Gondwana Research, I.! 5, No. 2, pp. 325-337.
02002 International Association for Gondwana Research, Japan
ISSN: 1342-93ix
Common Crustal Source for Contrasting Peraluminous Facies
in the Early Paleozoic Capillitas Batholith, NW Argentina
J.N. Rossil, A.J. Tosellil, J. Saavedra2,A.N. Sia13,E. Pellitero2and V.P. Ferreira3
INSUGEO, Universidad Nacional lie 7ucurnaii, Tuctiman, 4q00, Argentina
lnst. de Recursos Naturales y Agrobiologia, Universidad de Salamanca, Salarnanca, Spain
NEG-LABISE, Department of Geology, UFI'E, C.P. 7852, Recife, PE, 50732-970,Brazil
(Manuscript received May 15, 2001; accepted October 8, 2001)
Abstract
The Ordovician Capillitas batholith, part of the northern Pampean ranges, NW Argentina, exhibits two peraluminous
granitic facies in its eastern portion: (a) coarse- to medium-grained, porphyritic mafic facies with biotite, cordierite and
aluminosilicates, carrying sillimanite-, cordierite-, and andalusite-bearing migmatitic enclaves and schlieren and (b)
enclave free, mica poor, coarse-grained, porphyritic felsic facies, with andalusite and sillimanite. Banded hornfels aureoles
contain cordierite poikiloblasts, biotite, plagioclase and quartz. The low-P mineral assemblage in these granites, enclaves
and restites, suggests partial fusion of a supracrustal protolith. The two facies plot as two separate groups in geochemical
variation diagrams, suggesting that they evolved from different magma batches derived from the same source, rather
than from in situ fractional crystallization. The composition of felsic facies granites corresponds to pelite and
metagraywacke-derived melts, whereas cordierite-bearing mafic granites follow a trend indicating mixing of pelitederived melts and corresponding restites. The mafic-facies granites approach more the continental crust composition
than the felsic-facies ones, which display more pronounced Ba and Sr negative anomalies. The average ( L a m ) , -11
rules out a high pressure garnet-rich source and the low normalized Sr contents, in both granitic facies, suggest a
recycled metasedimentary protolith. Absence of mafic intrusives that could have assimilated pelitic schists, allow us to
infer that melting took place at rather low T and under high water activity. Heat to trigger partial fusion could have been
radiogenically generated and stored in the upper crust during deformation and thickening of the continental crust, with
further release during decompression. The Capillitas batholith, emplaced close to an I, S-type granite boundary line in
this region appears to be an Argentinean analogue of the Cooma Series supersuite in the Lachlan Fold Belt, emplaced
close to the eastern Australian I, S-type granite boundary line.
Key words: Cordierite, mafic and felsic facies, Paleozoic, common source, peraluminous.
Introduction
The strongly peraluminous Capillitas batholith, north
of Andalgala town, in the Pampean ranges of NW
Argentina, is one of the best examples of cordierite-bearing
granitoids in southern South America. In this region, early
Paleozoic magmatic epidote- and cordierite-bearing
granitoids were emplaced in distinct geographic areas (Fig.
1). Some of the cordierite-bearing granitoids resemble
equivalent plutons of the Lachlan Fold Belt in Australia
in several respects and among them, the Capillitas
batholith deserves special attention for its large size (1,600
km2 ) and excellent exposures. This work focuses on the
petrology and geochemistry of the eastern portion of this
batholith with a particular emphasis on the two granitic
facies (porphyritic biotite and cordierite-rich monzonitic
to granodioritic facies, and an equigranular, felsic
cordierite-poor nionzogranitic facies), both carrying
andalusite and sillimanite (Fig. 2).
For a long time, the genesis of strongly peraluminous
granitoids has attracted the attention of petrologists, since
it has been demonstrated that granitic melts from which
aluminum silicates can crystallize, could be experimentally
produced (Green, 1976;Clemens and Wall, 1981;Thompson,
1982; Miller, 1985). The problem with the petrogenesis
of these rocks does not reside only in producing
peraluminous melt but also in its protolith. White and
Chappell (1977) advocated the incorporation of restitic
material into melt of pelites, and Elburg (1996) proposed
that the interaction of mafic magmas with continental
crustal rocks could explain the particular composition of
the S-type granites.
J.N. ROSS1 El'At..
326
68'00'
64'00'
66'00'
IIS boundaryline
l8
0
/%
-\
7
?
'
''
South Anierica
cd'
Tucumun
Capillitas batholith
- 1 - iI
'
\c\
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Pampean
Ranges
(11
I- 1 -
N
A
-
0
50
100km
Epidste-bearing granitoids
Cardierite-bearing granitoids
0
San Juan
nu' cordierite-bearing
Pig. I. Siinpiificd geological map of NW Argentina indicating locations of early Paleozoic cordierite.-bearing granitoitis and magmatic epidorebearing granitoids. Locations of possible I, S-type granite boundary lines are shown.
A1t 11 o ugh muscovite - and cord i e rite -bear i n g
pcraluminous graiiitoids can occur in the same area and
have identical ages, they generally do not represent
members of the same differentiation trend (Barbarin,
1996). Patifio Douce (1995, 1999) has experimentally
demonstrated that fusion of muscovite schist can generate
leucocratic melts through muscovite dehydration melt,
but these differ from S-type melts because the latter have
much higher MgO, FeO, TiO, and CaO and lower SiO,
than the leucogranites. He proposed that mafic magma
(50%) and continental crust rocks could interact at low
pressure (5.S kb) in a process by means of which melt
compositions seem to match those of natural S-type
compositions.
In the present work it is suggested, based on geological
relationships, rniiieral composition, textures, nature of
enclaves in the granites, as well as geochemical data, that
the granitic magmas under consideration resulted from
partial fusion of continental crustal rocks, at low pressure
( 1 5 kb), without a visible contribution of a mafic magma.
