Magmatism in the Sierras Pampeanas of Córdoba
BONALUMI and Edgardo BALDO
ORDOVICIAN MAGMATISM IN THE SIERRAS PAMPEANAS OF CÓRDOBA. During
the Ordovician period, the Sierras Pampeanas of Córdoba constitute the foreland
of the Famatinian orogenic belt. The gneissic-migmatic basement and granitoids
of lower Cambrian age was deformed by ductile shear zones and intruded by
igneous rocks related to the Famatinian magmatic arc.In the lower to medium
Ordovician period (499-460 Ma) little plutons and dikes of tonalitic,
trondhjemitic, granodioritic, (TTG magmatism) and, to a lesser degree, granitic
composition were emplaced. The plutons are elliptic or round-shaped, they cut
the metamorphic foliations of lower Cambrian age, and, in contact with marbles,
they form high to medium temperature metasomatic skarns. The plutons are mainly
concentrated in the eastern side of the ranges (Sierra Chica, Sierra de Cuniputo
and Sierras de San Marcos) and in this area they are of tonalitic-trondhjemitic
composition with minor granodiorites. In the Sierra de Guasapampa, stocks of
granitic-granodioritic composition of similar age occur. These geographical
distribution suggests a systematic compositional variation of these plutons,
with predominance of the tonalitictrodhjemitic varieties eastwards and
granitic-granodioritic types westwards. In the Sierra Norte of Córdoba,
rhyolite dikes of shallow level of emplacement and little plutons of granitic
composition are recognised; The TTG magmatism of the Ordovician period in Córdoba
is rich in Na2O ( 3.2 – 5.8%), CaO (3.4 – 2.6%), and Sr (800 – 400 ppm),
very depleted in K2O (0.65 – 2.02%), FeOt (0.70 – 1.20%), Cs (0.2 –2.3
ppm), Y (1 – 23 ppm) and U (0.2 – 1.5 ppm). Besides, this magmatism has very
low Rb/Sr ratios (0.015 – 0.12), positive or absent Eu-anomaly (Eu/Eu*= 0.9
– 2.4), [La/Yb]n ratios between 20 and 55, relatively low 87Sr/ 86Sr initial
ratios (0.705 – 0.707) and eNd between + 1.5 and – 4.8. This geochemical
signature suggests at least for some of the trondhjemitic units, a deep magmatic
source and probably astenospheric mantle source.In the regional context, the
Ordovician magmatism of Córdoba represents an inner magmatic arc, emplaced in
the Pampean basement of the western Gondwana margin. This arc developed
contemporaneously with the main Famatinian magmatic arc, located westwards; the
latter gave rise to huge metaluminous “I-type”, metaluminous and calcic
batholitic units that outcrop in the Chepes, Ulapes and Valle Fértil ranges.
EL MAGMATISMO ORDOVÍCICO EN LAS SIERRAS PAMPEANAS DE CÓRDOBA. Durante
el período Ordovícico, las Sierras Pampeanas de Córdoba constituyeron el
antepáis del cinturón orogénico Famatiniano, el basamento gneisico-migmático
de edad Cámbrica inferior fue intruido por rocas ígneas vinculadas al arco
magmático famatiniano y deformado en fajas discretas de cizallamiento dúctil.
En el Ordovícico inferior a medio (499 - 460 Ma) se emplazaron pequeños
unidades plutónicas y diques de composición Tonalítica, Trondhjemítica,
Granodiorítica y minoritariamente Granítica (magmatismo TTG). Los plutones
presentan formas circulares o elípticas en planta, cortan las foliaciones metamórficas
del Cámbrico inferior y generan aureolas metasómaticas de alta temperatura en
contacto con los mármoles. Se concentran mayoritariamente en el sector oriental
de las sierras, (Sierras Chicas, Sierras de Cunuputo y San Marcos ) y en estos
sectores la composición es esencialmente Tonalítica a Trondhjemítica siendo
menos frecuente las granodioritas. En la Sierra Norte de Córdoba se reconocen
diques riolíticos de emplazamientos muy someros y plutones menores de composición
granítica, en tanto que al oeste, en la Sierras de Guasapampa afloran plutones
de composición granítica y granodiorítica de edad similar a los anteriores.
