate under an oceanic upper-plate
bearing a volcanic arc following intra-oceanic subduc-
Figure 1
tion, a process commonly known as arc-continent collision. Thus, after the development of a sedimentary
accretionary prism and closure of the oceanic domain,
continuous subduction of the lithospheric mantle induces deformation of the continental crust and controls
the structural asymmetry of the growing mountain belt.
Since the pioneer works by Dahlen, Davis and Suppe in
the Eighties, mountain belts have been often considered
by geologists as crustal scale accretionary wedges whose
deformation mechanisms can be satisfactorily described
by a Coulomb behavior. The theory offers a simple mechanical framework allowing a division into different
tectonic regimes depending on wedge stability : critical,
undercritical, overcritical. Since then, it has been shown
that orogens commonly adopt a distinct geometry with a
low-tapered pro-wedge facing the subducting plate, and
a high-tapered retro-wedge on the internal side. Erosion
has rapidly been added as a significant parameter because the impact of material transfer on the mechanics
and structural evolution of sub-aerial wedges relative to
submarine ones is major.
In the active Taiwan orogen major questions can be
addressed concerning; mechanisms of lithospheric deformation in convergent settings, subsequent active
deformation involving large seismogenic faults, processes of mountain building (from oceanic subduction
to continental subduction and late orogenic extension)
and impact of surface processes. In this area, the obliquity of the plate convergence involves the progressive
subduction of the continental margin of China inducing
the fast growth of the mountain belt. Today, the orogen
culminates at about 4000 meters rising from sea-level
a few million years ago. Impact of climate and surface
processes are thus particularly well expressed allowing to study their interaction with tectonic processes
in the island which is particularly vulnerable to natural
hazards (one of the highest population densities in the
world). Because of the high convergence rate (~ 9 cm/
yr) and the complex interaction (doubly-verging oceanic and continental subduction) between converging
Eurasia and Philippine Sea plates (PSP), deformation
33
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Figure 2
rates and erosion rates are extreme (horizontal shortening > 2 cm/yr on major faults, vertical motions up
to 3 cm/yr). In the domain of active continental subduction, where the orogenic wedge grows today, estimates of middle-term shortening rates on active faults
as well as deformation mechanisms in the wedge show
a surprising behavior. Most of the convergence is accounted for by just a few major faults, on the western
side of the wedge in the foreland and on its backside
against the Philippine sea upper-plate onland along the
Longitudinal Valley and offshore the Coastal Range, the
accreted part of the Luzon Volcanic arc. Thus most of
the bulk shortening occurs today on foreland faults and
along the backside of the mountain belt, leaving little (if
any) horizontal shortening within the body of the wedge
(Fig. 1). Together with new constraints on the thermal
evolution and exhumation of the metamorphic Central
Range (CR), this kinematic has been analyzed by numerical thermo-kinematic and analog models involving erosion, in which underplating at depth sustains the
growth of the orogenic wedge. Results of models show
that interactions between tectonics and surface processes play a major role in controlling relief morphology,
fault evolution, uplift inside the orogen and localization
of exhumation. The main processes of wedge growth
in Taiwan can be described by accretion in the frontal
part of the thrust wedge and underplating of tectonic units at depth under the Central Range, involving
strong uplift and thickening of the internal domain and
backthrusting on the PSP upper-plate. Thus, intermediate-term deformation is strongly partitioned in Taiwan
suggesting important insights on the present-day behavior and growth mechanisms for large faults that are
responsible for great earthquakes (Fig. 2).
Following this regional approach, I will address major open questions regarding the global and local responses (i.e., at orogenic scale and at the scale of faults
or ridges) of an orogenic wedge under the impact of
tectonic or climatic forcing at different time scales.
Insights from analog models are used to; - illustrate
the impact of first order parameters such as the initial
geodynamic subduction setting, material transfer in
the wedge, structural inheritance (OCT and inherited
extensional structures), - show how the interactions
between surface processes and tectonics influence the
structures and the behavior of orogenic wedges (kinematics of deformation, exhumation mechanisms, and
long-term evolution). Finally, analogies between the
evolution of Taiwan orogen and the evolution of the
Alps-Apennine geodynamic system will be outlined,
foregrounding the key role of continental subduction
and subduction reversal.
34
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
The basal part Modino Unit Succession under the belt-foredeep system
of the Northern Apennines (Italy)
Alessandra Marchi(1), Luca Pandolfi (1, 2), Rita Catanzariti(2)
(1) Earth Science Department, Pisa University, Italy
(2) IGG-CNR Pisa, Italy
The Modino Unit turbidite system of the Northern
Apennines foreland basin provides an excellent opportunity to study the sedimentary and structural variations
within the context of spatial and temporal distribuition
of source rocks during the evolution of foreland basins.
The substrate of this Unit was interpreted as a stratigraphic-structural mélange (Plesi et al., 2000), the expression
of polyphase tectonic phases of Cretaceous-Eocene accretion that have affected the external part of Ligurian
and Subligurian domain.
In this article we present the preliminary data of different stratigraphic sections outcropping in Tuscan and
Emilian regions, with particulary attention to the lower
part of Modino Unit Succession, of pre-Ligurian stage,
unconformably deposited at the top of the Ligurian and
Subligurian substrate, composed by Fiumalbo Shale
Fm. and Marmoreto Marl Fm.
The tectonic setting of this Unit is complex and necessitated the use of stratigraphical, biostratigraphical and
petrographical studies to achieve this goals.
The Modino Unit succession is composed by three different formations:
The Fiumalbo Shale Fm. followed in some sections of
coarse breccia deposits that cover the substrate (Riccovolto Breccia) are made up of mostly red and green
shales with intercalations of limestone and turbidite-like
sandstones beds more or less extensive (Rio Acquicciola
Sandstones Auctt. or M. Sassolera Sandstones Auctt.).
The Marmoreto Marl Fm. are characterized by fine emipelagic sediments, have a massive structure (with rare
thin layers of fine sandstones).
The Monte Modino Sandstone Fm. are constituted by
one or more sequences of turbidite facies with quite
variable vertically and laterally . Their deposition occurs
preferentially in the middle and front al part of the prism
and is quickly interrupted, on its southwestern margin,
by the thrust belt materials. From this reason the axis of
sedimentation moving outwards.
A petrographical study on turbidite-like sandstone beds
in Fiumalbo Shale Fm., show a petrofacies character-
ized by a modal composition of Q48F27L+CE25, according with the composition of Monte Modino Sandstone of this study, while shows different composition in
the Fine-Grained Rock Fragments Compositional Mode
(Lm-Lv-Ls plot).
The sandstones in Fiumalbo Shale Fm., are composed
by different tipology of fine grained lithic fragments,
and its composition changes strata-strata in the same
stratigraphic sections. The fine grained lithic fragments
are composed by dominating metamorphic origin clasts
and ophiolithic rock fragment associated with unmetamorphic radiolaritic fragments.
The biostratigraphical analysis indicate that the age of
these formations is comprised between Lutetian and
Chattian ages.
These formations reflect a slope environment, with
quite deep and with a strong affinity to Epiligurian
sections, which resemble the coeval succession Monte
Piano-Ranzano and their sedimentation environment
reflects a time and an area of major physiographic expression of the prism.
The composition of this arenites is interpreted as being
controlled mainly by synsedimentary tectonics connected with the evolution of an accretionary prism east vergent.
This composition reflects the different stages of the process of accretion and is the expression of the different
sedimentary environments that were gradually generating. The lower part of Modino Unit succession seems
to be supplied by two different source areas, the classic Alpine source area and a more proximal “Liguride
derived” source, maybe located in the proto-apenninic
wedge.
REFERENCES
- Plesi G., Chicchi S., Daniele G. & Palandri S. (2000).
La Struttura dell’Appennino reggiano-parmense fra
Valditacca, il Passo di Pradarena e il M. Ventasso. Boll.
Soc. Geol. It., 119, 267-296.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
The late Carboniferous-Permian successions of the Northern Apennines:
new data from the contact between San Lorenzo Schists and Asciano
Breccias and Conglomerates in the Pisani Mts. inlier (Tuscany, Italy)
Marini F.(1), Pandeli E. (1,2) & Tongiorgi M.(3)
(1) Earth Sciences Department, University of Florence, Italy
(2) CNR-Institute of Geosciences and Georesources, Section of Florence, Italy
(3) Natural History Museum, University of Pisa, Italy
The Pisani Mts is tectonic window allowing the exposure of the deepest metamorphic tectonic units of the
Northern Apennines chain. The Pisani Mts. metamorphic inlier is made up of two tectonically superimposed
tectonic sub-units (i.e the M.Serra and S.Maria del Giudice sub-Units) and it is laterally bounded by high-angle
normal faults. As in the other Tuscan inliers, the Pisani
Mts. successions includes a Paleozoic “basement” here
are represented by the Buti banded phyllites and quartzites (Upper Ordovician?), San Lorenzo schists (SLs, Upper Carboniferous-Early Permian) and Asciano breccias
and conglomerates (Abc, Permian?) that are separated
by erosional angular unconformity contacts at map scale
(Rau & Tongiorgi, 1974; Pandeli et al., 1994).
According to its sedimentological features and to the
abundant fossil floristic assemblage of Wephalian?/
Stephanian to Autunian time interval, previous Authors
suggested that the essentially grey to black siliciclastics of SLs were deposited in a mostly fluvio-lacustrine
environment characterized by reducing conditions, but
neritic faunal associations has been recently discovered
in the middle-lower part of the formation (Rau & Tongiorgi, 1974; Landi Degl’Innocenti et alii, 2008). The unfossiliferous Abc is represented by dominant purplish,
polymictic rudites. These poorly-mature and -sorted
sediments has been associated to fluvial-fan deposits
in a semi-arid environment (Rau & Tongiorgi, 1974).
The sharp and erosional stratigraphic contact between
SLs and Abc had been previously interpretated as the
angular unconformity of the Permian extensional rejuvenation event of the Variscan Chain in Europe (Saalian
event).
For improving the knowledge of this important Permian event in Tuscany from a paleogeographic, paleoenvironmental and paleotectonic point of view, the Authors carried out new studies about the SLs and Abc in
the Pisani Mts.. In this frame, the Authors analized a
well-exposed, continuous section containing the SLsAbc contact along the road to Pian della Conserva lo-
cality (see Fig. 1). In this place, We measured a detailed
lithostratigraphic section (132 m of total lenght) and
sampled the lithotypes for geochemical (main elements
through X-ray fluorescence technique) and microscopic
(textural and modal) analyses.
The studies reveal that the SLs/Abc contact in the Pian
della Conserva Section is gradual and it is characterized by passage for alternations of the lithotypes of
both formations. In particular, the top of SLs consists
of an alternance of thick grey to black metapelitic beds
with quartzitic metasandstone intercalations and rare
quartz-rich microconglomeratic beds: the latter become
more frequent, coarser and thicker towards the top of
SLs, where thin green phyllitic levels and a volcanoclastic layer also occur. The transition is represented by
an about 20 m-thick alternation of varicoloured (mostly
green) phyllitic lithotypes with greenish-grey metasand-
Figure 1 - Structural sketch of the Pisani Mts. (modified from
Rau & Tongiorgi, 1974). The asterisk indicates the location
of the studied outcrop, i.e. Pian della Conserva section.
36
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
stone and fine-grained metarudites. The Abc basal part
is made up of the same greenish metasiliciclastics but
with decimetric to metric intercalations of violet and
purple polymictic metabreccias and low-mature metaconglomerates and metapelites. Upward these two latter
lithotypes largely prevail. The passage between the two
formations is outlined not only by the cromatic change,
but also by petrographic-geochemical data that demonstrate a change from a reducting to a oxiding environment (e.g. the clear variation of LOI content and of
Fe2+/Fe3+ ratio).
The following results of the study can be pointed out:
1) Because of the gradual stratigraphic passage, the
unfossiliferous Abc can be likely attributed to Permian
(late Early Permian?); 2) The lithological-sedimentological data confirm that the SLs/Abc contact define the
tectonic rejuvanation of the Variscan landscape during
the Saalian Event, but also show a gradual change in
the climatic (from humid to semi-arid) conditions. This
can be related to the modification of the landscape (onset of new tectonic barriers) and of the drainage (from
fluvial valleys characterized by more or less wide, often
marshy flood plains to very active alluvial fans set close
to tectonic highs due to the Saalian strong rejuvenation
of the relief); 3) The presence of volcanic layers in the
Late Carboniferous-Autunian Sls has been pointed out
for the first time and show similarities with the metavolcanites (Iano porphiritic schists) present at the top
and interbedded within the Torri breccia and conglomerate (that corresponds to Abc) in the Iano Carboniferous-Permian succession (Pandeli, 1998).
REFERENCES
- Landi Degl’Innocenti V., Pandeli E., Mariotti Lippi M.
& Cioppi E. (2008) - The Carboniferous-Permian succession of the Pisani Mountains (Tuscany, Italy): preliminary data from the De Stefani collection (Natural
History Museum of Florence). Boll. Soc. Geol. It., vol.
127 n° 3, 548-558
- Pandeli E. (1998) - Permo-Triassic siliciclastic sedimentation in the Northern Apennines: new data from the
Iano metamorphic inlier (Florence). Mem. Soc. Geol.
It., 53, 185-206.
- Pandeli E., Gianelli G., Puxeddu M. and Elter F. M.
(1994) - The Paleozoic Basement of the Northern Apennines: stratigraphy, tectono-metamorphic evolution and
alpine hydrothermal processes. Memorie Società Geologica Italiana, 48, 627-654.
- Rau A. & Tongiorgi M. (1974) - Geologia dei Monti
Pisani e SE della Valle del Guappero, Mem. Soc. Geol.
It., 13, 227-408
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state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Thermo-mechanical numerical model of the transition from continental
rifting to oceanization: the transition from Permian-Triassic thinning to
oceanisation in the alpine chain
Anna Maria Marotta(1), Katya Conte(1), Manuel Roda(2), Maria Iole Spalla(1, 3)
(1) Department of Earth Sciences “Ardito Desio”, Università degli Studi di Milano, Italy
(2) Universiteit Utrecht, Fac. of Geosciences, Utrecht, Italy
(3) CNR-IDPA, Milano, Italy
The transition from continental rifting to oceanization
has been investigated by mean of a 2D thermo-mechanical numerical model in which the formation of oceanic
crust and serpentinite, due to the hydration of the uprising peridotite, as been implemented.
Model predictions have been compared with natural
data related to the Permian-Triassic thinning affecting
the continental lithosphere of the Alpine domain, in order to identify which portions of the present Alpine belt,
preserving the imprints of Permian-Triassic high temperature (HT) metamorphism, is compatible, in terms of
lithostratigraphy and tectono-metamorphic evolution,
with a lithospheric extension preceding the opening of
the Ligure-Piemontese oceanic basin. The HT Permian-Triassic metamorphic re-equilibration overprints an
inherited tectonic and metamorphic setting consequent
to the Variscan subduction and collision, making the
Alps a key case history to explore mechanisms responsible for the re-activation of orogenic scars.