'This work also provides petrological and geochemical
information on a representative S-type granitoid of NW
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Gondwana Research, V. 5, No. 2,2002
EARLY PALEOZOIC CAPIL,LITASBATHOLITH, NW ARGENTINA
327
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Tertiary sediments and volcanic rocks
Felsic granitic facies
Mafic cordierite-bearing monzogranitic facies (Capillitas pluton)
Other porphyritic granites and granophyres
Schists and grieisses
Faults
Contacts
ig. 2. Geological i m p of part of the Capillitas batholith area, in NW Argentina.
Argentina for comparison with similar S -type granitoids
of the Lachlan Fold Belt (e.g., Cooma supersuite) in a
Paleozoic Gondwana reconstruction.
Previous Work
The first complete petrographic and geological
descriptions of the Sierra de Capillitas granitoid rocks were
provided by Gonzalez Bonorino (1950a, 1951a, b) who
undertook a detailed petrographic-structural work in the
Gowdwana Reseavch, V. 5,No. 2,2002
Aconquija range and surrounding areas. Acefiolaza et al.
(1982) mapped the geologic and structural lineaments
in the region north of Andalgala. Indri (1979, 1986) and
Toselli and Indri (1984) reported, for the first time, the
presence of cordierite and aluminum silicates as accessory
phases in this batholith, providing descriptions of the main
geological and petrographic features of the Cuesta de
Capillitas and its basement.They also distinguished an
equigranular and a porphyritic facies.Toselli et al. (1996)
carried out a petrographic and geochemical research on
328
J.N ROSS1 L.T A1 ,.
the two granitic facies and concluded that crustal
inetasedimentary rocks were probably the source for the
peraluminous magmas.
Geochronological woik perforrned by McNuti et al.
(1975) provided a Rb--Sr age of 413 Ma (Sro= 0.7146),
while I<-Ar ages on biotite and muscovite range between
365 and 471 Ma (Caelles et al., 1971; Linares and
Gonzalez, 1990). Rapela et al.(1999) obtained a U-Pb
SHRIMP age of 470t3 Ma on a porphyritic biotite-rich
moiizogranite. These age data suggebt that the granitic
magmatism in this area took place from the Ordovician
to the late Silu-rian,assuring that the Capillitas batholith
was emplaced during the Famatinian magmatic cycle
(Aceiiolaza and Toselli, 1973).
coiintry rocks imcierweirt low to medium grade regioiial
metaniorphisin, ds shown by muscovite.chlorite quartz
and miiscovite-biotite-cordieriteassociations. The granitic
intrusion developed hornfels aureoles, a static regime that
generated cordierite and biotite porphyroblasts in the
phyllites and schists of appropriate chemical composition.
The intrusion mechanism has been attributed by Gonzalez
Bonorino (1950b) to a major stoping and a passive, lateto post-tectonic, emplacement. In fact, only minor
defonnation is observed.
The batholith is foliated at the margins, where biotiterich schlieren and enclaves of biotite-sillimaniteandalusite-cordierite rocks and biotite-sillimanite flow
bands are commori.The contact relationships with phyllites
and schists are sharp and subconcordant.
General Geology
According to Gonzilet Bonorino (195Oa, 19SOb) and
Aceiiolaza et al. (1982), the Capillitas batolitli extends
from the Aconquija range to beyond the Quebrada de
B e l h to the west, forming a huge granitic area. With a
surface of about 1,600 kin2, the Capillitas batholith
encompasses the southwestern portion of the Aconquija,
Capillitas, Santa Barbara ranges, Bola del Atajo Hill arid,
to the west, it continues to the Ovejeria range and to the
region to the south of it (Fig. 2). This huge granitic area
is inteirupted by gravity faults (roof pendants of the
metamophic country rock) of which the most
representative ones are: Negro Hill, Quebrada de Villavil,
and Quebrada de Amanao. Granite outcrops are often
partially covered by conglomerates and Cenozoic alluvial
cones.The current configuration of the blocks of the ranges
resulted from the Cenozoic Andean tectonics that fractured
the blocks with reverse faults. Jordan and Allmendinger
(1986) estimated a general offset of 2,000 to 8,000m for
fractures of the Pampean ranges in general, while the
net shortening has been of about 2% only. Gonzalez
Bonorino (1950a) estimated that the vertical displacement
for the Capillitas range block was about 4,000 ni. This
differential vertical movement of blocks has transported
deep sections of the Capillitas batholith upwards, exposing
zones where the interaction of granitic magma with
material of migmatite-like or restitic rocks is very intense,
especially in the Capillitas range.
In the study area, granites are not associated with
migmatites, but migmatites crop out in the eastern and
northwestern regions of the neighbouring Sierra de
Aconquija (not shown in Fig. 2) and have been described
by Gonzdlez Bonorino (1951a).
Gonzalez Bonorino (1950a, 1951a, 1951b) found the
Capillitas batholith to be a late- to post-tectonic, epizonal
intrusion in phyllites and schists of the basement. These
Petrography
111 the western portion of the batholith, two granitic
facies have been identified: (a) a mafic facies very rich in
cordierite and biotite that predominates in the Capillitas
range-Sarita Barbara area, cropping out along the hillside
to the west of the Negro Hill and including a major N-S
structure known as the Amanao-Visvis fault and (b) a felsic
mica-poor facies, with representative outcrops in the
Quebrada del Potrero, Toma de Agua de Andalgala and
Quebrada de Villavil (Fig. 2) .The felsic granitic facies
corresponds to the porphyritic facies N,and equigranular
facies V of Gonzalez Bonorino (1951a), and the mafic
granitic facies to the porphyritic facies VI. The modal
composition for these rocks is found in table 1, where
divergences between the two granitic facies are clearly
seen: felsic granites have 90%, on average, of feldspars
quartz and lo%, on average, of micas (biotite +
muscovite), being muscovite > biotite; while the mafic
facies shows 65% in average of feldspars quartz and
3504 in average, of biotite muscovite cordierite, with
biotite > muscovite. The felsic facies granites constitute
minor domains in the Capillitas batholith, and the contact
between the two granitic facies, according to Gonzalez
Bonorino (195 la), is transitional.