La distribución geográfica sugiere una variación sistemática de la composición
de estos plutones con un incremento de las variedades graníticas - granodioríticas
hacia el oeste y de las variedades trondhjemíticas - tonalíticas al este. El
magmatismo TTG del Ordovícico de Córdoba se caracteriza por ser rico en Na2O (
5,8 - 3,2%), CaO (3,4 - 2,6%) y Sr (800 - 400 ppm ), muy deprimido en K2O (0,65
- 2,02%), FeOt (0,70 - 1,20%), Cs (0,2 -2,3 ppm), Y (1 - 23 ppm ) y U (0,2 - 1,5
ppm). Presentan además muy bajas relaciones de Rb/ Sr (0,015 - 0,12), ausencia
de anomalías negativas de Eu (Eu/Eu*= 0,9 - 2,4), relaciones [La/Yb]n entre
20-55, relaciones iniciales 87Sr/ 86Sr relativamente bajas (0,705 - 0,707) y (Nd
entre +1,5 a - 4,8. Esta signatura geoquímica sugiere, al menos para algunas de
las unidades trondhjemíticas, una fuente magmática profunda y probablemente de
vinculación con el manto astenosférico.
el contexto regional, el magmatismo Ordovícico de las Sierras de Córdoba
representa un arco magmático interno, emplazado sobre el basamento pampeano del
margen occidental de Gondwana, el que se desarrolló contemporáneamente con el
arco magmático principal famatiniano, ubicado mas al oeste, y que dio l ugar a
la formación de las grandes unidades batolíticas de tipo ¨I¨, metaluminosos,
como los aflorantes en las sierras de Chepes - Ulapes y Valle Fértil.
Ordovician magmatism. Córdoba. Argentina
clave: Magmatismo Ordovícico. Córdoba.
Sierras Pampeanas of Córdoba (SPC) has a complex tectonothermic and magmatic
history initiated in the lower Cambrian – Upper Proterozoic, with the
formation of a calc-alkaline magmatic arc, emplaced on continental crust and
followed by a cortical thickening with development of a high grade metamorphism
and anatexis, that formed migmatitic complexes with Cdr + Grt + Sil + Kfs
(minerals symbols after Kretz, 1983) and “S-type” granites of 520 Ma.
(Rapela et al., 1998, Sims et al., 1998 and references therein).
This evolution is assigned to the Pampean Orogenic Cycle proposed by Aceñolaza
and Toselli, (1972) and in the south-east sector is characterized by a short
life ( 25-35 Ma) and fast exhumation of the metamorphic complex (Baldo et al.,
the lower to middle Ordovician period, the Cambrian basement of the SPC has been
the foreland of a new orogenic cycle (Famatinian Orogenic) and the magmatic
activity is manifested in the development of small and isolated plutons,
distributed in the Sierra Chica, Sierra Grande and Sierra Norte (Fig. 1).
Seventeen main plutons are adscript to the famatinian magmatic event, which have
been studied by several authors and with different degree of detail and that are
assigned to the Ordovician magmatism through geochronologic dating or
geochemical correlation. These plutons are generally of reduced dimensions (3 to
10 km of diameter) and its composition is mainly trondhjemitic – granodioritic
for the ones located in the oriental sector of the SPC, granodioritic in the
central sector and granitic – granodioritic in the occidental sector. In the
central and northern sector of the Sierra Chica and in the Sierra of Cuniputo,
swarms of tonalitic dikes are observed, with N-S directions and subvertical dip
(>70°). On the other hand, in the Sierra Norte of Córdoba the plutons and
subvolcanic rocks are of granitic and rhyolitic composition.
main tectonometamorphic event assigned to the Ordovician of Córdoba is the
formation of important milonitic belts in the Green schists facies, with N-S
directions and high grade dip to the east, that represents inverses faults with
top to the west (Martino et al., 1993 a-b, Simpson et al., 2001).