Our comparative analysis supports the thesis that the
lithospheric extension preceding the opening of the Alpine Tethys did not start on a stable continental lithosphere, but developed by recycling part of the old Variscan collisional suture.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Lower Miocene contractional shearing in the Massa Unit
(Northern Apennines, Italy): in situ U-Th-Pb dating of monazite
Chiara Montomoli (1), Rodolfo Carosi (2), Antonio Langone (3), Angelo Borsani (4), Salvatore Iaccarino (1)
(1) Dipartimento di Scienze della Terra, University of Pisa, Italy
(2) Dipartimento di Scienze della Terra, University of Torino, Italy
(3) C.N.R. Istituto di Geoscienze e Georisorse, U.O.S. Pavia, Italy
(4) C.G.T., Università di Siena, San Giovanni Valdarno, Arezzo, Italy
The occurrence of metamorphic units with different
metamorphic imprints in the metamorphic core of the
Northern Apennines has been recognized since a long
time (Elter, 1975; Carmignani et al., 1978; Franceschelli
et al., 1986; Kligfield et al., 1986). However, the timing
of peak metamorphism is debated as few data are available (Kligfield et al., 1986).
Structural analysis performed on the Massa Unit on the
western side of the Apuane Alps (Northern Appennines)
revealed that the prominent fabric is an S2 penetrative
foliation transposing an earlier S1 foliation. L2 stretching lineation trends SW-NE and kinematic indicators
point to a top-to-the NE sense of shear. S2 foliation
affected most of the metamorphic porphyroblasts (e.g.
chloritoid, kyanite) developed during and after the metamorphic peak. D1 deformation phase, related to the
thickening stage of the belt, has been transposed by D2
so that D1 relics are observed only in D2 microlithons.
The nappe pile has been later affected by large scale
folds nearly parallel and perpendicular to the belt and
extensional tectonics at upper structural levels (Carosi
et al., 2002, 2004).
We conducted for the first time U-(Th)-Pb in-situ analysis on metamorphic monazites along both S1 and S2 foliations. Monazite on S2 gave concordant ages at ~ 1816 Ma Ma. Older ages (~ 20-24 Ma) have been obtained
for monazite along S1, within the S2 microlithons,
grown during prograde metamorphism. The latter ages
shift the metamorphic peak of several Myr with respect
to the ~ 27 Ma age proposed by Kligfield et al. (1986)
by K/Ar on white micas in the Apuane Unit. The latter
age is in conflict with the age of the youngest sediments
of the AU (Pesudomacigno) undergoing metamorphism
and deformation. These conflicting data led some Authors to shift the metamorphic peak towards even
younger ages (11-12 Ma, Patacca et al., 2013). This age
is unlikely because at 13-10 Ma AU has already reached
upper structural levels (< 9 km) after metamorphic peak
as suggested by zircon fission tracks (Balestrieri et al.,
2011 with references), being the annealing temperature
of zircons (~ 250°C) much lower with respect to the
peak metamorphic temperature (T ~ 400-500°C, Franceschelli & Memmi, 1999, Molli et al., 2000). Anyway
we must be aware that the different metamorphic units
in the metamorphic core could have registered (different) peak metamorphism in different times.
The new data allow to better constrain the timing of
superposition of the different tectonic units of the metamorphic core of the Northern Apennines. The occurrence of clasts from the MU with two foliations in the
cataclasites (“brecce poligeniche”) at the contact between MU and the overlying Tuscan Nappe (Carosi et
al., 2002, 2004) implies that tectonic coupling happened
after ~ 18-16 Ma.
Structural data suggest that the tectonic coupling between MU and Apuane Unit is achieved post D1 after the metamorphic peak and by a reverse shear zone
during contractional tectonics during the thickening
stage of the Northern Appennines. Extensional tectonics
occurred later, possibly at 13-10 Ma by the so called
“collapse folds” and low-angle and high-angle normal
faults at higher structural levels (depth < 9 km; Fellin
et al., 2007) when the metamorphic units have been already exhumed reaching the upper part of the crust and
deforming under brittle conditions (Carosi et al., 2002,
2004, Balestrieri et al., 2011).
REFERENCES
- Balestrieri, M. L., Pandeli, E., Bigazzi, G., R. Carosi, R.,
Montomoli, C., 2011. Age and temperature constraints
on metamorphism and exhumation of the syn-orogenic
metamorphic complexes of Northern Apennines, Italy.
Tectonophysics 509, 254–271.
39
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
- Carmignani, L., Giglia, G., Kligfield, R., 1978. Structural evolution of the Apuan Alps: an example of continental margin deformation in the Northern Apennines,
Italy. Journal Geology 8, 487–504.
- Carosi, R., Montomoli, C., Bertuccelli, N., Profeti, M., 2002. The structural evolution of the southern
Apuan Alps: new constraints on the tectonic evolution
of the Northern Apennines (Italy). Comptes Rendus
Geosciences 334, 339–346.
- Carosi, R., Montomoli, C., Pertusati, P.C., 2004. Late
tectonic evolution of the Northern Apennines: the role
of contractional tectonics in the exhumation of the
Tuscan units. Geodinamica Acta 17, 253–273
- Elter P. (1975) Introduction à la géologie de l’Apennin
Septentrional. Bull. Soc. Geol. France, 17: 956-962.
- Fellin, M.G., Reiners, P.W., Brandon, M.T.,
Wüthrich, E., Balestrieri, M.L., Molli, G., 2007.Thermochronologic evidence for the exhumational history of the Alpi Apuane metamorphic core complex,
northern Apennines, Italy. Tectonics 26, TC6015.
doi:10.1029/2006TC002085.
- Franceschelli, M., Leoni, L., Memmi, I., Puxeddu, M.,
1986. Regional destribution of Al-silicates and metamorphic zonation in the low-grade Verrucano metasediments from the Northern Apennines, Italy. Journal of
Metamorphic Geology, 4, 309–321.
- Franceschelli M, Memmi I. 1999. Zoning of chloritoid
from kyanite-facies metapsammites, Alpi Apuane, Italy.
Mineralogical Magazine 63, 105-110.
- Kligfield, R., Hunziker, J., Dallmeyer, R.D., Schamel,
S., 1986. Dating of deformation phases using K–Ar and
40Ar/39Ar techniques: results from the Norhern Apennines. Journal of Structural Geology 8 (7), 781–798.
- Molli, G., Giorgetti, G., Meccheri, M., 2000. Structural and petrological constraints on the tectono-metamorphic evolution of the Massa Unit (Alpi Apuane, NW
Tuscany, Italy). Geological Journal 35, 251–264.
- Patacca, E., Scandone, P., Conti, P., Mancini, S.,
Massa, G., 2013. Ligurian-derived olistostrome in the
Pseudomacigno Formation of the Stazzema Zone (Alpi
Apuane, Italy). Geological implications at regional
scale. Italian Journal of Geosciences 132, 463-476.
40
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Out of sequence thrust in the inner zone of northern Apennines:
insight from Elba Island nappe stack
Musumeci G.(1), Massa G.(2), Pieruccioni D.(2, 3), Mazzarini F.(4)
(1) Dipartimento di Scienze della Terra, Università di Pisa, Italy
(2) CGT, Centro di GeoTecnologie, Università di Siena, San Giovanni Valdarno, Arezzo, Italy
(3) Dipartimento di Scienze Chimiche e Geologiche, Università di Cagliari, Italy
(4) Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa, Italy
In the northern Tyrrhenian Sea, the Elba Island is one of
the westernmost portions of the northern Inner Apennine
belt and represents a key area to deciphering the structural evolution of the belt inner zone. The central-eastern Elba Island is made up by nappe stacking of several
sedimentary and metamorphic tectonic units, derived
from both continental and oceanic domains (Trevisan,
1950; Bortolotti et al., 2001). Since the Late Miocene,
nappe stack was affected by emplacement of magmatic
rocks rocks (M. Capanne and Porto Azzurro plutons ~
6.8-5.9 Ma), followed by postcollisional extension, with
development of a low angle normal fault (i.e. Zuccale
fault; Keller and Pialli, 1990; Pertusati et al., 1993).
A noteworthy feature of Elba island nappe stack is a
anomalous tectonic repetition of Tuscan and Ligurian
units thrust sheets due to a slice of Tuscan nappe sequence (Complex III) tectonically sandwiched between
two thrust sheets of Ligurian units. The Complex III
is made up of the Rio Marina Unit (Deschamps et al.,
1983) and the tectonically reduced Tuscan Nappe sequence. The former consists of Rio Marina Fm. (Late
Paleozoic metasandstones and phyllites) and Verrucano
Fm. (Middle Trias metasandstone). The overlying Tuscan nappe sequence is made up of Mesozoic carbonate
formations, tectonically overlain by Scaglia Fm. which
at the map scale discordantly rests above the Jurassic
carbonate formations, and Rio Marina Fm. phyllites.
This structural setting is consistent with the ‘Serie ridotta”, interpreted as the result of Middle Miocene extension of the chain (Carmignani et al. 2004).
The nappe stack is folded in a NW-SE striking kilometre-scale antiformal tight fold continuously exposed
along the eastern Elba coastline from Ortano to the
north of Rio Marina. The antiform is characterized by a
gently (5° - 30°) N-NW plunging axis and an eastward
vergence with a shallowly westward dipping axial plane
surface, which refolded the previous foliation (S1) and
bedding (S0). The axial plane cleavage is well developed
in phyllites and metasandstones and locally appears as a
penetrative main foliation at mesoscale (S2), wrapping
lenses of massive quartz - conglomerates (“Anagenites”
Auct.). Locally S-C structures show an eastward sense
of shear. The antiform hinge zone and the normal limb
are well exposed along the coastline to the north of Rio
Marina. Phyllites and metasandstones of the Rio Marina Fm show vertical lying bedding (S0) and subparallel
cleavage (S1). Locally (Vigneria beach) decametric isoclinal folds, associated with S1, are recognized. Southward Rio Marina the antiform inverted thinned limb is
cross cut by a tectonic contact. The serpentinites slice at
the top of the Acquadolce Unit appear under this tectonic contact. Field evidences and borehole data show that
the antiform is in turn cross-cut by the Zuccale Fault.
Then, by high angle normal and strike-slip faults characterized by Fe-hydroxides veins.
The eastward vergent antiform, exposed along the eastern coast, refolded the early nappe stack leading to the
unusual tectonic interfingering of the Tuscan and Ligurian Units. Thus the lower serpentinite slice, cropping out
below the Tuscan derived metamorphic and sedimentary units of Complex III, corresponds to the laminated
inverted limb of antiform, successively affected by the
contact metamorphism related to Porto Azzuro pluton
emplacement.
Age of post nappe folding deformation is bracketed between the age of the folded “Serie Ridotta” (Late Langhian, 13 Ma) and the emplacement of intrusive rocks
dated in the central-eastern Elba as being from the Messinian (7-6 Ma).
Therefore, the anomalous tectonic repetition of Tuscan
and Ligurian units thrust sheets in the eastern Elba nappe
stack gives evidence of Middle-Late Miocene out-of-sequence thrusting postdating nappe stack and predating
granite emplacement and upper crustal extension (Late
Miocene-Pliocene). We suggest that collisional tectonics
in the inner zone of northern Apennines was polyphased
41
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
with early stacking of tectonic units followed by out of
sequence thrust predating the eastward shifting of the
thrust front towards the external zone during late Miocene-Pliocene.
REFERENCES
- Bortolotti, V., Fazzuoli, M., Pandeli, E., Principi, G.,
Babbini, A., & Corti S. (2001). Geology of Central and
Eastern Elba Island, Italy. Ofioliti, 26 (2a), 97 – 150.
- Carmignani, L., Conti, P., Cornamusini, G. & Meccheri, M. (2004). The Internal Northern Apennines, the
Northern Tyrrehenian sea and the Sardinia – Corsica
block. Special Volume of the Geological Society for the
IGC 32 Florence-2004, 59-77.
- Deschamps, Y., Dagallier, G., Macaudière, J., Marignac, C., Moine B. & Saupé, F. (1983). Le gisment de
pyrite-hématite de valle Giove (Rio Marina, Ile d’Elbe,
Italie), Partie 1. Schweiz. Mineral. Petrogr. Mitt. 63,
149-165.
- Keller, J.V.A. & Pialli G. (1990). Tectonics of the island
of Elba: a reappraisal. Boll. Soc. Geol. It., 109, 413-425.
- Pertusati, P.C., Raggi, G., Ricci, C.A., Duranti, S.
& Palmeri, R. (1993). Evoluzione post-collisionale
dell’Elba centro-orientale. Mem. Soc. Geol. It., 49,
297-312.
- Trevisan, L. (1950). L’Elba orientale e la sua tettonica di scivolamento per gravità. Mem. Ist. Geol. Univ.
Padova, 16, 5-39.
42
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Paleogeographic problems of the Eocene foreland basin
of the south-central Pyrenees
Emiliano Mutti
University of Parma, Italy
In the Eocene foreland basin of the south-central Pyrenees thick and extensive accumulations of basinal
turbidites, the Hecho Group turbidites, have long been
considered as sourced from the east, i.e. from the thick
alluvial, fluvio-deltaic and shelfal strata outcropping
in the Tremp-Graus syncline, through feeder channels
crossing the lateral ramp of the Cotiella thrust sheet.
For this reason and because of the very good exposures,
this basin and its turbidites have become very popular
worldwide.
Field work I carried out with my co-workers over the
last 25 years (after 20 years spent studying the Hecho
Group turbidites) shows that (1) the Tremp-Graus basin is entirely preserved and does not contain channels
funneling sediment to the west; (2) paleocurrent directions, stratigraphic relationships and facies distribution
patterns clearly indicates that the Tremp-Graus basin, a
piggyback basin on top of the Tremp Unit, was separated since the Castissent time (early Eocene) from the
turbidite Hecho Group basin by a structurally-controlled
ridge, herein termed the Foradada Ridge. The ridge was
the expression of the oblique transpressive belt associated with the southward and westward translation of the
Tremp Unit. The Foradada Fault is the most prominent
feature of the ridge separating two basically different
domains. Along this fault, the northern and southern
margins of the basin came into contact through time as
a result of the dextral slip motion of the fault. The main
right-lateral motion occurred during the late-middle Eocene. The northern margin, i.e. the Tremp-Graus basin,
displays spectacular northerly-derived deltas and fandeltas (Castissent and Santa Liestra time); at the same
time, the southern margin shows a large southerly-fed
river delta system (La Fueva delta system). The mudstone-dominated delta-slope facies of this delta interfinger with the Hecho Group turbidites. The source of
these turbidites is thus represented by southerly-fed delta systems that migrated westward as a result of thrust
propagation. Much of the La Fueva delta system must
now be buried below the Montec and the Sierra Marginales thrust sheets.