Mafic, biotite-rich, porphyritic rriorizogranite fornis the
largest outcrops of the batholith. Lens-shaped xenoliths
of country rocks (schists, minor calc-silicates and
hornblende schists) are restricted to the marginal zones
of the mafic porphyritic monzogranites and may be several
meters long.
Dark metasediinentary lens-shaped enclaves up to few
decimeter-long of biotite migmatite-gneiss are abundant
throughout the batholith. They contain dark, niediumgrained iiielanosomes with biotite, andalusite, cordierite
and sillimanite. Enclaves with magmatic textures are rare
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Gondwana Research, V. 5,No. 2,2002
EARLY PALEOZOIC: CAPILLITAS RATHOLITFI, NW ARGENTINA
329
Table 1. Modal mineralogy of the felsic and mafic granitic facies and enclaves of the Capillitas batholith.
m
zU
ii
4
cr,
m
E?
V
s
2
E
Sample
K-feldspar
Plagioclase
Quartz
Biotite
Muscovite
Cordierite
1824a
1824b
1825
1972
2124
2747
2748
2387
2388
2396
39.9
39.7
11.9
25.1
32.6
29.5
18.7
16.3
13.4
35.4
19.5
20.6
28.6
37.3
29.0
31.1
28.2
17.3
25.2
19.9
36.3
31.1
42.0
26.1
32.6
28.9
39.5
56.6
51.3
33.3
1.2
0.9
0.0
6.0
3.7
2.3
5.7
2.7
0.5
2.3
2.7
7.0
17.4
3.8
1.0
7.9
7.6
6.7
9.3
8.4
0.0
0.0
0.0
0.0
0.1
0.0
0.0
0.0
0.0
0.0
1596
5837
5833
5834
5839
1269
1271
1273
653a
17.1
16.3
15.2
7.8
21.3
10.4
22.4
6.7
3.7
13.7
16.4
20.2
31.9
16.5
18.1
25.2
18.9
34.9
22.2
29.6
27.8
26.9
27.3
35.7
30.3
33.9
29.0
23.8
23.2
23.0
19.3
28.3
19.4
13.1
23.6
21.0
15.2
4.9
5.1
5.1
2.8
2.9
1.9
5.4
9.0
7.0
8.1
6.0
5.8
2.9
13.2
6.3
10.8
2.0
653b
2427
7.5
0.0
17.8
0.0
37.0
31.1
22.4
39.9
2123
1262
0.0
0.0
45.3
30.1
28.8
25.1
17.4
23.5
6.9
2.5
0.2
2.7
3.5
7.8
7.5
20.3
3.3
1.7.5
to absent, but aplitic to pegmatitic narlow dykes are rather
common.
Mafic, porphyritic, two-mica monzogranites are gray
to pink, with coarse-grained groundmass, containing
andalusite, sillimanite, cordierite, biotite, muscovite,
tourmaline, zircon and apatite. Microcline megacrysts up
to 15 cm long occupy 15% to 50% of the volume of the
rock. Perthitic microcline is found as megacrysts and in
the groundmass and exhibits inclusions of euhedral
plagioclase, rounded quartz and biotite. In the
equigranular facies, microcline is commonly anhedral with
cross-hatch twinning. Microcline megacrysts are earlycrystallized phases as already pointed out by Gonz6lez
Bonorino (1950a). Plagioclase (An,,) i s variably zoned,
only rarely showing patchy zoning, where resorbed
oligoclase core is surrounded by albite. Fresh and welldeveloped biotite showing zircon and monazite inclusions
forms large flakes and, sometimes, is altered to chlorite
magnetite. Cordierite constitutes a common accessory
phase usually found as very corroded anhedral grains,
surrounded by micaceous material, and presenting biotite,
quartz, muscovite and zircon inclusions. Quartz grains
with fibrolite and isolated fibrolite are also common
inclusions, while green spinel is rare. Sometimes,
cordierite is altered to pinite and white mica.
Sillimanite is commonly observed in two-mica
monzogranites as felted masses of fibers of fibrolite or
developed from biotite, that also includes quartz,
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Gonduma Research,
5,No. 2,2002
Sill/andalusite
Apatite
'Tourmaline
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.4
0.5
0.0
1.4
0.5
0.0
0.0
0.0
0.0
0.3
0.0
0.0
0.0
0.1
0.2
0.0
0.0
0.0
0.4
0.7
2.3
0.5
0.2
0.0
0.3
0.5
0.0
0.5
0.3
0.4
0.4
0.2
0.1
0.0
0.2
0.0
0.0
0.1
0.2
0.6
0.0
0.3
0.2
18.2
0.0
2.4
0.0
0.0
0.1
0.1
0.2
2.2
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
plagioclase, muscovite and cordierite. It is sometimes
found as contorted fibrous aggregates associated with
biotite that is also sigmoidally deformed. This form is
observed surrounding plagioclase, quartz and K-feldspar
grains, suggesting that these minerals pushed their borders
against fibrolite aggregates during their growth.These
textures are hardly believed to be magmatic ones.
The felsic, porphyritic, and equigranular monzogranite
is white to reddish, medium-to coarse-grained, with
muscovite and biotite. The fine-grained, almost aplitic
muscovite-rich facies carries abundant tourmaline. Quartz
is found in the groundmass or as sub-rounded inclusions
in biotite and cordierite. Plagioclase (albite-oligoclase,
An > 10) is usually unzoned, and occurs as albite-carlsbad
twinned hypidiomorphic laths. Andalusite is generally
found as anhedral to subhedral grains or prismatic with
visible cleavage, pink to colorless weak pleochroism,
sometimes exhibiting patchy zoning. It usually occurs as
relicts within muscovite flakes that represent its alteration
product. As in the case of coexisting cordierite, andalusite
may not be of magmatic origin, but may be partially
derived from fibrolite-andalusite-cordierite-bearing
enclaves. Enclaves of such a composition probably
originated in deep-seated rocks (migmatiticmelanosomes)
or they are restites, since this is a virtually absent
assemblage in the sorrounding metamorphic country
rocks. Black tourmaline is found as interstitial, isolated,
subhedral crystals.