The age of this deformation is not well constrained and the location in the
Ordovician time is on accounts of cut relations with the plutonic events and in
general restricted to the upper Ordovician, which allows primary to correlate it
with the Ocloyic tectonic phase of the Famatinian cycle.
The Tres Arboles shear belt, in the southwestern of Córdoba, is a main milonitic shear zone of SPC and probably represent the principal tectonic contact between Pampean and Famatinian Orogenic Belt (Whitmeyer and Simpson, in press). Recent observations carried on by Fagiano et al. (2002), in the milonitic belt Guacha Corral, state that the dominating planar fabric occur after the thermal peak and is determined by two retrograde associations, one in amphibolites facies (Bt + Sil) and the other
in green schists facies (Chl+ Ms + Ser). These events would have been produced
during the Famatinian Cycle. However, Martino et al., (2002) propose an Upper
Cambrian ages for the milonitic belt of Los Túneles, in the west sector of SPC.
paper is a review and a compilation of the petrographic, geochemical and
geochronological data of the main plutons and dikes assigned to the Ordovician
in the Sierras of Córdoba, and its integration in the regional context is
1. Geological map of the Sierras de Córdoba. Locations
petrographic and geochronological data
Sierra Chica Sector
Güiraldes Trondhjemite: (30°57.5’ LS - 64°27.1’LW). This
pluton is located to the northern sector of Sierra Chica (Fig.1) and it was
described by Perez et al., (1996 a and b), Lyons et al. (1997) and
Rapela et al. (1998). It has a roughly elliptic shape of about 10 km of
length, it is lengthened in NW direction and intruded in a discordant way to the
metamorphic basement, It carry xenoliths of schist, amphibolites and marbles,
producing on the latter an epidotic skarn. It has also microgranular enclaves
with Pl + Qtz + Bt + Ms (tonalitic) and enclaves of dioritic rocks with Pl + Hbl
(>50%). It has a rough foliation, but penetrative, which accentuates towards
the pluton’s margins. Is a semibritlle deformation that produce the
orientation of the muscovite and quartz crystals, which anastomosely surround
the euhedric crystals of plagioclase, the foliation has an average direction of
N 310°/ 65 E.
magmatic texture is granular and is composed by 40-45% of Pl (An 20-25) + 35-40%
Qtz + 10% Ms ± Bt ± Kfs, as accessories Ep, Zr, Ap, Mnz and Chl + Ep2 as Bt
alteration, the color index is < than 8, which allows to be classified as
et al., 1998 obtained for this magmatic unit an age of 499 ± 5Ma (U-Pb
SHRIMP in magmatic zircon), an age of 496 ± 2 Ma (U-Pb traditional in zircon)
and an age of 438 ± 9 Ma (UPb SHRIMP in monazite).The firsts represent a
crystallization ages and is the most ancient registered for this type of
magmatic unit in the SPC. The age of 438 ± 9 Ma in monazite could represent the
postcrystalline deformational event that affected the Güiraldes trondhjemite.
San Agustín Trondhjemite: (31° 58’38’’LS - 64° 23’57’’LW). Located
in the southern sector of the Sierra Chica, it is the minor of a group of
similar bodies of this sector and it is constituted by discontinuous and
elliptic outcroppings with a inner deformation of fragile type, that produces a
very pronounced foliation of NNW direction. It is a white grayish rock, of thick
granular texture and compound by Pl (andesine) + Qtz + Bt + Ms and ± Kfs.
Rapela et al., (1998) characterize it geochemically and define it as a
very characteristic trondhjemite, fact through which the authors infer an
Calmayo Trondhjemite: (32° 01’46’’LS - 64° 27’29’’LW). The
Calmayo pluton, located to the south of the previous body, is one of the most
representative, it presents an approximately circular shape and it has about 3.5
km of diameter. The petrological features were described by Martino and Fagiano
(1982) and Martino et al., (1995). Has been emplaced discordantly in the
metamorfic complex of the southern Sierra Chica, it has altered xenoliths of
mafic rocks, gneisses and marbles, with a metasomatic alteration on the latter.