The location of the main source area of the Hecho Group
turbidites raises several problems. The large volume
of these turbidites and the lateral continuity of many
sandstone beds favour a source from relatively large
and mature fluvio-deltaic systems with drainage basins
probably located in the Iberian and Catalan chains. A
similar paleogeographic setting is that of the sandy flysches of the northern Apennines that had an extra-orogenic source area being mainly fed from the Alps.
The lesson that can be learnt from the south-central Pyrenean basin is that a reasonable paleogeographic understanding of the fill of a tectonically-active basin can
only be achieved through an approach that includes sedimentologic, stratigraphic, and structural studies at local
and regional scale.
43
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Microstructural evidence of weakening mechanisms developed along
incipient Low-Angle Normal Faults in pelagic limestones
(Southern Apennine, Italy)
Novellino R.(1), Prosser G.(2), Viti C.(1), Spiess R.(3), Agosta F.(2), Tavarnelli E.(1), Bucci F.(4)
(1) Dipartimento di Scienze Fisiche, della Terra e Ambientali, Università degli Studi di Siena, Italy
(2) Dipartimento di Scienze Geologiche, Università della Basilicata, Potenza, Italy
(3) Dipartimento di Geoscienze, Università degli studi di Padova, Italy
(4) CNR-IRPI, Perugia, Italy
Low-Angle Normal Faults (LANFs) consist of shallowly-dipping extensional tectonic structures, whose origin
relates to a mechanical paradox currently debated by a
number of researches. The easy slip along these faults
suggests a strain-weakening process active during fault
nucleation and growth. Weakening mechanisms may include: i) presence of weak minerals; ii) high fluid pressure which, causing a drastic reduction of the effective
stress, and iii) dynamic fault weakening during coseismic rupture.
In the Basilicata portion of Southern Apennines, LANFs
have been extensively studied by geological mapping
and field structural analysis. Differently, a detailed microstructural observations are not hitherto available in
the geological literature. For this reason, in this note, we
summarize the results of microstructural analysis carried out on fault rock samples collected from a well-exposed mesoscopic LANFs. The present work is aimed
at analyzing the weakening mechanisms that took place
along the study faults.
The incipient study LANFs are characterized by a narrow and discontinuous damage zone surrounding a very
thin fault core that include a discrete slip-surface. The
offset is in the range of tens of centimeters to few meters. At the microscope scale, the sampled rocks reveal
the coexistence of different structural features such as:
i) pervasive shape preferred orientation defined by elongated grains of calcite, producing a distinct foliation;
ii) Crush Microbreccia (CM), formed of angular clasts
locally in contact with each other; iii) several Ultracataclastic Veins (UV), departing from the slip-surfaces
and cutting across the slip-zone. TEM investigation
reveal the presence of ultrafine to calcite-nanoparticles
(<200 nm) aggregate within UV, and iv) decarbonation features, where calcite grains exhibit irregular
boundaries, vacuum and vesicles, most likely related
to degassing processes. Thermal decomposition results
in formation of a calcite aggregate made of lenticular
calcite grains, 1 to 10 micron long. This honeycomb
like structure of calcite grains shows well-defined
shape- (SPO) and crystallographic-preferred orientations (CPO), consistent with the shear sense.
These latter microstructural features, testify that in
localized area, next to the slip-surface, an abrupt increase of temperature was accompanied by dynamic
recrystallization.
At least, two generation of calcite veins, approximately orthogonal to the slip-surface, show systematic
cross-cutting relationships with the above illustrated
structural features.
Overall, the investigated features form a complex
structural network resulting from ductile to brittle deformation mechanisms, and microstructural analysis
provides significant insight in the static and dynamic
fault weakening mechanisms acting along the shear
zone.
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state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
The role of strike-slip tectonics in the early to late formation of the
southern Calabrian Alpine-Apennine chain system
(Calabria, Southern Italy)
Gaetano Ortolano(1), Vincenzo Tripodi(2), Rosolino Cirrincione(1), Salvatore Critelli(2), Francesco Muto(2),
Roberto Visalli(1)
1 Dipartimento di Scienze Biologiche Geologiche ed Ambientali, Università di Catania, Italy
2 Dipartimento di Biologia, Ecologia e Scienze della Terra, Università della Calabria, Italy
The kinematic and the rheological features of some earlyto late-Alpine strike-slip tectonic structures have been here
investigated with the aim to contribute to better constrain
the former as well as the recent stages of the arc shaped
formation of the southern Calabrian orogenic segment.
The development of these strike-slip tectonics have been
always widely invoked by several authors to explain the
drift of the Calabrian terrane as a consequence and/or as a
precursor of the Alpine back-arc basin expansion. Nevertheless, clear evidences of these deep seated junction bands
are resulted rarely recognizable due to the pervasive activity of the Oligo-Miocene thin skinned thrusting accompanied by Plio-Pleistocene normal tectonics.
In this tectonic framework, the Calabrian orogenic segment can be interpreted as the result of the amalgamation
of remnants of an original segment of the southern European Hercynian chain (Fig.1a) reworked during the Alpine-Apennine orogeny (Fig.1b). This evolution led to the
formation of a composite terrane (i.e. Calabride Composite Terrane - CCT) (Fig.1a) constituted by basement rocks
presently merged in several Hercynian or possibly older
sub-terranes. These rocks were locally overprinted during
the different stages of the Alpine metamorphic cycle,
which also affected part of the Mesozoic oceanic-derived
units and sedimentary sequences, and were definitively
stacked during the Alpine-Apennine thin skinned thrusting event. In this geodynamic scenario, results clear as the
reconstruction of the evolution of the strike-slip tectonics
from its embryonic (Late Cretaceous-Early Paleocene) to
the present-day activity plays a crucial role in the not yet
fully unraveled distribution of plate and/or microplate that
crowd the geodynamic puzzle of the western Mediterranean realm.
In this framework, in order to constrain the evolution of
the strike-slip tectonics of the southern CCT, three different
strike-slip shear zones, aligned along the junction between
the Aspromonte and Serre Massifs, have been structurally
investigated, contributing also to explain the lateral jux-
taposition of differently evolved crystalline basement domains.
The first one, the Palmi Shear Zone (PSZ) represents the
most ancient relic of transcurrent activity recorded in this
sector of the southern Alpine chain. It is characterized by
a 400 m wide tabular structure with subvertical foliation,
involving skarn, migmatite and tonalite belonging to an
original southern European Hercynian high grade crustal
section. The present-day average attitude is WNW-ESE,
and can be followed in outcrop for about 1200 m inland up
to disappear below a Tortoanian age silicic-clastic formation (Ortolano et al., 2013). Field evidences accompanied
by Rb-Sr age data on whole mica (Prosser et al., 2003),
brackets the mylonitic shearing activity between 56 to 51
Ma. Structural analysis of mylonitic rocks (Fig. 1c’,c’’)
highlighted as the average attitude of the subvertical foliation as well as the stretching lineation ranging from W-E,
to NW-SE with a transport direction top-to-E, SE in the
present-day geographic coordinates (Ortolano et al., 2013)
(Fig.1c’).
The second and the third ones, the Nicotera-Gioiosa Shear
Zone (NGSZ) and the Molochio-Antonimina Shear Zone
(MASZ), respectively, represent the most prominent morphological evidences of the NW–SE fault system in the
southern CCT.
The (MASZ) bordering the southern end of the Gerace–
Antonimina graben, and can be considered as the natural
brittle evolution of the deepest-rooted Palmi Shear Zone
(PSZ), outcropping in the southern portion of the Gioia
Tauro basin (Fig.1b, d).
The NGFZ is a relevant regional structure of the strike–slip
fault system that borders the Strait of Siderno to the north.
In oblique-slip fault systems, displacement generates important topographic gradients with associated uplift and
subsidence.
The activity of these two last shearing zones can be
framed from the Serravallian–Tortonian stages up to now.
The present-day average attitude is WNW-ESE and in
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Figure 1 a) Geological sketch map of Alpine and pre-Alpine chains in the Western Mediterranean area; b) Calabrian Peloritani Orogen schematic map (after Angì et al. 2010) with study areas location; c) Evidences of mylonitic related structures of the
Palmi shear zone: c’) sheat-fold in mylonitic leucogneiss with E-W vertical attitude, c’’) altered feldspar porphyroclast within
mylonitic skarns; d) Overview of the Molochio-Antonimina tectonic aligment.
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their evolution have exhibited both strike–slip and normal
kinematics (Tripodi et al., 2013).
From this brief review, results clear as the present-day
tectonic framework of southern CCT scenario, cannot be
explained invoking just the main juxtaposition of a northern (central and northern Calabria) and a southern sector
(southern Calabria and north-eastern Sicily) approximately separated in correspondence of the Catanzaro trough
(Fig.1b). This subdivision has to be indeed completed
by other minor ones, based on one hand by evidences of
transcurent tectonic alignment testified by formerly developed mylonitic deep-seated shearing activity (i.e. PSZ), replaced by a well testified Tortonian age strike-slip tectonics
(MASZ and NGSZ) actually operating within an overall
extensional geodynamics as also supported by the structural data and for the contribution of the Miocene–Quaternary
tectono-stratigraphic history of the Siderno basin.
In this view, the protracted strike-slip tectonic activity passing from deep seated mylonitic shearing to brittle ones has
likely played a crucial role in the approaching the different
crustal sectors forming the actual southern CCT, by means
of the activation or re-activation of transcurrent crustal-scale shear zones, representing lithospheric structures
that act as highly localized deformative weakening bands
that facilitated the movement between more rigid crustal
blocks.
REFERENCES:
- Angì G. Cirrincione R. Fazio E. Fiannacca P. Ortolano G. & Pezzino A. (2010). Metamorphic evolution of preserved Hercynian crustal section in the
Serre Massif (Calabria-Peloritani Orogen, southern
Italy). Lithos 115:237–262.
- Cirrincione R. De Vuono E. Fazio E. Fiannacca P.
Ortolano G.Pezzino A. & Punturo R. (2010). The
composite framework of the southern sector of the
Calabria Peloritani Orogen. Rendiconti Online Societa Geologica Italiana 11, 1, 93-94.
- Ortolano, G., Cirrincione, R., Pezzino, A., Puliatti, G. (2013). Geo-Petro-Structural study of the
Palmi shear zone: Kinematic and rheological implications Rendiconti Online Societa Geologica
Italiana, 29, pp. 126-129.
- Prosser G. Caggianelli A. Rottura A. & Del Moro
A. (2003). Strain localization driven by marble layers: the Palmi shear zone (Calabria-Peloritani terrane, Southern Italy). GeoActa, vol. 2, pp. 155-166.
- Tripodi V. , Muto F. & Critelli S.(2013). Structural style and tectono-stratigraphic evolution of the
Neogene–Quaternary Siderno Basin, southern Calabrian Arc, Italy, International Geology Review,
55:4,468-481.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Relationships between the Kirşehir massif and the Sakarya zone (Turkey):
geological and petrographical data from the
Ankara-Erzincan suture and surroundings
Pandeli E.(1, 2), Elter F.M.(3), Toksoy Köksal F.(4), Principi G.(1)
(1) Department of Earth Sciences, University of Florence, Italy
(2) CNR-Institute of Geosciences and Georesources, Section of Florence, Italy
(3) DISTAV, University of Genoa, Italy
(4) Geological Engineering Department, Middle East Technical University of Ankara, Turkey
Anatolia Peninsula is a key area to reconstruct a coherent geodynamic model for the Eastern Mediterranean.
In particular, the geological framework of Eastern Mediterranean is the result of a series of geodynamic events
which, following the closure of Paleotethys in late Paleozoic (Cimmerian orogeny), led to ?Permian-Triassic rifting and ocean spreading in the equatorial part of
Pangea generating the Neotethys. The resulting ocean,
the Neotethys, was subdivided in various branches, separating a series of continental blocks between Gondwana and Laurasia. The Anatolian Peninsula (i.e. Anatolian
Plate) is geologically subdivided in three main zones,
from N to S, Pontides, Anatolides and Taurides. They are
divided by two main spectacular ophiolitic sutures: the
Izmir-Ankara-Erzincan suture zone (IAESZ), between
the Pontides (Sakarya Zone p.p.) and the Anatolides, due
to the subduction of the northern Neotethys branch; the
Southern Taurides suture (TSZ) due to the subduction of
the southern Neotethys branch.
Our study was performed in the areas to the north-east
of Ankara (W-SW of Çankırı, i.e. Kalecik and Şabanözü,
NW and SW of Çorum and SE of Amasya), where the
Sakarya Zone units crop out in the surroundings the
IAESZ, where the oceanic Ankara Ophiolitic Melange
(Sakarya Zone ) is in tectonic contact with the continental Anatolian Units (Kırşehir Massif). In the above
said localities, we studied the relationships between the
continental successions of the Sakarya Zone and the
Ophiolitic Melange. In particular, geological and structural surveys were made in typical sites and samples of
rocks were collected for petrographic and microstructural analyses. The aim of the study is to define the lithological-stratigraphical features of the successions, their
compositional features and structural evolution both of
the Ankara Ophiolitic Melange and of the more or less
metamorphic continental successions of the Sakarya
Zone in the above said areas.
The Ankara Ophiolitic Melange is made up of Mesozoic
brecciated ophiolitic rocks; in particular it is mostly a
serpentinite breccia including olistoliths of serpentinite,
gabbro, basalt, chert and pelagic limestone in a serpentinite-shaly foliated matrix. Locally olistoliths of
Mesozoic platform carbonates (likely coming from the
Kırşehir succession) are also present. The size of the
olistoliths varies from centimetric to hectometric; in this
latter case, portions of the pristine stratigraphic succession (e.g. stratified pelagic limestones, pillow basalts
with cherts at the top) are preserved. Generally the biggest ophiolitic bodies are at the top of the melange and
their contact is locally underlined through shear zones
that are also present at different levels of the melange.
The structural data collected in the different sites show
that the shear zones are characterized by a prevalent topto-the NE sense of shear.
The continental units of the Sakarya Zone succession
are made up of prevalent high diagenetic to low-grade
metamorphic rocks, Paleozoic-Triassic in age and Mesozoic to Tertiary mostly carbonate formations. In the
Çankırı area, the former are represented by metasiliciclastics (phyllite and metasandstone with rare carbonate
interbeds), locally intruded by intermediate-basic magmatic dykes, passing vertically to stratified to massive
carbonate succession with horizons of pillow basalts. In
Çorum area, the metasiliciclastic rocks overlie middle
grade regional polymetamorphic rocks (garnet-bearing
micaschist and gneiss s.l., marble and amphibolites),
locally characterized by a blueschist facies event. Instead, vario-coloured phyllites and green metavolcanites prevail in the Amasya area below the Mesozoic
carbonate successions. These successions are generally deformed by three events: 1) D1 that produced a
fine-grained continuous foliation (quartz+sericite+chlorite+calcite+oxides+organic matter±albite) with mineral lineations locally associated to isoclinal/tight folds;
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2) D2 folding which is characterized by spaced zonal
to discrete crenulation cleavage (generally underlined
by alignment of oxides+organic matter ± sericite) and
by mostly NE-SW striking axes (except the areas west
and south-west of Çankırı, where SE dipping axes are
generally present); 3) local D3 weak folding without
blastesis that is defined by kinks with NW-SE striking
axes.