J.N. ROSS1 ET AL.
330
The mafic and felsic monzogranites, when with
cordierite, andalusite and sillimanite, show unusual
symplectitic intergrowths that include biotite, muscovite,
quartz, microcline, plagioclase, cordierite and sillimanite.
Besides myrmekite, muscovite appears to replace Kfeldspar giving rise to muscovite-quartz symplectitic
textures. Andalusite and cordierite are also replaced by
muscovite. Quartz-biotite symplectites, close to the
margins of some biotite grains, are common. Symplectitic
textures, grown in subsolidus state, can be explained by
the replacement reactions:
1 ) Cordierite + K-feldspar
H,O + biotite
sillimanite + quartz + andalusite
2) Sillimanite 4- K-feldspar H,O + muscovite +
quartz
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Xenoliths and Encl aves
Xenoliths are lens-shaped, usually centimeter to
decimeter long, restricted to the marginal zones of the
batholith and many of them are clearly derived from the
wall rocks. Most show fine, equigranular hornfels-like
textures. Those derived from psamopelitic rocks are
composed of quartz-biotite-plagioclase and rare potash
feldspar and muscovite. Fine-grained cordierite is present
in small amount.
Calc-silicate xenoliths are very fine-grained showing
plagioclase, epidote and garnet. Hornfelsic xenoliths with
hornblende, biotite, plagioclase and quartz are less
abundant. All of them show sharp contacts and no
assimilation effect with their host granitic rocks.
Enclaves have an appearance of melanosome of
migmatites, are intermediate- to coarse-grained,
foliated,very rich in biotite and have very rare muscovite.
They are often found as lenses several decimeter long
and also with disaggregate aspect forming schlieren bands
in the cordierite granites. Two compositional types are
recognized in these enclaves: (a) melanosomes with
biotite, plagioclase, quartz, andalusite, sillimanite,
cordierite, without potassic feldspar and melanosome with
biotite, quartz, andalusite, sillimanite, cordierite lacking
both potassic feldspar and plagioclase. In any case, garnet
or any higher pressure-assemblage or indication of higher
metamorphic grade has not been observed.
The microgranular enclaves, of unclear origin, are
tonalitic in composition, with igneous texture, usually
rounded, fine- to intermediate-grained, up to few
decimeter long. They are less abundant than the
metasedimentary enclaves.
The Capillitas batholith resembles, in several
respects, the Cooma granodiorite in the Lachlan Fold Belt
of Australia. As in the Capillitas batholith, the Cooma
granodiorite is massive, medium- to coarse-grained and
rich in biotite and cordierite crystals up to 10 cm across,
according to Chappell et al. (1991). The inclusions in this
pluton are all of sedimentary derivation, most are biotiterich and some are rich in sillimanite. They are considered
to be residual material from partial melting (restite). The
most distinctive chemical features of the Cooma pluton
are the very low CaO (average 3.3%) and Na,O (average
2.2%) contents. Similar chemical behavior is observed in
the mafic facies of the Capillitas batholith. Likewise, the
modal abundances of biotite (about 20%), andalusite
(2.5%), and muscovite (4%) observed in the Cooma
pluton are similar to abundances of these phases in the
mafic facies of the Capillitas batholith. The Cooma pluton
is situated near the S/I line boundary in Australia and
the Capillitas batholith, next to the eastern border of the
central zone batholiths that perhaps represent a S, I-type
granite boundary line in Argentina (cordierite-bearing/
epidote-bearing granitoids; Sial et al., 1999).
Geochemistry
Major, trace and rare-earth element (REE) analyses of
33 representative samples of the felsic, mafic granitoids
and enclaves are found, respectively, in tables 2, 3 and 4.
The mafic cordierite granites have average S O ,
contents of 66.45% and the felsic ones, 73.8%. The CaO,
MgO, Fe,O,, and TiO, contents are higher in the cordieritic
mafic granitoids with CaO = 1.21% and MgO Fe,O,,
TiO,= 6.36 %, while the felsic granites have CaO = 0.59%
and MgO Fe,O,t
TiO,= 1.85 %. These diferences in
the major element oxides can be easily observed in the
elemental variation diagrams, that show a distinct
behavior of the two granite facies (Figs. 3a, b) and in the
alumina saturation index (AS1 = 1.3 and 1.2, respectively)
that show a higher perahminosity of the mafic cordieritic
granitoids. This range of composition is similar to that of
other peraluminous cordieritic granitoids in the Pampean
ranges (Rapela et al., 1997, 1998). These oxide variations
are also similar to those reported for S-type, cordieritebearing granites in the Lachlan Fold Belt, Australia (e.g.,
Cooma supersuite, Chappell et al., 1991).
Trace elements like Zr, Sr, Ba and Rb also show these
differences in both granites, with higher Zr, Sr and Ba
contents in the mafic granites and higher Rb contents in
the felsic ones (Figs. 3c,d,e and f). The average REE
content is higher in the mafic granites (162 ppm), while
in the felsic ones the average is 50 ppm.
In the Debon and Le Fort (1983) diagram (Fig. 4a),
the typology of the peraluminous granites is well defined,
where the felsic granitoids lie in the field of muscoviterich leucogranites (field I) while the mafic ones lie in the
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Gondwana Research, V. 5,No. 2,2002
331
EARLY PALEOZOIC CAPIJ,LITAS RATIIOTITH, NW ARGENTINA
Table 2. Major and trace element analyses of the felsir facies of the Capillitasbatholith. ACNK = rnolarAl,OJ(CaO+Na,O+K,O);
n.d.= not determined.
