Brittle-ductile deformation and kinematics during
exhumation of metamorphic complexes below
detachments: examples from Sifnos and Syros Islands
(Greece)
Gioavanni Cardello, Vincent Roche, Valentin Laurent, Laurent Jolivet
To cite this version:
Gioavanni Cardello, Vincent Roche, Valentin Laurent, Laurent Jolivet. Brittle-ductile deformation and kinematics during exhumation of metamorphic complexes below detachments:
examples from Sifnos and Syros Islands (Greece). European Geosciences Union General Assembly 2014, Apr 2014, Vienne, Austria. EGU, 16, pp.EGU2014-8867, 2014, Geophysical Research
Abstracts.
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Geophysical Research Abstracts
Vol. 16, EGU2014-8867, 2014
EGU General Assembly 2014
© Author(s) 2014. CC Attribution 3.0 License.
Brittle-ductile deformation and kinematics during exhumation of
metamorphic complexes below detachments: examples from Sifnos and
Syros Islands (Greece)
Giovanni Luca Cardello, Vincent Roche, Valentin Laurent, and Laurent Jolivet
Université d’Orléans, ISTO - Institute of Earth Sciences, Orléans, France ([email protected])
Exhumation of metamorphic core complexes is accompanied by progressive strain localization within large-scale
shear zones, which may evolve into long-lived bounding detachments affected by ductile to brittle deformation.
Despite the well-studied P-T-t patterns of individual nappes, their relative timing, mode and kinematics of exhumation are debated. In this study, in the frame of the Mediterranean syn- and post-orogenic deformation, examples
of shear zone hierarchization and strain localization from Sifnos and Syros islands (Cyclades, Greece) are documented in detail in order to explain 3D-geometries and regional kinematics and are here tentatively related to the
Ar/Ar ages available in literature. During the Eocene syn-orogenic uplift, the degree of strain localization increases
progressively from blue- to green-schists deformation. Some of these shear zones where then reworked during the
Oligo-Miocene post-orogenic deformation in different, usually warmer P-T conditions and a new episode of strain
localisation, and an evolution toward brittle faulting, either along the main detachments or along newly created
faults (as in Sifnos). Such shear zones demonstrate long-lived efficiency, especially where fluid circulation enhance retrograde metamorphic reactions. During Neogene, the final shape and exhumation of domes is the result
of crustal thinning and brittle-ductile deformation in the whole Cycladic region. Although stretching directions
along individual kilometric scale shear zones may be complex in the details, a simple general picture is shown
for the Oligo-Miocene episode, less so for the Eocene one. Most Cycladic islands show a top-to-the-North sense
of ductile shear from the syn-orogenic to the post-orogenic stage, this is the case of Sifnos for instance. The synorogenic stretching is however often more E-W trending, as exemplified by Syros and Tinos. The top-North or
Top-East sense of shear is attributed to the NCDS for the post-orogenic stage and to a syn-orogenic detachment
(Vari D.) for the syn-orogenic stage. However the southwestern Cyclades show clear top-South post-orogenic kinematic indicators related to the WCDS, with a complete ductile to brittle evolution. As for the NCDS the WCDS
leads to intense ductile deformation in its footwall. To the east of Serifos this ductile top-South sense of shear is
lost. Only top-South brittle faults are found in Folegandros and Sifnos where they cut across the older foliation.
The complexity of the distribution of shear sense on Syros and Sifnos, both in the ductile and brittle regimes,
during the post- and syn-orogenic stages, is discussed in the framework of the transition in time from syn-orogenic
exhumation faults to post-orogenic detachments and of the interactions between different sets of detachments, such
as the NCDS and the WCDS.