In the Çorum micaschist, gneiss and amphibolites, the
blue amphibole appears nematoblastic to diablastic re-
spect to the main (D1? or pre-D1?) schistosity and
is retrogressed into Greenschist Facies mineral assemblages.
The Ophiolitic Melange tectonically underlies the the
Sakarya Zone continental successions, but locally (e.g.
along the road Çorum-Alaca) their geometrical relationships are reversed. This can be due to the activity
of main transcurrent structures that also produced the
variation of the axial strike of the D2 folds within the
Sakarya continental units in the different areas.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Seep carbonates and chemosynthetic coral communities in the Bocco
Shale (Internal Ligurides, Northern Apennine, Italy) as record of trenchslope limit in the Early Paleocene alpine accretionary wedge
Luca Pandolfi (1,2), Chiara Boschi (2), Edoardo Luvisi (1), Alessandro Ellero (2), Michele Marroni (1, 2),
Francesca Meneghini (1)
(1) Dipartimento di Scienze della Terra, Università di Pisa, Italy
(2) Istituto di Geoscienze e Georisorse, CNR, Pisa, Italy
In Northern Apennines, the Internal Liguride units are
characterized by an ophiolite sequence that represents
the stratigraphic base of a Late Jurassic-Early Paleocene sedimentary cover. The Bocco Shale represents the
youngest deposit recognized in the sedimentary cover
of the ophiolite sequence, sedimented just before the inception of subduction-related deformation history.
The Bocco Shale has been interpreted as a fossil example of deposits related to the frontal tectonic erosion of
the alpine accretionary wedge slope. The frontal tectonic erosion resulted in a large removal of material
from the accretionary wedge front reworked as debris
flows and slide deposits sedimented on the lower plate
above the trench deposits. These trench-slope deposits
may have been successively deformed and metamorphosed during the following accretion processes.
The frontal tectonic erosion can be envisaged as a
common process during the convergence-related evolution of the Ligure-Piemontese oceanic basin in the
Late Cretaceous-Early Tertiary time span.
In the uppermost Internal Liguride tectonic unit (Portello Unit of Pandolfi and Marroni. 1997), that crops-out
in Trebbia Valley, several isolated blocks of authigenic
carbonates, unidentificated corals and intrabasinal carbonatic arenites have been recognized inside the finegrained sediments that dominate the Early Paleocene
Lavagnola Fm. (cfr. Bocco Shale Auctt.).
The preliminary data on stable isotopes from blocks of
authigenic carbonates (up to 1 m thick and 3 m across)
and associated corals archive a methane signatures
in their depleted carbon isotope pattern (up to δ13C
–30‰ PDB) and suggest the presence of chemosynthetic paleocommunities.
The seep-carbonates recognized at the top of Internal
Liguride succession (cfr. Bocco Shale Auctt.) occur
predominantly as blocks in very thick mudstone-dominated deposits and probably developed in an environment dominated by the expulsion of large volume of
cold methane-bearing fluids focused in the frontal part
of the Early Paleocene alpine accretionary wedge.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
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Explosion breccias
Peacock D.C.P.
Statoil, Bergen, Norway
Breccias with clear cements occur in carbonate rocks
in transpressional thrust sheets in Wyoming (USA)
and elsewhere. They are not cataclasites because they
have not been created by friction along faults, but appear to have been produced by explosion of the host
rocks, so are here defined as explosion breccias. CO2
is generated by metamorphism of carbonates or by
hydrocarbon maturation. The CO2 migrates up the
thrust sheet because it is less dense than water, and
is trapped in the hanging-wall anticline. The top seal
is breached, either by the large column of CO2 or by
strike-slip faulting. This causes rapid decompression
of pore fluids, with more CO2 coming out of solution as pressure and temperature drop, with explosive
brecciation caused as escaping CO2 elevates pore
pressure as it migrates upwards. This is analogous to
the role of degassing in explosive volcanic eruptions.
The loss of pore pressure and decrease in acidity as
the CO2 escapes causes cementation of the brecciated rock.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Stresses, overpressure and transient strike-slip during tectonic inversion
Peacock D.C.P. (1), Casini G. (1), Anderson M.W. (2), Tavarnelli E. (3)
(1) Statoil, Bergen, Norway
(2) School of Earth, Ocean and Environmental Sciences, University of Plymouth, UK
(3) Dipartimento di Scienze della Terra, Università di Siena, Italy
Changes in the orientations and relative magnitudes of
stresses during the tectonic cycle will cause a transient
phase in which the intermediate compressive stress is
vertical, tending to promote strike-slip faulting. This can
occur between regional extensional (maximum compressive stress vertical) and regional contractional (minimum compressive stress vertical), either at the start
of basin inversion or after the main phase of orogenic
contraction. Such variations in the relative magnitudes
of the stress axes can be promoted by variations in overburden or by variations in tectonic forces. The reduction
of overburden during uplift and erosion can cause overpressure to develop in units with a top seal, manifested
by vertical or horizontal veins, strike-slip faults, thrusts
and inverted normal faults. The development of such
uplift-induced overpressure may explain the localisation of deformation during basin inversion, such as the
patchy occurrence of Alpine inversion in parts of southern England. It is also possible that transient phases of
strike-slip faulting during inversion events may breach
seal units, thereby promoting hydrocarbon migration
and reducing fluid pressure.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
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The Epiligurian basin in the middle Enza valley (Northern Apennines, Italy):
evidences of a Priabonian-Serravallian syn-depositional
polyphased deformation zone
Alberto Piazza(1), Andrea Artoni(1)
(1) Università degli Studi di Parma, Dipartimento di Fisica e Scienze della Terra “Macedonio Melloni”,
Parma, Italy
The Epiligurian succession cropping out in the
middle Enza Valley belongs to one of the widest
Eocene-Miocene wedge-top basin of Northern
Apennines of Italy (Fig. 1a). New stratigraphic and
structural data, collected through a detailed geological survey (Fig. 1b) and integrated with literature data, allow a tectono-sedimentary evolutionary
model to be proposed. The model highlights that
the sedimentation is controlled by the activity of
a diffused and polyphased deformation zone since
Priabonian to Serravallian. This zone, here named
Enza Valley Deformation Zone (EVDZ), underwent
two main tectonic phases (Fig. 2): 1) a low angle
extensional phase (Priabonian – Early Rupelian),
2) a left lateral transpressive phase (Rupelian-Serravallian). Both tectonic phases are syn-sedimentary as evidenced by: unconformities, lateral variations in thicknesses of stratigraphic units and the
presence of chaotic deposits within the sedimentary
succession.
The first tectonic phase (Priabonian- Early Rupelian) is evidenced by the arenaceous-conglomeratic lithofacies of Val Pessola Member (Ranzano
Formation, Ran 2a) that fills a narrow, localized
and asymmetric basin whose depocenter is located
toward south in the study area. On the southern
margin of the basin (now overturned), the Ran2a
lithofacies unconformably overlays the lowermost
stratigraphic units of the Epiligurian succession
(Baiso clay breccias and Monte Piano formations
– Cerina Feroni et al., 2002) which, on their turn,
lays on the Cassio Unit. The latter is the uppermost tectonic unit of the Ligurian tectonic stack
which, from bottom to top, is given by Caio, Groppallo and Cassio units (Fig. 1b). Instead, toward
north-northwest, the Ran 2a onlaps on the Caio
tectonic units (the lowermost Ligurian unit) and
onto normal faulted blocks of Monte Piano-Ran 2a
succession. The above stratigraphic and structural
relationships suggest that the Ran 2a was deposit-
ed in a basin formed during the development of a
south–dipping, low angle extensional faults system
which exhumed the lowermost Ligurian tectonic
unit (Caio Unit) and created a narrow, localized
depocenter which is about 500 m deep to the south
(fig. 2, stages 1-3)
The second tectonic phase (Rupelian-Serravallian)
is characterized by transpressive tectonics. It is testified by the development of a complex structural
association of faults and folds that affect the Epiligurian succession up to the Contignaco Formation
(Burdigalian), the underlaying Ligurian units and
the earlier formed low angle extensional faults system. The overall geometry of the structure formed
during this second phase is an overturned syncline
having WNW-ESE axis and a NNE-SSW axial trace:
the Enza Valley syncline of Ottria et al. (2001). In
detail, it is a very complex structure, characterized
by two en-echelon, overturned polyphased synclines that are cross-cut by both transcurrent fault
systems, striking between N-S and NNE-SSW, and
low-angle embricate thrust systems (Fig. 1b). The
association of all these structures, their orientations
as well as the mesostructural data can be framed in
a SW-NE trending left lateral transpressive zone.
The syn-depositional and transpressive activity of
the EVDZ is evidenced by the occurrence of a depocenter located in the NW portion of the study area
and filled by the Lagrimone sandstone member
(Late Rupelian) (Cerrina Feroni et al., 2002). The
Lagrimone sandstone can be considered the marker
of the inception of the transpressive phase of the
EVDZ. The end of this phase can be defined by the
units sealing the EVDZ toward north where NNESSW trending structures (Enza, the Rio Maillo and
the Monte Faiedolo anticlines) are unconformably
buried under the Langhian-Serravallian deposits
of the Bismantova Group (De Nardo et al., 1991).
Thus, the EVDZ transpressive phase is developing
since Late Rupelian to Serravallian.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Figure 1 - Location (a) and structural map (b) of the studied area.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Figure 2 - Sketches illustrating the stratigraphic and tectonic evolution of the Epiligurian wedge-top basin from Priabonian
to Serravallian.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Looking at the EVDZ from a regional point of view,
it can be prosecuted toward both north and south.
Northward, as mentioned above, it is traceable into the
NNE-SSW trending structures which preserve a Miocene syn-depositional activity as already suggested by
De Nardo et al. (1991). Southward it can be associated to the Monte Ventasso structure developed during
lower-middle Miocene (Vescovi 2005). Therefore, the
EVDZ can be part of a wider and longer deformation
zone crossing obliquely the main NW-SE oriented compressive structures of the Northern Apennines. The results of this study give new insights on the geometries
and the behavior of Apenninic transversal structures and
reveal how these structures control the tectonic-sedimentary evolution of the Epiligurian wedge-top basins
since the inception of their formation during Eocene
and Oligocene.
REFERENCES
- Cerrina Feroni A., Ottria G., Vescovi P. (2002). Carta
Geologica d’Italia alla scala 1:50.000, Foglio 217 “Neviano degli Arduini”. Servizio Geologico d’Italia - Regione Emilia Romagna, S.E.L.C.A., Firenze.
- De Nardo M.T., Iaccarino S., Martelli L., Papani
G., Tellini C., Torelli L, Vernia L. (1991). Osservazioni sull’evoluzione del bacino satellite epiligure Vetto-Carpineti-Canossa (Appennino Settentrionale).
Mem. Descr. Carta Geol. d’It., XLVI 209-220, Roma.
- Ottria G., Catanzariti R., Cerrina Feroni A. (2001). The
Ranzano unit boundaries in the type area: Lower Oligocene events in the epi-Ligurian Succession (northern
Apennines,Italy). Eclogae geol. Helv., 94, 185-196.
- Vescovi P. (2005). The Middle Miocene Mt. Ventasso
Mt. Cimone arcuate structure of the Emilia Apennines.
Boll. Soc. Geol. It., 124, 53-67.
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Evolution of the Alps-Apennine boundary:
EU/IB/AD transcurrence leading to a crustal vortex
Gianfranco Principi(1), Benedetta Treves(2)
(1) Dipartimento di Scienze della Terra, Università di Firenze, Italy
(2) Istituto Geoscienze e Georisorse, CNR, Sezione di Firenze, Italy
The present junction between the Alpine and Apenninic
chains is an amazing crustal hinge, shaped like a vortex
(‘Ligurian Knot’, auctt.), that links two orogenic belts
with opposite polarity (Western Alps/Northern Apennines) and is cut through by a N-S transcurrent fault (Sestri-Voltaggio Line). This boundary got localized at the
junction of the European, Iberian and Adriatic plates,
along important inherited lithospheric discontinuities
that played a major tectonic role since at least Triassic
and certainly Jurassic and Cretaceous times. The kinematics of this junction represents a key point to unravel the geodynamics of the Western Mediterranean area,
and has been puzzling geologists for over 50 years, but
is still not understood and a matter of debate.
We review the structures that have been proposed in
the many tectonic reconstructions of the area, trying to
model the EU/IB/AD kinematics. We try to address in
particular the following unsolved points:
1) What kind of deformation happens at depth under
the junction of the two chains with opposite vergence?
What are the deep lithospheric structures that controlled
the crustal deformation and superficial structures?
2) How is the rotation of Adria about a pivot point located at its edge structurally realized? What are the faults
and geologic processes that accomplish what kinematically appear as EU/IB and EU/AD rotations?
3) Is there a major partitioning of strain and/or decoupling in the crust and lithosphere? Can the lithosphere
rotate around a vertical axis?
4) The Corsica “Faces Game”: those who look from the
West see it as Alpine, those who look from the East see
it as Apenninic…. it may be instead correct one who
looks at it from the South, and sees a major role of transcurrence. We discuss the differences and similitudes between the Corsica/Apennines and Ligurian Alps/Apennines boundaries.
We propose that the ‘Ligurian Vortex’ could be kinematically explained through a sequence of at least three
transcurrent stages active from Late Cretaceous up to
recent with different directions:
- The first one was active as a sinistral transpression
during the Late Cretaceous-Eocene along the SWNE original IB/AD transtensional plate boundary, that
also continued many older (Triassic and Jurassic) rift
structures still recognizable along the Iberian margin,
in Provence, in the Adriatic basement of the Northern
Apennines (La Spezia basin, isopic zones of the Tuscan sequence), in the Sudalpine margin (Belluno basin)
and in the Southern Apennines (Lagonegro basin). The
NE-SW trend is still recognizable along the Canavese
Line, the Pamplona Fault (dividing the Pyrenees from
the Cantabrian Chain) and the External massifs of the
Western Alps (Pelvoux, Aar) probably reflecting their
exhumation along this same SW-NE fault system. The
Sestri-Voltaggio Lineament also likely belonged to it,
but it subsequently (Oligocene to Pliocene) suffered a
60-70 degrees rotation along with the Corso-Sardinian
Block and Adriatic basement.
- The second movement occurred from Eocene on, along
a set of N-S left-lateral strike-slip faults that took the
northward displacement of Adria+Africa towards stable Europe and allowed a transform scissor/cut between
a portion of Adria subducting westwards under Iberia
(Apennines) and a portion of Adria overriding the European crust along the Alpine arc. The Late Eocene age of
calcalkaline magmatism in western Sardinia (38.3Ma),
and Provence (about 35Ma), related to the already ongoing Apenninic subduction was either contemporary or
even older than the blueschist metamorphism in Corsica, affecting also European margin units (comprising
Paleozoic granitoids), and together with the presence
of non metamorphic ophiolitic units above the “Alpine
Corsica” tectonic pile support the hypothesis that the
Corsican Schistes Lustrèes represent metamorphosed
fragments of the subducted Apenninic (Ligurian) ocean.