FELSIC FACIES
Sample
1824
1825
2124
2387
2388
2396
2398
2747
2748
6600
6601
6606
6607
6608
6602
SiO,
TiO,
K,O
P,O,
LO1
75.10
0.10
13.20
2.04
0.08
0.08
0.44
2.40
5.60
0.20
0.39
75.10
0.09
13.70
1.94
0.12
0.07
0.46
3.80
3.30
0.36
0.60
72.70
0.13
14.60
2.20
0.09
0.22
0.66
3.20
4.90
0.29
0.37
73.50
0.10
14.70
1.56
0.07
0.1 2
0.47
3.60
4.50
0.32
0.51
73.60
0.10
14.50
1.68
0.49
0.09
0.49
3.80
4.40
0.35
0.60
72.70
0.13
14.40
2.09
0.06
0.16
0.55
3.00
5.40
0.32
0.58
73.80
0.10
14.20
1.84
0.07
0.06
0.49
2.90
5.40
0.31
0.45
71.80
0.18
15.00
1.72
0.07
0.25
0.63
3.40
5.00
0.44
0.88
72.20
0.19
14.80
2.02
0.09
0.22
0.57
3.40
4.80
0.39
0.76
75.42
0.18
12.52
1.67
0.03
0.22
0.80
2.58
5.15
0.22
0.77
73.28
0.08
14.53
0.84
0.07
0.16
0.50
4.01
4:86
0.41
0.82
76.29
0.31
12.12
2.38
0.08
0.71
0.82
2.77
3.51
0.69
1.13
74.74
0.14
13.75
1.13
0.05
0.24
0.56
3.42
4.57
0.43
1.09
72.96
0.17
15.37
1.38
0.05
0.34
0.71
3.63
3.52
0.57
1.55
73.81
0.09
14.16
1.00
0.04
0.16
0.47
3.90
4.09
0.38
0.99
Total
99.63
99.54
99.36
99.45 100.10
1.284
1.239
1.260
1.216
99.37
1.233
1.250
99.56
1.109
334
33
29
20
3
20
5
81
15
6
3
546
140
34
30
1
34
4
52
1
4
4
361
32
92
42
4
25
2
7 03
19
3
3
478
47
77
44
2
25
3
69
1
2
1
471
63
63
41
1
24
5
68
6
3
2
343
32
3 21
43
3
17
1
96
25
4
4
384
12
104
39
2
19
6
89
16
4
3
482
91
167
49
1
21
4
110
2
9
2
384
36
130
49
3
20
2
115
1
10
1
336
20.3
121
39
6.29
20.7
4.3
123
33
20.1
4.8
99.57 100.81 100.12 100.25
1.136 1.229 1.185 1.386
305
419
528
397
35.7
61.5
137
90.1
54
72
78
79
21
23
29
44
7.18
5.81
9.22
10.9
28.4
20.3
20.9
24
2.7
3.6
1.4
4.6
100
120
133
37
14
30
9
7
13.5
9.48
3.56
18.7
6.29
5.89
6.03
3.29
99.09
1.219
99.62
1.232
99.44
ACNK
99.39
1.221
7.81
20.5
n.d.
9.78
1.73
0.15
1.17
n.d.
1.29
0.22
0.43
n.d.
0.3
0.04
4
10.47
n.d.
4.57
0.8
0.1
0.7
n.d.
0.61
0.11
0.27
n.d.
0.27
0.04
12.13
32.2
n.d.
14.77
2.53
0.28
2.33
n.d.
2.36
0.41
0.91
n.d.
0.7
0.09
5.7
15.76
n.d.
8.07
1.39
0.19
1.29
n.d.
1.51
0.28
0.72
n.d.
0.68
0.1 1
5.07
14
n.d.
6.73
1.15
0.13
0.94
n.d.
0.85
0.15
0.35
n.d
0.32
0.05
11.33
30.79
n.d.
14.68
2.56
0.31
2.36
n.d.
3.07
0.57
1.29
n.d.
1.24
0.17
6.45
17.25
n.d.
8.36
1.56
0.17
1.41
n.d.
1.51
0.27
0.65
n.d.
0.5
0.06
12.54
34.66
n.d.
16.56
3.48
0.33
2.31
n.d.
1.22
0.2
0.42
n.d.
0.29
0.06
14.99
45.32
n.d
20.69
3.69
0.37
2.83
n.d.
1.43
0.24
0.48
n.d.
0.3
0.06
27
60.1
6.77
24.4
6.1
0.58
5.68
1.19
6.75
1.22
3.14
0.39
1.83
0.19
20.4
48.7
5.67
21.1
5.37
0.40
4.2
0.66
2.93
0.45
1.11
0.15
0.82
0.08
5.27
12.1
1.4
5.24
1.51
0.17
1.33
0.26
1.5
0.29
0.92
0.17
1.13
0.16
'4120,
Fe20,t
MnO
MgO
CaO
Na,O
Rb
cs
Ba
Sr
Ta
Nb
Hf
Zr
Y
Th
u
La
cc
Pr
Nd
Sm
Eu
Gd
Tb
DY
HO
Er
Tm
Yb
Lu
field for biotite-rich leucogranites (field 11). The felsic
granites show, in general, a variable depletion of REE, a
characteristic common to the most fractionated granites
that show a marked positive correlation between Rb/Ce
and Rb (Fig. 4b), The high Rb/Sr = 11 and Rb/Ba = 4.7
suggest, but are not proof of an evolution through
fractional crystallization, once the possibility of different
pulses of melt from a similar source cannot be ruled out.
In the A-B diagram of figure 5 (Debon and Le Fort, 1983;
modified byvillaseca et al., 1998), samples from the felsic,
cordierite-free, granitoids lie in the F-P field which is
reserved for the felsic peraluminous granites, while
samples from the mafic, cordierite-bearing granites tend
to follow mostly the trend defined by highly peraluminous
granitoids of the Cooma supersuite, Australia, or the
Gondwana Research, V. 5, No. 2,2002
5.3
11.7
1.37
5.29
1.39
0.25
1.22
0.22
1.23
0.24
0.75
0.13
0.88
0.13
28.2
67.6
7.88
29.5
7.45
0.56
5.76
0.85
3.78
0.56
1.31
0.17
0.88
0.09
14.4
33.1
3.77
14.3
3.66
0.31
2.75
0.4
1.77
0.27
0.69
0.1
0.55
0.06
1.209
515
84.9
36
18
11.4
26.5
1.6
37
9
4.07
3.15
Hercynian Layos granite, Spain (respectively Go and Ly
trends in the H-P field of Fig. 5).