It is also observed a marked development of fractures produced by an overimposed
brittle deformation event. It is a leucotonalite with >> Pl (An 20) + Qtz
+ Bt ± Ms ± Kfs, as main accessories Ap, Zr and Ep and sericite as subsolid
alteration products. Sinmagmatic aplitic intrusives and variation of the grain
size towards the contacts are distinguished inside the pluton.
Agustín trondhjemite as well as the Calmayo one do not present isotopic dating,
nevertheless the composition and the field relations allow that these are
incorporate in to the magmatic event of Ordovician age.
El Hongo Trondhjemite:
(32° 11’48’’LS - 64° 23’21’’LW). El Hongo pluton is located in the
environs of the locality of Embalse de Rio Tercero. It is emplaced, as well as
the Calmayo pluton, in the Metamorphic Complex of south of Sierra Chica. It
presents a slightly rectangular shape of about 4 km of length and it is oriented
in ENE-WSW direction. It was described by Martino and Fagiano, (1982) and more
recently by D’Eramo et al., (1999).
contacts with the country metamorphic rocks is tectonic and the pluton is
densely cracked, mainly in the oriental sector where the rock presents an
evident cataclastic deformations with development of tectonics breccia.
tonalite presents a light gray color, in part whitish, it has medium to coarse
grain and it is composed by >> Pl (An 21-24) + Qtz + < 10% Bt ± Kfs.
The texture is granular hypidiomorphic with the plagioclase in irregular
crystals and with notably concentric zoned texture. In the central sector of the
pluton, it has a more basic facies with Hb (D’Eramo et al., 1999). The
same authors cited an age of 434 ± 22 Ma (K-Ar in biotite). Considering that
the Bt is a little stable mineral for the K-Ar system and that its closing
temperature is relatively low, it is probable that it does not reflect the age
of crystallization, but the age of cooling or of some other posterior tectonic
event. These biotite K-Ar age is very similar to the monazite age of 438 ± 9 Ma
in the Güiraldes pluton.
In the central part of Sierra Chica and specially along the Quebrada del Río
Suquía, it is possible to observe outcroppings of little tabular bodies that
have variable thickness from only 0.5 m to 40 m as maximum, which form swarms of
parallel dikes. These intrusive were firstly described by Gordillo, (1958) and
Gordillo and Lencinas (1979) and more recently by Toselli (1999).
dikes have a very regular directions almost N-S and subvertical dipping, they
cut with low angle the metamorphic foliation S2 of general directions 320º/60E.
They always present a sharp contact with the country rock, they can show a
chilled margins and angular metamorphic xenoliths are common in the next to the
contact. These dikes are late in correlation with the other intrusive rocks of
the same area, they are only cut by the granitic pegmatites, of probable
affinity with the Achala magmatism (Upper Devonian).
(1958) defined three main types:
45-48 % Pl (An 25-30) + 25-30 % Qtz +15-20 % Bt ± Kfs ± Hbl (Ttn + Ap + Mag +
Zrn). They have a fine to medium granular or porphyritic texture with phenocryst
of euhedric plagioclase and frequently with oscillatory concentric zoning and a
thin external zone of albitization (less than 0.01 mm). The biotite is the only
mafic mineral present and it is generally abundant, with zircon inclusions and
pleochroic halos. This type forms the most wide dikes.
Pl + Qtz + Hbl ± Bt (Ttn +Ap + Ep). This rocks are textural and chemically very
different to the previous ones, they do not have porphyric texture and they are
of fine grain (0.1 to 0.2 mm) and the biotite is substitutes by hornblende.
Compositionally are similar to the previous ones, but they present a well marked
porphyric texture with aphanitic matrix. It has two generations of plagioclase,
one it is a basic oligoclase with concentric zonal structure and that forms
euhedral phenocrysts, and the other, it is of less size and more albitic. The
quartz is totally in the fine matrix. The mafic mineral can be Bt as well as Ho.