- The third kinematic stage, which includes the Late Tertiary anticlockwise rotations at the surface, could have
been accomplished at a lithospheric level through an
ENE-WSW directed transcurrent drag system that increased in displacement from north to south as a rota-
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tion of Adria around the ‘Ligurian hinge’. This probably
caused the strong curvature in the Western Alps, extension in the Tyrrhenian Sea and compression along the
Apenninic front.
We stress the need to recognize a major transform cut
within Adria, probably already present in the Cretaceous, but especially important during this stage, that
could allow this plate to split into two parts: one being
subducted along the Apennines and the other overriding
the European crust along the Alpine belt.
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Walking through the Tethys in the Monviso Ophiolite (Piemonte, Italy)
Franco Rolfo(1, 2), Gianni Balestro(1), Alessandro Borghi(1), Daniele Castelli(1, 2), Simona Ferrando(1), Chiara Groppo(1), Pietro Mosca(2), Roberto Compagnoni(1)
(1) Dipartimento di Scienze della Terra, Università di Torino, Italy
(2) CNR Istituto di Geoscienze e Georisorse, unità di Torino, Italy
The Monviso Ophiolite (MO) in the Italian Western
Alps is one of the best known relics of oceanic crust
in the orogen. Moreover, it is one of the strategic areas
chosen to represent the geodiversity of Piemonte Region
(Rolfo et al. 2014). The MO gives the chance to see and
appreciate different portions of the ancient ocean along a
relatively short mountain trail; from the Po river springs
at Pian del Re, a path from 2000 m up to about 2350 m
a.s.l. shows all different ophiolitic lithologies – modified after the Alpine evolution - within few kilometers.
GEOLOGICAL SETTING
The MO is a N-S trending body, 35 km long and up
to 8 km wide, tectonically emplaced between the un-
derlying continental-derived Dora-Maira Massif and the
ocean-derived Piemonte Zone metasedimentary units.
The MO formed during the Mesozoic opening of the
western Alpine Tethys and underwent eclogitic metamorphism during Alpine subduction (e.g. Lombardo et
al. 1978). The MO encompasses the whole lithological
spectrum of the Piemonte-Ligurian ophiolites: peridotite, gabbro, dolerite, basalt, as well as cover sediments
(Fig. 1).
The MO comprises two major tectonometamorphic
units, trending north-south and dipping to the west, separated by a major shear zone: the “Monviso Upper Unit”
to the west and the “Lago Superiore Lower Unit” to the
east (Castelli et al. 2014).
Figure 1 – Geological sketch map of the
Monviso area, with the excursion route
and location of Stops 1 to 8 described
in the text (modified from Castelli et al.
2014).
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Recent advances in petrology, geochemistry and geochronology suggest a short duration of igneous activity
in the MO and a short time span (from ca 170 to ca
150 Ma) for the entire Piemonte-Ligurian Tethys, with
an embryonic ocean (max 380 km wide; Piccardo et al.
2001) experiencing first oceanic hydrothermal alteration (Nadeau et al. 1993) and then, during the Alpine
subduction, eclogite-facies metamorphism (e.g. Lombardo et al. 1978). Later exhumation produced re-equilibration under progressively lower pressure conditions
at blueschist- and greenschist-facies.
A GEOLOGICAL TRAIL ACROSS THE TETHYS OCEAN
A general view of the MO internal structure is evident
from stop 1 between Pian Melzè and Pian del Re (Fig.
1), by looking southward to the ridge from Monte Grané
(2314 m) to Viso Mozzo (3019 m) and Monviso (3841
m). Along this section are exposed, from left to right
and from bottom to top: the serpentinite at Monte Grané
and in the lower ridge above Pian Melzè; the metagabbro at the foot of Viso Mozzo and the low ridge above
Pian del Re; the Viso Mozzo metabasite and the Colle
di Viso serpentinite, which crops out in the low ridge
between Viso Mozzo and Monviso.
Along the path from Pian del Re to Lago Fiorenza, the
first outcrop of serpentinite (Fig. 1, stop 2) deriving from
primary spinel-lherzolite of the upper mantle underlying
the oceanic crust, is either massive or sheared (Fig. 2a).
It mainly consists of antigorite ± clinopyroxene, brucite,
Mg-rich chlorite, Ti-clinohumite, metamorphic olivine
and chrysotile; ore minerals are magnetite, FeNi-alloys
and sulphides. Different generations of metamorphic
veins crosscut the serpentinite.
About 500 m SSE of Lago Fiorenza (Fig. 1, stop 3),
a folded elongated body of metasediments – originally covering the former oceanic crust – is tectonically
embedded within serpentinite. This sliver, about 50
m-thick, belongs to an eclogite-facies shear zone which
passes through Colletto Fiorenza. The metasediments
consist of impure marbles, calcschists and micaschists
grading to quartzite (Fig. 2b). Rare cm-thick layers of
metabasite are interbedded with metasediments.
At Colletto Fiorenza (Fig.1, stop 4), a tectonic contact
between calcschists and the overlying metagabbro (Fig.
2c) is marked by a zone from a few m to a few tens of m
thick of strongly sheared serpentinite and talc-carbon-
Figure 2 – (a) Stop 2: outcrop of serpentinite of the Basal Serpentinite Unit above Pian del Re; (b) Stop 3: folded calcschists
and impure marbles of the Basal Serpentinite Unit; (c) Stop 4: contact between serpentinite and metagabbro at Colletto Fiorenza; (d) Stop 5: smaragdite metagabbro at Lago Chiaretto; (e) Stop 8: eclogite-facies omphacite-bearing veins
cross-cutting the eclogitic FeTi-oxide metagabbro foliation.
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ate-amphibole-schist, with tectonic inclusions of banded eclogitic rocks.
Between Colletto Fiorenza and Lago Chiaretto (Fig.
1, stop 5), beautiful smaragdite metagabbro – former
Mg-Al-rich plutons in the lower oceanic crust - locally
includes transposed cm- to dm-thick dykes of metabasalts. The metagabbro shows a well developed foliation
and consists of a whitish matrix and emerald-green porphyroclasts of “smaragdite”, the local name for Cr-omphacite (Fig. 2d). The metabasaltic dykes, now eclogite,
are very fine-grained and locally preserve remnants of
a porphyritic structure. Few boulders preserve igneous
layering textures, with emerald-green bands (enriched
in Cr-omphacite) corresponding to layers with high
modal clinopyroxene.
West of the smaragdite metagabbro, along the path leading to Lago Lausetto and Rifugio Giacoletti, sheepback
rocks (Fig. 1, stop 6) consist of alternating layers of
eclogite and metagabbro from a few cm- to several dmthick. Eclogite largely prevails over metagabbro. The
melanocratic layers (now eclogite) derive from primary
FeTi-oxide gabbro, whereas leucocratic layers derive
from Mg-Al gabbro protoliths.
South of Lago Lausetto, along the path leading to Rifugio Giacoletti (Fig. 1, stop 7), a narrow alluvial plane
hides a shear zone separating Fe-Ti metagabbro mylonites (to the E) from foliated prasinite (to the W). No
primary features, such as pillow structure or porphyritic
texture, are preserved within the prasinite; nice pillows
can be observed in the nearby Vallone dei Duc. Prasinite is fine-grained and mainly composed of albite, clinozoisite/epidote, chlorite, amphibole, and accessory
rutile, titanite, apatite and opaque ores.
Finally, at the western side of Lago Superiore (Fig. 1,
stop 8), a layered eclogitic sequence contains small
(10x10 cm) lenses of low-strain domains still preserving the igneous microstructure and surrounded by large
volumes of eclogite-facies mylonites. Cigar-shaped
boudins of eclogite within the metagabbro outline a
complex interference pattern of folds. Eclogite-facies
veins are spectacular – and indeed very rare worldwide
- and witness fluid migration during subduction (Fig.
2e). They contain mostly Na-pyroxene and minor garnet, rutile and apatite. In tension gashes, most pyroxene
is fibrous.
REFERENCES
- Castelli, D., Compagnoni, R., Lombardo, B., Angiboust, S., Balestro, G., Ferrando, S., Groppo, C. &
Rolfo, F. (2014). The Monviso meta-ophiolite Complex:
HP meta-morphism of oceanic crust & interactions with
ultramafics. GFT – Geological Field Trips, in press.
ISSN: 2038-4947. 8-35.
- Lombardo, B., Nervo, R., Compagnoni, R., Messiga,
B., Kienast, J.R., Mevel, C., Fiora, L., Piccardo, G.B. &
Lanza, R. (1978). Osservazioni preliminari sulle ofioliti
metamorfiche del Monviso (Alpi Occidentali). Rendiconti della Società Italiana di Mineralogia e Petrologia,
34, 253-305.
- Nadeau, S., Philippot, P. & Pineau, F. (1993). Fluid
inclusion and mineral isotopic compositions (H-O-C) in
eclogitic rocks as tracers of local fluid migration during
high-pressure metamorphism. Earth and Planetary Sciences Letters, 114, 431-448.
- Piccardo, G.B., Rampone, E., Romairone, A., Scambelluri, M., Tribuzio, R. & Beretta, C. (2001). Evolution
of the Ligurian Tethys: inference from petrology and
geo-chemistry of the Ligurian Ophiolites. Periodico di
Mineralogia, 70, 147-192.
- Rolfo F., Benna P., Cadoppi P., Castelli, D., Favero-Longo, S.E., Giardino, M., Balestro, G., Belluso,
E., Borghi, A, Cámara, F., Compagnoni, R., Ferrando,
S., Festa, A., Forno, M.G., Giacometti, F., Gianotti, F.,
Groppo, C., Lombardo, B, Mosca, P., Perrone, G., Piervittori, R., Rebay, G. & Rossetti, P. (2014). The Monviso massif and the Cottian Alps as symbols of the Alpine
chain and geological heritage in Piemonte, Italy. Geoheritage, in press. DOI: 10.1007/s12371-014-0097-9.
61
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Alps-Dinarides vs. Alps-Apennines transition:
changes in subduction polarity in space and time
Stefan M. Schmid
Institut für Geophysik, ETH Zürich, Switzerland
There are substantial differences between the Alps-Dinarides and the Alps-Apennines transitions. The
Alps-Dinarides transition has to do with a long-lived
change in polarity that already initiated during the opening of Alpine Tethys, contemporaneous with obduction
of the West Vardar ophiolites onto Adria. Spreading in
Alpine Tethys triggered late Jurassic obduction of Neotethys whereby Adria represented the lower plate. This
configuration was maintained until collision with Europe
(Tisza-Dacia), Adria remaining in a lower plate position
in respect to Europe until Paleogene times. During the
“Miocene revolution” the geometrical configuration of
the Alps- Dinarides transition was most severely modified: Tisza and Dacia, continental fragments of Europe,
invaded the Carpathian embayment, thereby destroying
the original along-strike New- Zealand-type subduction
polarity change. This former transform linking two opposite subduction polarities along strike is located along
the present-day Mid-Hungarian shear zone.
We propose that the situation is fundamentally different
in the Apennines. As recognized early on by Piero Elter,
the northern Apennines underwent a change in subduction polarity, which is not a primary along-strike change
but one in time affecting a volume of rocks within the
northern Apennines (Internal Ligurides) that originally
was part of the Alps (e.g. Elter 1993: “… the Internal
Ligurides can be considered an integral part of the alpine tectonic building.”), and that was later, sine Late
Oligocene time, affected by the Apennines orogeny.
Conversely, the Ligurian Alps, located in the hinterland
of the Monferrato, became part of the Apennines. The
Bacino Terziario Piemontese, sealing Western Alps and
Internal Ligurides, allows for dating the onset of Apennines orogeny in a former part of the Alps (Western Alps
and Internal Ligurides).
However, there is a controversy as to whether there
was an earlier along strike change in subduction polarity located further south, somewhere between Northern Apennines-Corsica, the latter being an integral
part of the Alps, and Sardinia-Southern Apennines
that, according to the majority of authors (e.g. La-
combe & Jolivet 2005), had opposite polarities since
at least the Eocene due to an along-strike change in
subduction polarity. On the other hand, Michard et al.
(2006), Molli (2008) and Handy et al. (2010), consider, or even favor, the possibility of a reversal in
subduction polarity that affected the entire Western
Mediterranean realm, going all the way to Calabria
and the Betic Cordillera in late Eocene to early Oligocene times. From an Alpine perspective it is argued
that the Sesia-Dent Blanche system is not part of the
Austroalpine in a tectonic sense. The Alpine subduction zone essentially becomes intra-oceanic, the Sesia- Dent Blanche merely representing an extensional
allochthon detached from Adria and floating within
the Piemonte-Liguria Ocean Adria continent transition zone (Froitzheim et al. 1996). A lack of true
continent-continent (Europe-Adria) collision in the
Western Alps, as opposed to eastern Switzerland and
Austria, would leave the east Piemonte-Ligurian basin open until Oligocene times when it started to be
obducted over the internal Ligurides due to a change
in subduction polarity, possibly affecting the entire
Western Mediterranean realm (Handy et al. (2008).
REFERENCES
- Elter, P. (1993). Detritismo ofiolitico e subduzione: riflessioni sui rapport Alpi e Appennino. Mem. Soc. Geol.
It. 49: 205-215.
- Froitzheim, N., Schmid, S.M., and Frey, M. (1996).
Mesozoic paleogeography and the timing of eclogite-facies metamorphism in the Alps: A working hypothesis.
Eclogae geol. Helv. 89: 81-110.
- Handy, M. R., Schmid, S.M., Bousquet, R., Kissling,
E. & Bernoulli, D. (2010). Reconciling plate-tectonic
reconstructions of Alpine Tethys with the geological–
geophysical record of spreading and subduction in the
Alps. Earth-Science Reviews 102: 121–158.
- Lacombe, O. & Jolivet, L. (2005). Structural and kinematic relationships between Corsica and the Pyrenees-Provence domain at the time of the Pyrenean orogeny. Tectonics 24: TC1003.
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- Michard, A., Negro, F., Saddiqi, O., Bouybaouene,
M.L., Chalouan, A., Montigny, R., Goffé, B., (2006).
Pressure–temperature–time constraints on the Maghrebide mountain building: evidence from the Rif-Betic
transect (Marocco, Spain), Algerian correlations, and
geodynamic implications. Comptes Rendus Geoscience
338: 92–114.
- Molli, G. (2008). Northern Apennine–Corsica orogenic system: an updated view. In: Siegesmund, S., Fügenschuh, B., Froitzheim, N. (Eds.), Tectonic Aspects of the
Alpine–Dinaride–Carpathian System: Geological Society, London, Special Publication 298: 413–442.