Higher REE concentration is observed in the mafic
granitoids due, among other factors, t o a high
concentration of accessory phases like zircon, monazite
and apatite. In both types, a pronounced negative Eu
anomaly can indicate an important feldspar fractionation
at the residue of partial melting in the source or a chemical
characteristic of the source itself (Fig. 6a). For both
granites, the average (La/%),=
11 is interpreted as the
absence of garnet at the source. This characteristic is very
common to many strongly peraluminous granites in the
Pampean ranges (Rapela et al., 1996).
The continental crust-normalized REE patterns for the
mafic granites and enclaves show very similar patterns
332
J.N. ROSS1 ET AL.
Table 3. Major and trace element analyses of the mafic facics of the Capillitas batholith. ACNK= molar Al,O,/(CaO+Na,O+K,O);
n.d. = not
MAFIC FACIES
1270
1273
5832
5835
5837
5838
5841
6593
6594
6597
6598
6605a
6605b
65.50
0.67
14.90
4.82
0.14
2.00
1.70
2.20
4.70
0.52
1.63
66.64
0.54
15.21
4.08
0.08
1.83
1.07
2.60
4.61
0.23
1.47
65.13
0.64
15.22
4.98
0.10
2.20
0.95
2.27
4.32
0.20
1.97
64.51
0.67
15.86
5.30
0.11
2.44
1.22
2.46
3.95
0.20
1.48
66.21
0.66
14.88
4.76
0.09
2.05
1.36
2.39
4.27
0.29
1.40
70.14
0.36
14.23
2.58
0.06
0.98
0.83
2.23
5.75
0.19
1.07
71.55
0.40
14.50
3.14
0.06
1.09
0.59
1.92
5.80
0.14
1.19
69.00
0.54
15.04
4.54
0.1
1.56
1.02
2.11
4.17
0.22
1.74
69.99
0.42
14.77
3.31
K,O
PZO,
LO1
67.20
0.49
14.80
4.00
0.08
1.60
1.90
2.40
4.10
0.56
1.68
1.07
1.18
2.48
5.02
0.24
1.78
66.88
0.67
15.64
5.61
0.1
2.11
1.42
2.41
4.12
0.30
1.09
66.31
0.59
15.34
5.13
0.10
1.68
1.21
2.38
4.30
0.29
1.41
67.95
0.64
14.94
5.28
0.10
1.70
1.21
2.25
4.47
0.32
1.37
Total
98.81
98.78
98.36
98.36
98.42
100.38
100.04
100.34
100.15
98.74
100.23
1.248
1.261
1.335
97.98
1.502
98.20
ACNK
1.505
1.349
1.248
1.380
1.526
1.264
1.418
1.422
1.390
173
10
319
142
4
15
7
204
38
12
1
198
10
373
102
21
6
220
35
9
2
198
9.3
473
107
2.9
10.2
5.3
172
34
12.6
2.71
193
7.8
391
87
2.7
11.7
6.1
191
33
14.20
2.99
222
11.9
362
87
3.8
13.2
5.9
7 89
32
14
3.56
189
8.4
387
93
2.7
12.1
6.4
211
34
14.1
2.65
198
6.1
354
87
2.4
8
4.6
136
30
12.6
2.64
216
8.3
326
82
7.29
14
4.4
112
28
14.8
3.23
231
19.40
357
108
6.81
16.60
6
166
30
13.3
5.81
236
20.2
293
80
6.88
14.5
3.9
109
21
10.2
3.4
182
10.1
308
93
4.55
16
6.2
187
38
13.1
3.32
217
12.8
338
88
3.46
18.6
5.9
I99
42
16.2
2.85
209
12
340
84
3.39
18.4
6.6
225
42.2
19.1
3.34
36.56
87.58
n.d.
39.23
5.17
0.84
3.64
n.d.
2.18
0.37
0.72
n.d.
0.49
0.07
34.81
92.09
n.d.
46.44
6.81
1.04
5.51
n.d.
4.06
0.69
1.28
n.d.
0.78
0.11
33.8
67.3
7.4
28.1
5.71
1.11
5.14
0.91
5.31
1.09
3.4
0.51
3.17
0.46
36.5
74.2
8.17
30.1
6.18
1.13
5.48
0.95
5.7
1.18
3.56
0.52
3.25
0.48
38.3
76.8
8.52
31.8
6.22
1.11
5.5
0.97
5.5
1.12
3.39
0.49
3.09
0.46
37.8
76.7
8.49
32
6.58
1.16
5.98
1.05
6.08
1.2
3.51
0.48
3.0
0.45
28.4
56.9
6.2
23.5
5.3
1.12
4.96
0.91
5.25
1.04
3.13
0.46
3.17
0.47
36.6
77.1
8.31
30.5
6.67
1.22
5.66
1.0
5.46
1.08
3.29
0.53
3.28
0.47
39.8
83.4
9.1
34.7
7.44
1.32
6.1 1
1.09
6.12
1.2
3.51
0.53
3.21
0.44
30.6
63.6
7.02
26.7
5.89
1.03
4.78
0.84
4.64
0.87
2.55
0.39
2.48
0.33
39.6
84.9
9.4
35.4
7.77
1.37
6.66
1.26
7.48
1.51
4.44
0.65
3.91
0.58
42.2
89.2
10.1
37.2
8.31
1.19
7.5
1.37
7.78
1.51
4.35
0.64
3.84
0.51
47.5
101
11.3
43.2
9.62
1.24
8.31
1.51
8.32
1.56
4.33
0.65
3.73
0.49
Sample
SiO,
TiO,
A403
Fe,O,t
MnO
MgO
CaO
Na,O
Rb
cs
Ba
Sr
Ta
Nb
Hf
Zr
Y
Th
IJ
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
DY
Ho
Er
Tm
Yb
Lu
~
2
~
~
~
~
~
~
and remarkable superposition among them, with a more
REE-enriched restitic enclave showing more pronounced
Eu anomaly (Fig. 6b). Multi-element patterns normalized
to the continental crust are also similar, enriched in
relation to the continental crust, with Ba and Nb troughs
approaching the corresponding continental crust values,
and an important Sr trough indicative of a weathered
source (Fig. 6c).