Ep, Ap, Py and Ti in less proportion complete the minerology. In general, these
are dikes of small thickness.
Trondhjemitic variety of these dikes is recognizes by Toselli (1999) and it has
light gray color, with granular or porphyric textures with 60% of Pl + 34% Qtz +
6% of Bt ± Ms and Ap, Zr and Op as accessories. They have fluidal textures and
an important postcrystalline deformation.
textural and field evidences suggest a lower emplacement of these intrusives
rocks, which would have emplaced in a relatively could and rigid basement. The
age of the tonalitic dikes is not well known in the Quebrada del Rio Suquia,
nevertheless, On the similar dike of Las Tunas (environs of Cosquín city),
Gromet (com. Pers.) obtained an age U-Pb in zircon of 460 ± 7 Ma (upper
intersection of the concord over three points). If this represents a
crystallization age, these intrusives would represent the closing of the
Famatinean magmatic event in the SPC. The cooling age of 428 ± 12 Ma (40Ar -
39Ar in Bt) for pseudotachylytes in the Rio Suquía sections (Northrup et al.,
1998) probably marc the upper limit for the ductile deformation and for the
emplacement of these intrusives rocks.
Piedra Grande Tonalite:
(31° 05’23’’ LS - 64°31’56’’LW). In the place Alto de la Piedra
Grande, located in the eastern sector of the “El Perchel- Pampa de Olaen block¨,
outcrop intrusives rocks of tonalitic to granodioritic composition, associated
with aplitics and pegmatitics.
Piedra Grande Tonalite is the most representative pluton, it has 1,200 m of
length by 500 m of wide (Pastore, 1932; Gomez, 1983) and it has a NNE-SSW
directions, intrudes in a subconcordant way to La Falda metamorphic complex and
carry xenoliths of this late of centrimetrical sizes. A little marked foliation
is recognized. It is classified as a Tonalite of dark gray color, composed
essentially by Qtz + Pl + Bt and scarce Kfs and Ms, the texture is granular with
fine to medium grain and change to porphyric in the marginal facies with
phenocrysts of plagioclase. Though there are not precise dating of these rocks,
this type of bodies, not very deformed, post metamorphic and of tonalitic
composition, are similar to the bodies of the Ordovician age of the region.
only geochronological information that is disposed of this unit it is an age of
377 ± 15 Ma (K – Ar in Bt, Linares and Gonzalez 1990) and it probably
represents a late deformation stage.
Granitic Pluton of Loma Ancha: The
next of La Calera city, in the Quebrada del Río Suquía, outcrop a little
pluton with aproximately elliptic shape of about 500 m long by 350 m wide and
lengthened in NNO-SSE direction. It intrudes the cordieritic migmatites of La
Calera and the high temperature milonites of La Estanzuela shears belt, it is
affected by a brittle deformation that deforms the quartz crystals and produces
“kink band” micro folds in the muscovite. This granite is intruded by the
tonalitic dikes previously described.
has a granular texture of coarse grain with big flakes of secondary muscovite
(5-7 mm), the modal composition is: 35% Qtz + 21% Kfs + 37% Pl + 5-15% Ms Bt and
Ap, Zr and Grt as accessories (Gordillo, 1958, Toselli, G.1999).
only age of this ganite is a K-Ar age in Ms ( 447 ± 15 Ma, Linares and Gonzalez
1990) and probably it represent the stage of the blastesis of the secondary
muscovite. The granite cut de migmatic fabrics of the cordieritic migmatite with
a metamorphism age of 522 ± 8 Ma (U-Pb in monazite, Rapela et al.,
1998), and is intruded by the tonalitic dikes of 460 Ma for which its age would
be between these two events.