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Low-angle extensional fault systems in the Northern Apennines thrust wedge:
similarities and differences between the Tellaro and Val di Lima detachments
Fabrizio Storti(1), Fabrizio Balsamo(1), Luca Clemenzi(1), Giancarlo Molli(1, 2), Philippe Muchez(3), Rudy Swennen(3)
1 NEXT - Natural and Experimental Tectonics Research Group - Department of Physics and Eart
Sciences “Macedonio Melloni”, University of Parma, Italy
2 Department of Earth Sciences, University of Pisa, Italy
3 Department of Earth and Environmental Sciences, Heverlee, Belgium
Despite representing somehow still mechanically puzzling deformation structures, low-angle extensional fault
systems are well known in the Apenninic thrust wedge,
from the Tyrrhenian side (e.g. the Zuccale Fault) to the
external sectors (e.g. the Alto Tiberina Fault). A common
feature of these fault systems, regardless of their age, is
the eastward tectonic transport direction. In this contribution, we describe the Tellaro and Val di Lima detachments: two exhumed low-angle extensional fault systems
that affected the carbonate-dominated multilayer of the
Tuscan basinal succession (Upper Triassic to Oligocene
in age) and are now exposed in the Northern Apennines
mountain belt. We characterize the structural architecture
of the fault systems and constrain the P-T condition of the
main kinematic activity, and the paleofluid evolution of
the fault zones, by means of petrographic, mineralogical,
geochemical, and fluid inclusion analyses on fault rocks
and fault-related dolomite and calcite veins.
The Tellaro Detachment developed in the internal portion
of the Northern Apennines wedge and is well exposed
along the Tyrrhenian coastline, between Lerici and Tellaro villages. It consists of an array of anastomosed flat-lying fault zones, onto which subsidiary high-angle faults
sole down, and caused a remarkable thinning of the Tuscan succession. The extensional deformation was mostly
accommodated by the misoriented low-angle faults, with
a average tectonic transport direction toward NE and local values ranging from N010E to N080E. Synkinematic
dolomitization, brecciation, dissolution, and veining are
widespread along the near horizontal brittle shear zones.
This fault system was characterized by long-lasting kinematic activity during progressive exhumation from ~ 5 to
2 km depths, associated with a complex paleofluid evolution. Multidisciplinary analysis of the different infill generations precipitated in fault breccias and in syn-tectonic
veins indicate mixing of local- and far-sourced parent
fluids, and precipitation of calcite and dolomite cements
at different temperature and depths. The Val di Lima Detachment developed in the central portion of the Northern
Apennines wedge, and is exposed in the Lima valley, east
of the Alpi Apuane metamorphic complex. This fault system affects the right-side-up limb of a kilometric-scale
recumbent isoclinal anticline and is, in turn, affected by
superimposed folding and late-tectonic high-angle extensional faulting. Our data indicate that the low-angle fault
system was active at about 180°C and 5 km depth and
acted as a combined conduit-barrier system which affected fluid circulation within the upper crust in two ways: i)
it allowed the migration of low-salinity fluids, due to the
increased permeability along the fault zone; ii) it favored
footwall fluid overpressures, localized where an impermeable lithology (e.g. foliated cataclasite) developed in
the fault core and acted as an efficient hydraulic barrier.
Low-salinity fluid circulation in fault damage zones also
characterized the late-stage evolution of the low-angle
fault system, and was associated with the post-kinematic
recrystallization of calcite veins at shallower conditions
(~ 4 km).
Despite both fault systems were active with very shallow
eastward dip and at comparable crustal levels, the major
difference between them is their post-kinematic evolution. The Val di Lima detachment resulted from a single
extensional pulse that affected the shallow portion of the
wedge within its orogenic contractional evolution, as confirmed by the late-stage folding associated with out-ofsequence thrusting. Such extensional tectonics was triggered by the gravitational disequilibrium resulted from
thick-skinned thrusting and antiformal stacking at depth.
Fault system geometry was controlled by the favorable
orientation of weak discontinuities within the upper part
of the Tuscan succession. On the other hand, the Tellaro
Detachment is located in an area where tectonic thinning
of the shallower portion of the wedge is widespread. The
Tellaro Detachment, in particular, likely cuts through the
Punta Bianca Anticline and is dissected by the Pliocene
high-angle extensional fault system bounding to the west
the Lower Magra Valley basin. This suggests that the Tellaro Detachment formed in response to the late-orogenic tectonic thinning of the inner sector of the Northern
Apennines tectonic wedge.
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In search of Adria’s rails:
the mid-Tyrrhenian western Adria’s rail and its pivoting ligurian tip
Benedetta Treves(1) and Giuseppe Nirta(2)
(1) Istituto di Geoscienze e Georisorse, CNR, Florence Unit, Italy
(2) Department of Earth Sciences, University of Florence, Italy
Transcurrent motion goes very often undetected in the
geologic record because of the lack of clear and permanent markers that instead characterize extension
(volcanism, magnetic anomalies) and convergence
(compression, orogenic deformation). Its effect on
the upper crust is also extremely transient and easily
erased by minor components of vertical (extensional or compressional) movements. Moreover, surface
crustal deformations do not necessarily reflect directly subsurface kinematics and can be different from
the underlying deeper lithospheric strain. Strain partitioning and vertical decoupling in the lithosphere
play a crucial role in many geodynamic systems. In
the geodynamic super-puzzle of the Western Tethys/
Western Mediterranean realm, a dominant role of
transcurrent tectonics throughout the Mesozoic and
Cenozoic can explain many unsolved problems. Occurrence of major lateral displacements among the
EU, AF, IB and AD plates helps to solve the following kinematic problems and inconsistencies that
arise from a cylindrical, two-dimensional view of the
Western Mediterranean tectonics: 1) The tectonics,
orientation and geometry of the Apennine orogenic
belt are very difficult to reconcile with the EU/AF
Tertiary displacement path and plate motion directions.2) The Tyrrhenian Sea is a curious extensional basin between two converging plates. 3) Did the
Alps-Apennine junction migrate in time? Can it be
analysed through a triple point migration process of
the three plates meeting at the junction, Adria, Europe
and Iberia?4) What kind of deformation actually occurs at depth in the lithosphere under the Alps-Apennine hinge? In particular, we propose the presence
of a major crustal discontinuity, that presently runs
with NS orientation along the eastern margin of the
Corsica-Sardinia Massif. This must have acted as a
left-lateral strike-slip rail with a major role in Adria’s
700 km northern displacement in the Tertiary. In fact,
Adria’s convergence toward the European Plate, that
started in the Late Cretaceous, must have been accomplished along a major rail along its western mar-
gin. This rail (the ‘mid-Tyrrhenian rail) has a present
N-S orientation, probably resulting from counterclockwise rotation of an original NNE-SSW oriented
discontinuity, and is located along the eastern margin
of the Corsica-Sardinia block = Western margin of
the Tyrrhenian Sea.
Regarding the odd location and direction of Western Mediterranean basin extension with respect to the
northerly EU/AF motion, rotation of smaller crustal
blocks related to a deeper, decoupled, lithospheric transcurrent drag seems to be able to explain the
inconsistencies. Adopting the kinematic solution by
Viti et al., (2011), the E-W and later NE-SW left-lateral shear of the African Plate with respect to Europe
possibly caused the rotation of several smaller crustal
blocks located in between: Balearic, Corso-Sardinian,
Adriatic. A ‘locked’ corner of the Adriatic block (the
NW one) acted as pivot and Euler pole for Adria’s
rotation, splitting this plate into two portions: to the
north it overthrust the European crust, to the SW it underthrust the Iberian margin. A transform cut between
the two portions is a necessary tectonic requirement
to accomplish this dynamics, but and it’s difficult to
locate at the surface and so far went unrecognized.
A triple point analysis of the motion of EU/AD/IB,
meeting at the locked corner, helps unravel the older geodynamic history, but for the Tertiary evolution
of the Alps-Apennine junction, the amount of crustal rotation and deformation prevents a simple vector analysis of the plate boundaries. The curved arms
of the Alpine and Apenninic belts, joining above the
Gulf of Genova in a sort of spiral torsion, strongly
suggest a vortex-style deformation related to the anticlockwise rotation of Adria about the ‘Ligurian Knot’
(Laubscher et al., 1992). We present a filmstrip of
many original solutions that have been proposed in
the past for solving the puzzling geodynamic junction between Alps and Apennines. Among them, still
stands the model by Elter and Pertusati (1973) that
gave us a powerful graphic solution on which to work
and think.
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REFERENCES
- Elter, P. & Pertusati, P.C. (1973). Considerazioni sul
limite Alpi-Appennino e sulle relazioni con l’arco
delle Alpi occidentali. Mem. Soc. Geol. It., 12, pp.
359-375.
- Laubscher, H., G. C. Biella, R. Cassinis, R. Gelati, A.
Lozej, S. Scarascia, & I. Tabacco, (1992). The collisional knot in Liguria. Geologische Rundschau 06/1992;
81(2), pp. 275-289.
- Viti, M. , Mantovani, E. , Babbucci, D. & Tamburelli, C., (2011). Plate kinematics and geodynamics in
the Central Mediterranean. Journal of Geodynamics,
Vol.51(2), pp.190-204 .
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state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Evidences of late Miocene low-angle extensional tectonics affecting the
western Northern Apennines orogenic wedge
Paolo Vescovi, Mirko Carlini, Andrea Artoni, Luca Clemenzi, Luigi Torelli
Physics and Earth Sciences Department “Macedonio Melloni”, University of Parma, Italy
The present work investigates the Neogene structural
evolution of the western portion of the Northern Apennines from the Tyrrhenian coast of eastern Liguria to the
Po Plain foothills, including the key areas of Magra and
Taro river valleys (Fig. 1). Within this area, the internal
portion of the mountain belt shows a complex structural
architecture with remarkable lateral variability. To the SE,
well-developed Plio-Pleistocene high-angle extensional
faulting (Bernini e Papani, 2002) is associated with wide
exposures of Paleogene-Neogene foredeep deposits and
the underlying Mesozoic carbonate-dominated sedimentary sequences of the Tuscan paleogeographic domain.
On the contrary, to the NW and NE, where the extensional fault system gradually decreases in offset and length,
the Paleogene-Neogene Tuscan foredeep deposits are
exposed only within the M.te Zuccone tectonic window.
Figure 1 - structural scheme of the
western Northern Apennines. Modified after Bernini et al. (1997).
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The analysis of two regional-scale seismic lines integrated
with field geological and structural data (Fig. 1) allowed
to recognize evidences of low-angle extensional tectonics which affected the western Northern Apennines orogenic wedge at different structural levels and predates the
Plio-Pleistocene high-angle extensional faults. At shallow
levels (< 1 km), low-angle normal faulting is located at the
base of the Epiligurian wedge-top basin deposits (Artoni
et al., 2006). At slightly deeper structural levels (~ 1 to 4
km), low-angle extensional faults occur in the Ligurian and
Subligurian allochthonous units. These faults downthrown
the uppermost Ligurian unit (i.e. Gottero Unit, Figs. 1, 2)
directly onto the deeper foredeep units (Elter and Schwab,
1959) and they realize a tectonic thinning estimated in ~1-4
km (LANF in Carlini et al, 2013). At deeper structural levels
(~5 km), low-angle extensional fault systems have thinned
the carbonate-dominated Mesozoic sequence of the Tuscan
succession (Clemenzi et al., submitted; Storti, 1995). In all
these cases, the low-angle extensional tectonics indicates
top-to-NE tectonic transport direction. At shallow structural
levels (<1 km down to ~4 km), low-angle tectonic thinning
has been constrained to an age interval comprised between
middle Miocene (age of the youngest foredeep units buried
underneath the allochthonous units) and late Miocene (age
of the oldest deposits sealing the allochthonous units at the
Po Plain foothills). At deeper structural levels, the low-angle extensional faulting postdates the middle-late Miocene
thermal peak associated with the maximum tectonic burial
of the Tuscan succession and is post-dated by Plio-Pleistocene high-angle extensional faulting (Fellin et al., 2007 and
references therein).
All the previously and newly recognized cases of low-angle extensional tectonics presented in this study have been
framed in a consistent regional framework and interpreted
as episodes of tectonic thinning which affected the western Northern Apennines during the late Miocene. This late
Miocene low-angle extension would have been triggered
by the mechanical and gravitationally instability resulting
from orogenic wedge over-thickening related to the deep
contractional deformations. During the Plio-Pleistocene
times, thick-skinned tectonics migrated toward NE as testified by seismic “basement” units involved in the deformations (Argnani et al, 2003); this younger growth of the
orogenic wedge enhanced the high-angle extensional faulting (Bernini e Papani, 2002) and dismembered the earlier
low-angle extensional faults.
Figure 2 - schematic sections across the
western Northern Apennine showing the
late Miocene low-angle extensional fault
affecting the Ligurian and Epiligurian
units. See Fig. 1 for the location of the
schematic sections.
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The late Miocene low-angle extensional tectonics represent a key feature of the Northern Apennines: it played a
fundamental role in the development of the structural architecture of the mountain belt.
REFERENCES
- Argnani, A., Barbacini, G., Bernini,M., Camurri, F.,
Ghielmi,M., Papani, G., Rizzini, F., Rogledi, S., Torelli,
L., (2003). Gravity tectonics driven by Quaternary uplift
in the Northern Apennines: insights from the La Spezia–
Reggio Emilia geo-transect. Quat. Int. 101–102, 13–26.
- Artoni, A., Bernini, M., Vescovi, P., Lorenzi, U., Missorini, E., (2006). Estensione alla sommità del cuneo
orogenico appenninico: contatti tettonici elisionali nella
Successione epiligure di M. Barigazzo (Appennino settentrionale, prov. di Parma). Rend. Soc. Ital., 2, 69–72.
- Bernini, M., Papani, G., (2002). La distensione della
fossa tettonica della Lunigiana nord-occidentale (con
Carta Geologica alla scala 1:50000). Boll. Soc. Geol. It.,
121, 313-341.
- Bernini, M., Vescovi, P., Zanzucchi, G., (1997). Schema strutturale dell’Appennino Nord-Occidentale. L’Ateneo Parmense Acta Naturalia, 33, 43-54.
- Carlini, M., Artoni, A., Aldega, L., Balestrieri M.
L., Corrado S., Vescovi P., Bernini M., Torelli, L.,
(2013). Exhumation and reshaping of far-travelled/
allochthonous tectonic units in mountain belts.
New insights for the relationships between shortening and coeval extension in the western Northern
Apennines (Italy). Tectonophysics, 608, 267–287.
- Clemenzi, L., Molli, G., Storti, F., Muchez, P.,
Swennen, R., Torelli, L. (submitted). Extensional
deformation structures within a convergent orogen:
The Val di Lima low-angle normal fault system
(Northern Apennines, Italy). Journal of Structural
Geology
- Elter, P., Schwab, K., (1959). Note illustrative
alla carta geologica all’1-50000 della regione Carro-Zeri-Pontremoli. Boll. Soc. Geol. Ital. 78, 157–
187.