To compare the compositions of both granitic facies to
those of melts experimentally produced by partial fusion
of pelites (e.g., Vilzeuf and Holloway, 1988; Patiiio Douce
and Johnston, 1991 and Patiiio Douce, 1999), we have
plotted (Fig. 7) the percentage of CaO/(Fe,O,, + MgO +
TiO,) against CaO + Fe,03t MgO TiO,, as well as the
molar alumina saturation index (Al,O,/CaO+ Na,O
+
+
0.08
+
+
+
+
K,O) against A1,03
CaO Na,O
K20. The data for
the felsic granitic facies lie in the field for melts obtained
from the partial fusion of muscovite schists overlapped
with that for graywackes, while the mafic granitic facies
data lie near the restite-melt R mixing line in a pelitic
system without the contribution of a basaltic component
melt (Figs. 7a and b).
Discussion and Conclusions
The conditions for generation of a granitic magma from
a H,O-undersaturated mafic pelite (biotite metapelite)
under low pressure (<5 kb) are produced by dehydration
fusion of biotite. The experimental data indicate that, at
minimum temperatures of fusion around 80Oo-85O0C, the
Gondwana Research, V. 5, No. 2,2002
333
EARLY PALEOZOIC CAPILLITAS BATHOLITH, NW ARGENTINA
'Table 4. Major a n d trace e l e m e n t analyses of representative
enclaves of t h e Capillitas batholith. ACNK = molar
AI,O,/(CaO+Na,O+K,O); n.d. = not determined.
ENCLAVE6603
52.73
0.97
21.47
8.54
0.17
3.74
1.68
2.69
4.75
0.22
2.67
0
~
Sample
SiO,
TiO,
K,O
P A
LO1
2427
53.04
1.16
26.44
8.71
0.15
3.29
0.41
0.23
4.68
0.26
2.05
6599
60.10
0.90
18.34
7.51
0.15
4.22
1.70
2.48
3.26
0.17
1.35
Total
100.42
100.18
ACNK
4.277
1.712
Rb
cs
Ba
Sr
Ta
Nb
Hf
Zr
Y
Th
U
354
50.8
93
13
10.5
37.6
8.2
226
57
25.3
13.4
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
82.9
177
19.6
70.7
14.7
2.09
12.3
2.05
11.5
2.28
6.68
1.02
6.3
0.84
A1203
Fe,O,t
MnO
MgO
CaO
Na,O
DY
Ho
Er
Tm
Yb
Lu
6604
65.09
0.88
15.69
5.78
0.05
2.37
0.41
1.29
4.85
0.16
2.05
6609
67.24
0.54
15.18
4.60
0.10
1.80
0.52
2.37
4.63
0.28
1.90
99.64
97.62
99.17
1.698
1.929
1.538
250
16.3
220
115
3.91
16.9
4.6
132
34
14.6
3.54
211
42
262
76
2.67
22.4
7
235
43
20.6
4.04
322
39.1
334
73
3.06
20.2
8.4
285
41
19
4.96
445
101
410
39
4.45
21
4
141
22
11.5
3.50
44.2
91
10.4
39.7
8.2
1.43
7.15
1.18
6.66
1.38
4.09
0.61
3.55
0.5
65.9
139
14.9
54.7
10.9
1.95
8.82
1.51
8.58
1.76
5.14
0.78
4.72
0.68
56.8
117
7 2.8
48
9.63
1.18
7.79
1.33
7.52
1.56
4.8
0.74
4.32
0.61
32.6
69.1
7.48
28
5.86
0.97
4.73
0.79
4.37
0.87
2.62
0.39
2.33
0.34
melt composition remains within limits specified by
percentages and ratios of major and trace elements:
Na,O <3.5%, CaO< 1.2 YO,K,O > 5.0%, Rb/Sr>2.6,
Sr/Ba<0.4, Rb/Ba>0.25, and the contents of MgO and
FeOt in the melt have the following limits: 0.2 to 0.9%
MgO and 1.3 to 3.1% FeOt (Miller, 1985; Williamson et
al., 1997).
The felsic facies granites have an average content of
Na,O of 3.3%, CaO of 0.6%, K,O of 5%, Fe,O,t of 1.5%,
MgO of 0.2%, Rb/Sr = 11, Sr/Ba = 0.4, Rb/Ba = 4.7,
'within the considered range and could be regarded as
pure, or well-fractionated, crustal melts. The high Rb/Sr
and Rb/Ba ratios suggest an independent evolution of
these granites by fractional crystallization. On the other
Gondwana Rfsenrch, I/: 5,No. 2,2002
60
80
70
SiO,
SiO,
SiO,
0 0
8O 8
t
01
60
I
I
70
I
I
80
100
u
70
SiO,
I v mafic cordierite aranites
0
60
SiO,
o felsic granites
0 enclaves
I
Fig. 3. Major element and selected trace element (Zr, Ba, Sr and Rb)
variation diagrams for the mafic cordierite granites (triangles),
felsic granites (circles) and some enclaves (squares).
hand, rare-earth elements decrease while Rb increases,
with fractionation of the granitic magma.
The cordierite granites exhibit average Na,O (2.3%),
CaO (1.2%), K,O (4.6%), Fe,O,t: (4.0), MgO (1.7%),
Rb/Sr (2.2), Sr/Ba (0.3), Rb/Ba (0.6), all of them in the
range for pelitic melts, except for the MgO and Fe,O,t
contents, outside the limits for pure crustal melts. In the
Lachlan Fold Belt, the distinctive features of the Cooma
granodiorite are the very low CaO and Na,O contents
(similar to the Capillitas mafic facies), which have been
regarded as an indication of the rock being derived from
a clay-rich sedimentary source (Chappell et al., 1991).