Sierra de Cuniputo - San Marcos and Ascochinga Sector
Cruz del Eje Granodiorite:
This outcropping is a small lightly circular stock of granodioritic composition
which dimensions do not overcome the 200 m of diameter. It outcrops in the
environs of the Cruz del Eje dyke’s wall, its color is white grayish with dark
spots as a consequence of the presence of biotite. It presents a granular
holocrystalline of medium grain texture. Its mineralogy is represented by
lightly zoned plagioclase, microcline, with a great development and poiquilitic
texture, that includes almost all the mineralogy, the quartz presents a light
wavy extintion, but neigther deformation nor pulverization are observed, the
biotite and muscovite complete the mineralogy.
there are no specific geochronological data about this rock, this type of
no-deformed bodies present compositional particularities, geomorphologicaly and
structurally much alike to the ones attributed to the Famatinian magmatic cycle.
La Fronda Trondhjemite: (30°52’03’’LS - 64°38’18’’LW). This
magmatic unit was described by Massabie, (1982), Caffe (1993), Caffe and Baldo,
(1994) and Lyons et al., (1997) and geochemically characterized by Rapela
et al., (1998). It outcrops to the south of the Quilpo quarry and to the
west of Rio Pintos (Fig.1). This is a ovoidal pluton of 6 km of length by 4 km
of wide, it is elongated in the same directions to the foliation of the
metamorphic country rocks and partly interdigitated with this, but its relation
is clearly discordant in the north and south contact. It intrudes gneisses,
schists and amphibolites of the Cruz del Eje-La Falda Metamorphic Complex,
remaining these as xenoliths and pendants inside the pluton. In the North
contact, it intrudes the marbles of the Quilpo Formation, developing skarns of
Grt-Wo. It has a penetrating foliation in the border of the body which
diminishes towards the core, the foliation is given by the orientation of the
secondary muscovite and biotitic schlieren.
is a leucotonalite with granodioritic and granitic facies, has a light gray
color, equigranular texture of coarse grain (2 to 10 mm), formed by 30-40 % Qtz
+ 35-50 % Pl + 2-4 % Kfs + 5-16 % Ms (primary and secondary) + 3-6 % Bt, as
accessories Ap, Zr, Mnz, Op and also Ep secondary, Chl as alteration
first ages for this intrusive body were published by Massabie (1982), who
obtains an age of 455 Ma ± 15 (K-Ar in Bt). More recently, Rapela et al.,
(1998) define a Rb-Sr isochrone of 474 ± 6 Ma (MSWD = 4.3).
In different sectors of the Sierras de Córdoba swarms of pegmatitic that
intrude the metamorphic basement are distinguished. These pegmatites has a
similar features that in the rest of the Sierras Pampeanas. They are very rich
in potassium feldspar and muscovite and they are concentrated in sectors which
seems to indicate a deformational control in its emplacement. In the
Ascochinga-Carape area and in the Sierra de Cunuputo with ages of 435±7 Ma and
447±7 Ma (K-Ar in Ms) were cited and these ones can represent the intrusion or
deformation age (Rapela et al., 1998).
Sierra Norte sector
Located in the northern extreme of the Sierra Norte of Córdoba and south of
Santiago del Estero, they are a subvolcanic dikes that have up to 40 m of thick
and they can reach 5 km of legth (Bonalumi, 1988). In the environs of Oncan, in
Santiago del Estero province, they outcrops as extrusive rhyolitic bodies. They
intrude the granodiorites and granites with Hbl + Bt of the magmatic arc of the
lower Cambrian and they are rocks of pale pink color, of fine to very fine
granulometry with porphyric texture in the hypabyssal bodies to microporphyric
in the rhyolites themselves. The most abundant mineral is the quartz, that is
observed very clean and not pressed (the rock reaches up to 78% of SiO2 in the
most evolving terms), the potassium feldspar and the plagioclase, that is An
(8-10), complete the minerology. The rock can be classified as leucorhyolite,
the only mafic minerals are the scarce laminas of microcrystalline biotite, this
fact is geochemically corroborated, since the FeO values do not overlap the
0.85% on these rocks an age of 494 ± 11 Ma was observed (Rb-Sr Isochrone,
MSWD=2.2, Rapela et al., 1991) locating it in the Lower Ordovician
El Cerro de Tulumba Granite: (30°23’66’’LS - 64°05’44’’LW). In
the austral sector of Sierra
the El Cerro granite neither enclaves or metamorphic xenoliths are observed,
either a postcrystalline deformation is identified, which is very evident in the
other granitic units of the sector, allowing to infer a late emplacement and
genetically unbound of the main magmatic Cambrian event.