- Fellin, M.G., Reiners, P.W., Brandon, M.T.,
Wüthrich, E., Balestrieri, M.L., Molli, G., (2007).
Thermochronologic evidence for the exhumational
history of the Alpi Apuane metamorphic core complex, northern Apennines, Italy. Tectonics 26.
- Storti, F., (1995). Tectonics of the Punta Bianca Promontory: Insights for the evolution of the
Northern Apennines, Northern Tyrrhenian Sea basin. Tectonics, 14, 832-847.
69
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Structural analysis of out-of-sequence thrust faults in western Sorrento
Peninsula (southern Apennines, Italy)
Stefano Vitale(1), Federico Borreca(2), Sabatino Ciarcia(1), Bilal El Ouaragli(3), Fabio Laiena(1), Francesco
D’Assisi Tramparulo(1)
(1) Dipartimento di Scienze della Terra, dell’Ambiente e delle Risorse (DiSTAR), Università di Napoli
Federico II, Italy
(2) Agenzia Regionale Campana Difesa Suolo (ARCADIS), Napoli, Italy
(3) Department of Earth Sciences, F.S.T.-Tangier, University of Abdelmalek Essaadi, Morocco
INTRODUCTION
This work is aimed to analyze the out-of-sequence thrust
faul crosscutting the Apennine Platform Unit and the unconformable upper Tortonian wedge-top-basin deposits
cropping out in the western sector of the Sorrento Peninsula (Fig. 1). These thrusts can be correlated to other outof-sequence structures spread out in the whole southern
Apennine chain. According to their wide diffusion and
the constant vergence toward the northern sectors, it is
possible to ascribe these structures to a well-defined tectonic stage during the Apennine orogenic evolution, occurred in the Upper Messinian-Lower Pliocene interval.
GEOLOGICAL SETTING
The backbone of the southern Apennines (Fig.1) is
made of Apennine Platform carbonates (Mostardini
and Merlini, 1986) including a large variety of sedimentary facies ranging from basin to slope, margin and
platform (e.g. Vitale & Ciarcia, 2013 and references
therein), tectonically sandwiched between the basin
successions of the Ligurian Accretionary Complex
(LAC; Ciarcia et al., 2012; Vitale et al., 2013a,b), on
the top, and the Lagonegro-Molise Basin deposits (Mostardini & Merlini, 1986) on the bottom, the latter overlying the buried Apulian Platform carbonates (Fig. 1).
Figure 1. Tectonic map of the southern Apennines (modified after Vitale & Ciarcia, 2013)
and cross section (modified after Mazzoli et
al., 2008).
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The southern Apennines formed as consequence of the
closure of the Ligurian Basin, characterized by the transition from oceanic to thinned continental lithosphere,
with the subduction of its westernmost sector under the
European Plate starting from the Eocene time (Vitale &
Ciarcia, 2013) and the successive frontal accretion of the
easternmost sector in the Aquitanian-Burdigalian interval with the detachment of the Nord-Calabrese, Parasicilidi and Sicilidi Units (Ciarcia et al., 2012 and references therein) from their pre-Eocene basements. Currently
the latter successions together with the VLT-HP Frido
Unit (Vitale et al., 2013a) form the LAC widely spread
out in the whole southern Apennines (Fig. 1). The
Apennine Platform was included in the tectonic wedge
from the Middle-Late Miocene by means of a dominant
thick-skinned tectonics (Vitale & Ciarcia, 2013) and
finally overthrust onto the successions of the Lagonegro-Molise Basin. The latter was definitively closed before the upper part of the Early Pliocene with the activation of several thrust sheet imbrications by means of a
thin-skinned tectonics and together the whole orogenic
chain overthrust onto the Apulian Platform carbonates
(Ciarcia & Vitale, 2013). The latter realm was deformed
by ramp-dominated thrust faults from the Early Pliocene
to Middle Pleistocene, probably as reactivation of previous normal structures (Shiner et al., 2004).
WESTERN SORRENTO PENINSULA
The western Sorrento Peninsula (Fig. 2) mainly consists
of Cretaceous shallow water limestones covered by Burdigalian-Serravallian foredeep calcarenites and sandstones (Nerano Fm.). The succession is unconformably
sealed by wedge-top basin deposits of the upper Tortonian Punta Lagno Fm. (De Blasio et al., 1981) made of
calcareous conglomerates, calcareous and varicoloured
clay olistostromes and olistoliths (amongst others from
the LAC units), marls and sandstones.
The structural survey marked a complex geometry characterized by a main flat-lying thrust fault running from
the Cala di Mitigliano to Capo di Sorrento (Fig. 2) with a
displacement of at least 5 km joining to a ramp at base of
the Mt. San Costanzo characterized by a small displacement. The main thrust is well exposed in the Cala di
Mitigliano where a main sub-horizontal plane outcrops
with pervasive slickensides indicating an N-tectonic
transport and several secondary thrust and back-thrust
Figure 2 - (a) Geological map of
Western Sorrento Peninsula (modified after ISPRA, 2014). (b) Cross
section.
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planes and rare folds. The main thrust superposes the Cretaceous limestones onto the Miocene sandstones and calcarenites, the latter pervasively deformed by Riedle shear
planes with calcite fibres indicating a northward tectonic
transport. This main thrust fault crops out also in the Punta Lagno and Marina di Puolo forming small klippen. In
these areas several secondary thrust and back-thrust faults
occur. In the Marina di Puolo and Capo di Sorrento areas this thrust deformed the foredeep sandstones and the
unconformable upper Tortonian Punta Lagno Fm. with
the setup of thrust faults, related folds and rarely with an
associated crenulation cleavage. The main thrust at base
of Mt. San Costanzo is well exposed in the southernmost
sector of the Cala di Mitigliano (Fig. 2). Here this structure shows a high dip angle and overturned strata in the
footwall. Thrust faults and Riedle shear planes indicate a
northward tectonic transport.
REFERENCES
- Ciarcia, S. & Vitale, S., (2013). Sedimentology, stratigraphy and tectonics of evolving wedge-top depozone:
Ariano Basin, southern Apennines, Italy. Sedimentary
Geology, 290, 27-46.
- Ciarcia, S., Mazzoli, S., Vitale, S. & Zattin, M., (2012).
On the tectonic evolution of the Ligurian accretionary
complex in southern Italy. Geological Society of America Bulletin 124, 463–483.
- De Blasio, I., Lima, A., Perrone, V. & Russo, M.,
(1981). Nuove vedute sui depositi miocenici della Penisola Sorrentina. Bollettino della Societa Geologica Italiana 100, 57–70.
- ISPRA, 2014. Carta Geologica d’Italia alla scala
1:50.000, Foglio 466 ‘Sorrento’.
- Mazzoli, S., D’Errico, M., Aldega, L., Corrado, S.,
Invernizzi ,C., Shiner, P. & Zattin, M. (2008). Tectonic burial and ‘young’ (< 10 Ma) exhumation in
the southern Apennines fold and thrust belt (Italy).
Geology 36, 243-246.
- Mostardini, F. & Merlini, S., (1986). Appennino
centro-meridionale: sezioni Geologiche e proposta
dimodello strutturale.Memorie della Società Geologica Italiana 35, 177–202.
- Shiner, P., Beccacini, A. & Mazzoli, S., (2004).
Thin-skinned versus thick-skinned structural models
for Apulian Carbonate Reservoirs: constraints from
the Val D’Agri Fields. Marine and Petroleum Geology 21, 805–827.
- Vitale, S. & Ciarcia, S., (2013). Tectono-stratigraphic and kinematic evolution of the southern
Apennines/Calabria-Peloritani Terrane system (Italy). Tectonophysics, 583, 164–182.
- Vitale, S., Fedele, L., Tramparulo, F. d’A., Ciarcia,
S., Mazzoli, S. & Novellino, A., (2013a). Structural
and petrological analysis of the Frido Unit (southern
Italy): new insights into the early tectonic evolution
of the southern Apennines- Calabrian Arc system.
Lithos, 168-169, 219-235.
- Vitale, S., Ciarcia, S. & Tramparulo, F. d’A.,
(2013b). Deformation and stratigraphic evolution
of the Ligurian Accretionary Complex in the southern Apennines (Italy). Journal of Geodynamics, 66,
120-133.
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Multiscale structural analysis supporting petrologic modelling to infer
HP/UHP mineral assemblages of subducted rodingites from the upper
Valtournanche, Western Alps, Italy
Davide Zanoni(1), Gisella Rebay(2), Maria Iole Spalla(1, 3)
(1) Dipartimento di Scienze della Terra “A. Desio”, Università degli Studi di Milano, Italy
(2) Dipartimento di Scienze della Terra e dell’Ambiente, Università degli Studi di Pavia, Italy
(3) C.N.R.-I.D.P.A. sezione di Milano, Italy
Rodingites associated with serpentinite massifs are
generally considered the products of a metasomatic ocean floor process (e.g. O’Hanley et al., 1992;
Palandri & Reed, 2004; Panseri et al., 2008; Bach &
Klein, 2009). Even if rodingitisation can take place in
subduction environments, as in the case of the Othrys
massif (Tsikouras et al., 2009), re-structuration and
metamorphic transformations involving rodingites
within a convergent system are generally neglected.
Former studies on rodingites from the Alpine belt
(Weinschenk, 1894; Cornelius, 1912; Staub, 1915;
Rondolino, 1937; Amstutz, 1962), described rodingitic mineral assemblages as metasomatic relicts escaping the Alpine regional metamorphism until when Dal
Piaz (1967) pointed out that rodingites were widely
re-equilibrated during Alpine HP metamorphic evolution together with their country rocks. Successively
rodingites affected by HP re-equilibration have been
described in other portions of the Zermatt-Saas Zone
(Pfulwe and M. Avic regions), in the Ligurian Alps
(Voltri Massif) and in southern Spain (Piccardo et al.,
1980; Messiga et al., 1983; Puga et al., 1999; Li et al.,
2008; Ferrando et al., 2010).
In order to define the HP mineral assemblages in
the boudinaged rodingites of the upper Valtournanche, embodied in HP/UHP partly de-hydrated serpentinites of Zermatt-Saas Zone (Rebay et al., 2012),
we undertook a multiscale combined structural and
metamorphic analysis. On the basis of different associations of minerals and their modal amount, three
types of rodingite are distinguished: epidote-, garnet-chlorite-clinopyroxene-, and vesuvianite-bearing
rodingites (Zanoni et al., 2012). Up to cm-sized relict clinopyroxene porphyroclasts point out that these
rodingites derive from ocean floor metasomatism of
former gabbro dykes intruded in mantle rocks. The
deformation history recorded in the serpentinites affects also rodingites, as proven by continuous struc-
tural correlation in the field. All rocks record, after the
ocean floor history, four stages of ductile deformation
and the first three groups of structures are associated
with new mineral growth. D1 and D2 developed under
HP to UHP conditions and D3 under lower pressure
conditions. The following syn-D2 assemblages in
rodingites are interpreted as developed under the same
HP/UHP conditions already inferred in serpentinites
(2.5 ± 0.3GPa and 600 ± 20°C, Rebay et al., 2012),
for the Alpine subduction: epidoteII, clinopyroxeneII,
Mg-chloriteII, titaniteI, ± garnetII, ± tremoliteI in
epidote-bearing rodingites; Mg-chloriteII, garnetII,
clinopyroxeneII, ± vesuvianiteII, ± opaque minerals,
in garnet-chlorite-clinopyroxene-bearing rodingites;
vesuvianiteII, Mg-chloriteII, clinopyroxeneII, garnetII, ± titaniteI, ± epidoteI in vesuvianite-bearing
rodingites. Thermodynamic modelling in epidoteand garnet-chlorite-clinopyroxene-bearing rodingites quantitatively confirms the P-T range for climax
conditions inferred in the associated serpentinites.
Pre-D1 mineral relicts such as Cr-rich spinel and cmsized clinopyroxene porphyroclasts are interpreted as
magmatic vestiges of the rodingitised gabbro dykes,
whereas Cr-rich garnet and Cr-Ti-Ca-rich vesuvianite
as developed during oceanic metasomatism. Distinct
chemical compositions characterise the same minerals recrystallised during the Alpine subduction.
Multiscale structural analysis shows that the dominant structural and metamorphic imprint recorded by
the Valtournanche eclogitised rodingites developed
during the Alpine subduction and that, in the favourable bulk composition (Ca-rich), vesuvianite is stable
up to the estimated P-climax metamorphic conditions.
REFERENCES
- Amstutz, A. (1962). Notice puor une carte géologique de
la Vallée de Cogne et de quelches autres espaces au Sud
d’Aoste. Archives des Sciences de Genève, 15, 1-104.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
- Bach, W. & Klein, F. (2009). The petrology of seafloor rodingites: Insights from geochemical reaction
path modeling. Lithos, 112, 103-117.
- Cornelius, H.P. (1912). Petrographische Untersuchengen in den Bergen zwischen Septimer und Julierpass.
Neues Jahrbuch für Mineralogie, Gelogie und Paläontologie, 35, 374-498.
- Dal Piaz, G.V. (1967). Le “granatiti” (rodingiti L. S.)
nelle serpentine delle Alpi occidentali italiane. Memorie della Società Geologica Italiana, 6, 267-313.
- Ferrando, S., Frezzotti, M.L., Orione, P., Conte, R.C.
& Compagnoni, R. (2010). Late-Alpine rodingitization
in the Bellecombe meta-ophiolites (Aosta Valley, Italian Western Alps): evidence from mineral assemblages
and serpentinization-derived H2-bearing brine. International Geology Review, 52(10-12), 1220-1243.
- Li, X.P., Rahn, M. & Bucher, K. (2008). Eclogite
facies metarodingites – phase relations in the system
SiO2-Al2O3-Fe2O3-FeO-MgO-CaO-CO2-H2O: an
example from the Zermatt-Saas ophiolite. Journal of
Metamorphic Geology, 26, 347-364.
- Messiga, B., Piccardo, G.B. & Ernst, W.G. (1983).
High- pressure eo-alpine parageneses developed in
magnesian metagabbros, Gruppo di Voltri, Western Liguria, Italy. Contributions to Mineralogy and Petrology, 83, 1-15.
- O’Hanley, D.S., Schandl, E.S. & Wicks, F.J. (1992).
The origin of rodingites from Cassiar, British Columbia, and their use to estimate T and P(H2O) during serpentinization. Geochimica et Cosmochimica Acta, 56,
97-108.
- Palandri, J.L. & Reed, M.H. (2004). Geochemical
models of metasomatism in ultramafic systems: Serpentinization, rodingitization, and sea floor carbonate
chimney precipitation. Geochimica et Cosmochimica
Acta, 68(5), 1115-1133.
- Panseri, M., Fontana, E. & Tartarotti, P. (2008), Evolution of rodingitic dykes: metasomatism and metamorphism in the Mount Avic serpentinites (Alpine ophiolites, Southern Aosta Valley). Ofioliti, 33(2), 165-185.
- Piccardo, G.B., Messiga, B. & Cimmino, F. (1980).