The experimental data (Patiiio Douce, 1995, 1999)
demonstrate that granites of this particular composition
do not reflect pure crustal melts by the limited solubility
of Mg and Fe and this author proposed a 50% contribution
of a basaltic magma to produce a hybrid magma of this
composition and crystallization products. However, for
the Capillitas batholith, there are petrographical,
334
J.N. ROSS1 ET AL.
150
6o
v mafic cordierite granites
0
50 -
n
(b)
felsic granites
0
8
c\I
0
0
40 -
+
rn
z
+ o
0
0
Y
W
0
I
20
T
II
Q
10
-1 50
0
100
200
Llo
"
200
0
00
300
B = (Fe + Mg + Ti)
h
m
150
0
c\1
+
io
z
s100
+
$
a
50
0
50
100
150
B = (Fe+Mg+Ti)
Fig. 5 A-B diagram (modified from Debon and Le Fort, 1983) for
different series: Central Spain Hercynian Belt (Layos granite,
Barber0 and Villaseca, 1992), Lachlan Fold Belt series: Co
(Cooma series; Chappell et al., 1991), other granites: To
(Tourem, Holtz and Barbey, 1991), TS (Trois Seigneurs;
Wickham, 1987); this work (symbols as in Fig. 2). Fields are:
H-P (highly peraluminous), M-P (moderately peraluminous),
I-P (low peraluminous) and F-P (felsic peraluminous). I/S stands
for the I, S-type granite boundary line.
500
600
Rb
Fig. 4. (a) Diagram A-B from Debon and LcFort (1983). A = A1 - (K + Na + 2Ca) and B = Mg + Fc
(b) Rb/Ce versus Rb diagram for felsic granites. Fields 1 to VI are from Debon and Lefort (op. cit).
200
400
+ Ti for the mafic and felsic granites,
geochemical and geological evidence that this was not
the case: (1) the interaction between mafic magma and
metamorphic rocks of the upper crust to produce a hybrid
S-type magma as that in Capillitas, requires that a large
volume of mafic magma ascended and has been emplaced
in the upper crust. There is no evidence for the existence
of a mafic magma in the area of outcrop of the granitic
pluton (over 1,600 km2); (2) enclaves in the cordieritic
granite are metamorphic in the majority (metapelites to
metapsammites) in which we can distinguish well those
that were derived from the wall rocks, while the biotiterich ones with sillimanite, andalusite, quartz and cordierite
represent restites of incomplete unmixing or melanosomes
of migmatites incorporated, assimilated and partially
disaggregated in the granitic magma; ( 3 )the geochemistry
of these enclaves is in favor of a restitic composition, for
they are enriched in REE, MgO, Fe,O,t and TiO,; (4) when
the oxide contents are plotted in appropriate diagrams of
experimentally-obtained melts, the compositions of
cordieritic granites and their enclaves lie on or very close
to the pelitic melt-restite mixing line (Patiiio Douce, 1999),
while the felsic granites lie in the field of pure crustal
melts.
The necessary temperature for the fusion and formation
of large volumes of granitic magmas could have resulted
from radiogenic heat stored during crustal deformation
and thickening by K, Rb, Th and U, as proposed by England
and Thompson (1984). Gerdes et al. (2000) proposed a
Condwana Research, V. 5, No. 2,2002
EARLY PALEOZOIC CAPILLITAS BATHOLITH, NW ARGENTINA
335
'1
-
/
\
I
La
j
Ba
0.01
I
Ta
U
I
Rb Th
I
I
I
Ce
I
Nb La
I
Zr
Nd
I
Sr
I
I
Hf
I
I
I
I
I
Eu
Pr
I
I
Tb
Ho
I
Tm
Lu
maficfacies
Tb Tm La
1
I
Sm
Y
I
I
I
Yb
Fig. 6. (a) Continental crust-normalized REE patterns for the mafic cordierite-bearing ahd felsic granites (normalizing factors from Taylor and
McLennan, 1985). (b) Continental crust-normalized REE patterns for the mafic cordierite granites and their enclaves. (c) Continental crust
normalized multielemental diagram for the mafic cordierite granites and their enclaves.
model for the batholith of South Bohemia in the Variscan
orogen in Europe, in which they demonstrated the
feasibility of crustal heat production by radioactive
element decay during and after crustal thickening, enough
to explain the thermal evolution with time and crustal
melt volumes. The lack of a study in Argentina that has
quantified crustal deformation and thickening during the
early Paleozoic in the Pampean ranges, as well as limited
isotopic data available for this area, preclude us from
exploring this possibility.
Alternatively, mafic plutonism underplating could have
supplied the necessary heat to trigger melting of
Gondwana Reseauch, V. 5,No. 2,2002
metapelites in the crust in a similar fashion to what
happened in the Lachlan Fold Belt. This is a hypothesis
that deserves consideration in future work.
Acknowledgments
We want to express our gratitude to the National
University of Tucuman, Argentina, and to the National
Council for Scientific and Technological Research
(CONICET) for financial support. Costs of this research
were also defrayed by grants from CIUNT G-120 and
G-127, from the National Agency for Scientific and
J.N. ROSS1 ET AL
336
1.7
Mafic cordisrite granites
Felsic granites
1.6
H 9,
G
y 1.4
(2
5
%
1.3
2
'1.1
ON
3
1.o
0
5
10
15
CaO+Fe,O,+MgO+TiO,
0.8
0.2
0.3
0.4
AI,O,+CaO+Na,O+K,O (Molar)
Fig. 7. (a) CaO over ferromagncsian oxide components versus CaO i ferromagnesian components, in percentage. HP and 1.P thick solid lines
represent, respectively, high and low pressure hybrid pelite-basalt melis. The dashed line R reprpsents melt-restite mixing in a pelitic system.
(b) Molar alumina saturation versus Al,O,+CaO and alkalies. Symbol.; and fields as in figure. 4a (after PatiAo Douce, 1999).
Technological Promotion arid the Secretary of Science and
Technology (project n 7-0-671). We also want to thank
Nubia S. Chaves, Rielva S. Nascimento arid Roberta G.
Brasilino for the assistance with preparation of figures.
This is the NEG-LABISE contribution n. 184.
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