composition of the pluton is homogeneous and it is a leucocratic monzogranite,
with granular texture and medium grain size, composed by 34-38% Qtz + 23-34% Pl
(albitic) + 23-30% Kfs (microcline perthitic) + 5-12% Ms and as accessory Ap, Zr
and small garnet crystals. An isochron Rb-Sr suggest an age of 434 ± 39 Ma
(MSWD = 0.2, Baldo et al., 1998), that would locate this granite in the Upper
Villa Albertina Granite: (30°41’33’’LS – 64°17’59’’LW). It
outcrops to the north and to the south of Villa Albertina and it is a N-S
elongated pluton that has up to 8 km of length by an average wide of 2.5 km. It
was described by Gordillo et al., (1997) as a monzogranitic pluton (Qtz + Pl +
Kfs + Ms + Bt), with granular texture an medium grain, which presents scarce
deformation and it intrude the Ischilín mylonitic belt, including xenoliths of
this one. It is important to highlight that the Sierra de Ischilín, where this
granitoid is emplaced, occupies the meridional extreme of the Sierra Norte and
it is essentially constituted by metaluminous granodiorites with Hbl + Bt + Ttn
though there are not absolute ages about this granite, this type of non-deformed
plutons, that cut of ductil shear zone, can be compared with the other
Sierra Grande Sector
Paso del Carmen Tonalite: (31°04’31’’LS – 64°55’01’’LW). In
the north of the Sierra Grande, near to Paso del Carmen locality, it outcrops an
important intrusive defined by Olsacher (1960) as “Paso del Carmen
granodiorite”, and later investigated by Caminos and Cucchi (1990) and Lyons, et
al. (1997). It is a body of lightly triangular shape oriented in E-W
direction, of about 6.5 km of length by 2.5 km of wide. It intrudes discordantly
cutting almost perpendicularly the NNW foliation of the country gneiss, which
does not suffer any type of deviation in the proximities of the contact (Gromet
and Simpson 1998). Internally it does not register foliation by deformation and
it presents an isotropic texture, granular hypidiomorphic of medium to coarse
granulometry. The mineralogic composition is: Qtz + Pl + Bt + Ep + Hbl + Ttn. It
has an important kaolinic and sericitic alteration of the plagioclases and the
chloritization and epidotization of the ferromagnesians minerals.
variations and minor syn-magmatic intrusive dikes are distinguished, specially
in the southeast border of the pluton, where the dikes of porphyric tonalities,
microdiorites of 2- 3 m of wide, and pegmatitic veins are frequent.
and Simpson, (1998) define an U-Pb zircon age of 474±5 Ma (upper interception
of the concordia with MSWD = 1.6) indicating for this non-deformed pluton an
emplacement in the Lower to Middle Ordovician.
Sierra de Guasapampa Sector
Charquina Granodiorite: (30°40’13”LS - 65°53’50’’LW). In
the northwestern border of the SPC, to the west of the La Playa, it outcrops a
pluton of ovoidal shape with its major axis northsouth direction and of about 8
km of length by 3.5 km of wide. The country rocks, are gneisses and migmatites
of the San Carlos Massif in the eastern sector and milonites and gneisses in the
western sector. The pluton cut the milonitic foliation of the Los Túneles shear
zone that has a direction of N 320° / 45° NE (Martino et al., 2002).