Antigoritic serpentinites and rodingites of the Voltri
Massif; some petrological evidences for their evolutive
history. Ofioliti, 5(1), 111-114.
- Puga, E., Nieto, J.M., Díaz de Federico, A., Bodinier,
J.L. & Morten, L. (1999). Petrology and metamorphic
evolution of ultramafic rocks and dolerite dykes of the
Betic Ophiolitic Association (Mulhacén Complex, SE
Spain): evidence of eo-Alpine subduction following an
ocean-floor metasomatic process. Lithos, 49, 23-56.
- Rebay, G., Spalla, M.I. & Zanoni, D. (2012). Interaction of deformation and metamorphism during subduction and exhumation of hydrated oceanic mantle: Insights from the Western Alps. Journal of Metamorphic
Geology, 30, 687-702.
- Rondolino, R. (1937). Sopra alcuni minerali della Valtournanche (Valle d’Aosta). Periodico di Mineralogia,
8, 53-56.
- Staub, R. (1915). Petrographische Untersuchungen im
westlichen Berninagebirge. Zürcher & Furrer, Zürich.
Tsikouras, B., Karipi, S., Rigopoulos, I., Perraki, M., Pomonis, P. & Hatzipanagiotou, K. (2009). Geochemical processes and petrogenetic evolution of rodingite
dykes in the ophiolite complex of Othrys (Central
Greece). Lithos, 113: 540-554.
- Weinschenk, E. (1894). Beiträge zur Petrographie
der östlischen zentralalpen, speziell des Gross-Venedigerstokes. I. Über die Peridotite und die aus ihnen
hervorgegangenen Serpentingesteine. Genetischer
Zusammenhang derselben mit den sie begleitenden
Minerallagerstätten. Abhandlung bayerische Akademie
Wisseschaften, 18, 651-713.
- Zanoni, D. Rebay, G., Bernardoni, J. & Spalla, M.I.
(2012). Using multiscale structural analysis to infer
high-/ultrahigh-pressure assemblages in subducted
rodingites of the Zermatt-Saas Zone at Valtournanche,
Italy. In: M. Zucali, M.I. Spalla, & G. Gosso (Eds.),
Multiscale structures and tectonic trajectories in active
margins. Journal of the Virtual Explorer, Electronic Edition, 41, paper 6.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
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Strain and reaction-rate partitioning mapping in the Mombarone Mt. Mucrone area (Sesia Lanzo Zone, Italian Western Alps)
Michele Zucali(1, 2), Francesco Delleani(1), M. Iole Spalla(1, 2), Guido Gosso(1, 2)
(1) Dipartimento di Scienze della Terra “A. Desio”, Università degli Studi di Milano, Italy
(2) CNR-IDPA, Milano, Italy
Permian intrusive bodies and metasediments of the Mt.
Mucrone – Mt. Mars – Mombarone area locally display
granulite to amphibolite pre-Alpine metamorphic imprint, preserved within the widely re-equilibrated volumes, under eclogite-facies conditions during the Cretaceous. They are now part of the Eclogitic Micaschists
Complex of the Sesia-Lanzo Zone in the Alpine HP metamorphic belt of the Western Alps. The purpose of this
contribution is to illustrate the technique for mapping
the strain and reaction rate partitioning in a polymetamorphic and polydeformed terrain, as that surfacing
along the Mt. Mucrone – Mt. Mars – Mombarone divide. Results have been synthesised in terms of deformation history and associated metamorphic evolution
on a solid-type of map at original scale at 1:10.000 and
1:5.000, with the purpose to quantitatively evaluate the
structural and metamorphic memory of rocks forged
during a continental thinning and successively deeply
involved in the Alpine subduction system.
Seven successive stages of deformation have been recognized (Delleani et al., 2013; Zucali, 2002) showing
associated metamorphic imprints evolving from eclogite (D1 to D3) and blueschist facies (D4), developed
during the active subduction of the Alpine oceanic crust,
to greenschist facies assemblages (D5 to D7) consequent to the Alpine continental collision.
The combined structural and petrologic studies made
possible to correlate the degree of fabric evolution
and metamorphic transformation at the map scale and
highlight that strain-partitioning is a critical factor controlling reaction progress.
More in detail, relationships between Fabric Evolution
Degree (FED) and reaction progress in different lithotypes suggests that differences in mineral compositions
of protoliths and original textures can exert an influence
on the reaction progress when FED remains low. The
mosaic of successive deformation imprints visualised
in the maps indicate that the High Deformation stage
represents a threshold after which deformational and
metamorphic effects proportionally increase up to the
total replacement of pre-existing minerals where new
fabrics evolved up to the stage of a continuous foliation,
in agreement with similar observations in other Alpine
areas (e.g. Salvi et al., 2010). These results focus on the
role of strain energy in catalysing metamorphic reactions. In addition, our observations indicate that where
the fabric evolution remains lower than HD the thermal
regime, as well original mineral rock composition and
fabric evolution, can significantly influence the degree
of metamorphic transformation: for the same FED, the
metamorphic reaction progress is more evolved during
D2 (eclogite facies) or during D5 (greenschist facies)
than during D4 (blueschist facies).
REFERENCES
- Delleani, F., Spalla, M.I., Castelli, D. & Gosso, G.
(2013). A new petrostructural map of Monte Mucrone
metagranitoids (Sesia-Lanzo Zone, Western Alps). Journal of Maps, 9, 410-424.
- Salvi, F., Spalla, M.I., Zucali, M. & Gosso, G. (2010).
Three- dimensional evaluation of fabric evolution and
metamorphic reaction progress in polycyclic and polymetamorphic terrains: a case from the Central Italian
Alps. Geological Society of London Special Publications, 332, 173-187.
- Zucali, M. (2002). Foliation map of the “Eclogitic
Micaschists Complex” (M. Mucrone-M.Mars-Mombarone, Sesia-Lanzo Zone, Italy). Memorie di Scienze
Geologiche, Padova, 54, 87-100.
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
Index
- ARGNANI A. - Collision, collapse and delamination: the making of the Alps-Apennine
connection
..................................................................................................................... ......
3
- BALBI P., ELTER F.M., ARMADILLO E., PIAZZA M. - A new stratigraphic and tectonic model of the south eastern Monte Antola unit and its relationship with the Monte
Gottero Unit (Eastern Liguria) .................................................................................................
5
- BALESTRO G., FESTA A., TARTAROTTI P. - Broken and dismembered formations
in the Monviso Meta-ophiolite Complex (Western Alps) .................................................. ......
6
- BARALE L., BATTAGLIA S., BERTOK C., D’ATRI A., ELLERO A., LEONI L.,
MARTIRE L., PIANA F. - Geological setting of the southern termination of the western
Alps arc (Maritime and western Ligurian Alps, NW Italy) ............................................. ......
8
- BARRECA G., MONACO C.- Geological and geophysical evidences for diapirism in
South-Eastern Sicily (Italy) and implications on paleo-tectonics of the Western Ionian
Domain .....................................................................................................................................
10
- BERNOULLI D. - The concept of ophiolites from Alexandre Brogniart to Piero Elter .......
12
- BETTELLI G., PANINI F., REMITTI F., VANNUCCHI P. - Reconciling the geology of
the Emilia Apennines and Tuscany across the Livorno-Sillaro lineament, Northern Apennines, Italy ...............................................................................................................................
13
- BONATTI E. - Piero Elter: from the Apennines to the Atlantic .............................................
15
- CERRINA FERONI A., PUCCINELLI A. - The geological sheet n° 261 – Lucca ( CARG):
main results and some suggestion ..................................................................................................
16
- CORSI B., ELTER F.M., PIAZZA M. - The Portofino conglomerate (Eastern Liguria):
stratigraphic notes ............................................................................................................... ......
18
- DAL PIAZ G.V. - Struttura ed evoluzione della catena alpina: dallo Structural Model of
Italy al Progetto Crop ed ai loro sviluppi ..................................................................................
19
- DECARLIS A., MANATSCHAL G., HAUPERT I, MASINI E. - The tectono-stratigraphic evolution of distal magma-poor rifted margins: examples from the Alpine Tethys,
the E-Indian and Newfoundland-iberia rifted margins ..............................................................
21
- ELLERO A., LOPRIENO A. - Ophiolitic units of the Northern Apennines as a tool to
unravel schistes lustres stratigraphy of the western Alps and their geodynamic context:
the Urtier Valley example, Cogne, Aosta Valley .......................................................................
22
- ELTER F.M., GAGGERO L., PANDELI E. - The late-Variscan tectonic barriers: the
beginning of alpine Wilson cicle? .............................................................................................
24
76
Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
- FESTA A., PINI G.A., DILEK Y. - Olistostromes and mélanges in the External Ligurian
Units in Monferrato (NW Italy) .......................................................................................... ......
25
- GIUSTI R., PANDELI E., ELTER F.M. - Ductile shear zone in the termo-metamorphic aureole
of Monte Capanne: data from Cavoli-Colle Palombaia area (south-western Elba Island, Italy) .........
26
- HOBBS N., LUVISI E., MARRONI M., MENEGHINI F., PANDOLFI L. - The role
of the Ottone-Levanto Line in the geodynamic evolution of the Northern Apennine: evidences from the high Sturla Valley, Liguria, Italy .....................................................................
28
- KRAUS R.K., ELTER F.M., ELENA E., SOLARINO S. - Distribution of differing
stress regimes in the western central Alps controlled by inner arc bending? .............................
30
- LOPRIENO A., ELLERO A. - Structural analysis of the nappe stack in the Urtier Valley,
Cogne (Western Alps) ................................................................................................................
31
- MAINO M., STUART F.M., CERIANI A., DECARLIS A., di GIULIO A., SENO S.,
SETTI M. - Zircon (U-Th)/He dating of the penninic basal thrust .............................................
32
- MALAVIEILLE J.- Impact of surface processes and structural heritage on the structure
and dynamics of orogenic wedges : insights from Taiwan ........................................................
33
- MARCHI A., PANDOLFI L., CATANZARITI R. - The basal part Modino unit succession under the belt-foredeep system of the Northern Apennines (Italy) .....................................
35
- MARINI F., PANDELI E., TONGIORGI M. - The late Carboniferous-Permian successions of the Northern Apennines: new data from the contact between San Lorenzo Schists
and Asciano Breccias and conglomerates in the Pisani Mts. inlier (Tuscany, Italy) ................
36
- MAROTTA A.M., CONTE K., RODA M., SPALLA M.I. - Thermo-mechanical numerical model of the transition from continental rifting to oceanization: the transition from
Permian-triassic thinning to oceanisation in the Alpine chain .................................................
38
- MONTOMOLI C., CAROSI R., LANGONE A., BORSANI A., IACCARINO S. - Lower Miocene contractional shearing in the Massa Unit (Northern Apennines, Italy): in situ
U-Th-Pb dating of monazite ......................................................................................................
39
- MUSUMECI G., MASSA G., PIERUCCIONI D., MAZZARINI F. - Out of sequence
thrust in the inner zone of Northern Apennines: insight from Elba Island nappe stack ...........
41
- MUTTI E. - Paleogeographic problems of the Eocene foreland basin of the South-central Pyrenees ..............................................................................................................................
43
- NOVELLINO R., PROSSER G., VITI C., SPIESS R., AGOSTA F., TAVARNELLI E.,
BUCCI F. - Microstructural evidence of weakening mechanisms developed along incipient low-angle normal faults in pelagic limestones (Southern Apennine, Italy) ................ ......
44
- ORTOLANO G., TRIPODI V., CIRRINCIONE R., CRITELLI S., MUTO F., VISALLI
R. - The role of strike-slip tectonics in the early to late formation of the southern Calabrian
Alpine-Apennine chain system. (Calabria, Southern Italy) .......................................................
45
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Meeting in memory of Piero Elter - The relationships between Northern Apennine and western Alps:
state of the art fifty years after the “Ruga del Bracco” - Pisa, June 26-27, 2014
- PANDELI E., ELTER F.M., TOKSOYKÖKSAL F., PRINCIPI G. - Relationships between the Kirşehir Massif and the Sakarya Zone (Turkey): geological and petrographical
data from the Ankara-Erzincan suture and surroundings ..........................................................
48
- PANDOLFI L., BOSCHI C., LUVISI E., ELLERO A., MARRONI M., MENEGHINI F. - Seep carbonates and chemosynthetic coral communities in the Bocco Shale (Internal Ligurides, Northern Apennine, Italy) as record of trench-slope limit in the early
Paleocene alpine accretionary wedge................................................................................. ......
50
- PEACOCK D.C.P. - Explosion breccias ..................................................................................
51
- PEACOCK D.C.P., CASINI G., ANDERSON M.W., TAVARNELLI E. - Stresses, overpressure and transient strike-slip during tectonic inversion .....................................................
52
- PIAZZA A., ARTONI A. - The epiligurian basin in the middle Enza Valley (Northern
Apennines, Italy): evidences of a Priabonian-Serravallian syn-depositional polyphased
deformation zone .......................................................................................................................
53
- PRINCIPI G., TREVES B. - Evolution of the Alps-Apennine boundary: EU/IB/AD
transcurrence leading to a crustal vortex ....................................................................................
57
- ROLFO F., BALESTRO G., BORGHI A., CASTELLI D., FERRANDO S., GROPPO
C., MOSCA P., COMPAGNONI R. - Walking through the Tethys in the Monviso ophiolite (Piemonte, Italy) ..................................................................................................................
59
- SCHMID S.M. - Alps-Dinarides vs. Alps-Apennine transition: changes in subduction
polarity in space and time ..........................................................................................................
62
- STORTI F., BALSAMO F., CLEMENZI C., MOLLI G., MUCHEZ P., SWENNEN R. Low-angle extensional fault systems in the Northern Apennines thrust wedge: similarities
and differences between the Tellaro and Val di Lima detachments ..........................................
64
- TREVES B., NIRTA G. - In search of Adria’s rails: the mid Tyrrhenian western Adria’s
rail and its pivoting ligurian tip .................................................................................................
65
- VESCOVI P., CARLINI M., ARTONI A., CLEMENZI L., TORELLI L. - Evidences of
late Miocene low-angle extensional tectonics affecting the western Northern Apennines
orogenic wedge ................................................................................................................... ......
67
- VITALE S., BORRECA F., CIARCIA S., el OUARAGLI B., LAIENA F., D’ASSISI
TRAMPARULO F. - Structural analysis of out-of-sequence thrust faults in western Sorrento Peninsula (Southern Apennines, Italy) .............................................................................
70
- ZANONI D., REBAY G., SPALLA M.I. - Multiscale structural analysis supporting petrologic modelling to infer hp/uhp mineral assemblages of subducted rodingites from the
upper Valtournanche, western Alps, Italy ........................................................................... ......
73
- ZUCALI M., DELLEANI F., SPALLA M.I., GOSSO G. - Strain and reaction-rate partitioning mapping in the Mombarone - Mt. Mucrone area (Sesia Lanzo zone, italian western Alps) ....................................................................................................................................
75
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