and Lira (1998) recognize for this pluton two main facies, the one of lesser
development is a biotitic monzogranite of medium grain, outcropping in the
eastern border and central part of the body, constituted by 36% Qtz + 32% Pl (An
08), 24% Mic. + 7% Ms + <1% Bt, as accessories Ap,Zr, Rt, Grt, Ep and as
alteration Chl, Ms, Ep, Op and carbonates. The facies that occupy the greater
part of the pluton is a biotitic muscovitic granodiorite of uniform medium grain
(1 to 2 mm). The mineralogical composition is: 35% Qtz + 36% Pl (An 17) + 12%
Mic + 8% Bt + 4% Ms, besides of Ap, Ep and Zr as accessories and Chl, Ep2, Ms
and Ttn as alteration. It also presents numerous syn-magmatic apilitic and
pegmatitic intrusions N-S and E-W oriented.
et al., (2002) report an age of crystallization of 478 ± 8 Ma for the
granodioritic facies of the pluton La Playa (age U-Pb zircon SHRIMP) confirming
the age Rb-Sr obtained by Rapela et al., (1998).
Cuesta de los Romeros Tonalite: (31°04’35’’LS - 65°18’07’’LW).
This intrusive body is
emplaced inside the San Carlos metamorphic-anatectic massif, more precisely in
the western side of the Sierra del Coro (Bonalumi, et al. in press). It is an
intrusive of tonalitic composition lightly elongated with NW direction and it
has 6 km of length and 2.5 km of wide. The tonalite is of gray color with black
spots of biotitic composition with granular xenomorphic texture. The primary
mineralogy is represented by: Qtz-Pl-Bt-Ti-Ap-Zr-Ep1. A strong sericitation of
the plagioclases is observed, while the chloritization of the ferromagnesian is
incipient. The Ep2 is a secondary replaces of Pl, Bt and Ti. The pluton present
a marked deformation of their primary mineralogy, the Qtz show strain shadows,
the Bt has “kink” folds and the Pl has an incipient deformation.
(1989), makes a detailed description of its emplacement and observes a
concordant position with a deformation cycle of NNW-SSE direction, with
gradational passages to the country rock, which are as well cut by pegmatites
bound with the Mesa del Coro granite (see the next), those same pegmatites cut
the tonalite, so Fernandez (1989) suggests an older age for the Cuesta de Los
Romeros tonalite, in regards to Mesa del Coro granite (471 ± 58 Ma using K/Ar
in Bt), for which it could be located in the Famatinian cycle.
Mesa del Coro Granite:
(31°05’12.2’’LS - 65°17’44’’LW) this granite outcrops 2 km south
of the locality of Cienaga del Coro and very near to the eastern extreme of the
Cuesta de Los Romeros tonalite. Its main outcropping (Fernandez, 1989) is
lengthen with NNW-SSE bearing, direction in which it has 2 km by a variable wide
between 0.9 km in the south half and 0.5 km in the north. The contacts are
generally pure. It is a rock of pink color with light gray tonalites, it
presents a midium granulometry being its main mineral components: Qtz + Kfs + Pl
+ Ms + Bt(scarce), while the accessories that integrate it are: Grt, Crd, Ap,
Zrn, Tur, Toz, Fl, which is indicating its strong peraluminous tendency and an
interesting grade of specialization. Locally and near the pegmatites important
Tur crystals. It is important to highlight that in some localized sectors (on
calc-silicatic rocks) it has been produced a thermic metamorphism with hornfels
formation. Petrographically it is a muscovite granite with hydrothermal
overimpossed alteration. Geochemically it is located inside the peraluminous
subalkaline granites. This type of body is considered an specialized granite,
with abnormal values in W and Sn (average 10 ppm and 29 ppm respectively: n=11).
It was dated in 471 ± 58 Ma., using K/Ar in biotites, (Fernandez, 1989).
main feature of the Ordovician magmatism of the SPC is the association of
trondhjemitetonalite- granodiorite, (TTG magmatism of Rapela et al.,
1998) which develops preferably in the Sierra Chica, Sierra de Cuniputo – San
Marcos and some isolated plutons in the north of Sierra Grande and Sierra de
Guasapampa (Fig.2). The only granitic pluton in the Sierra Chica could be the
Loma Ancha granite, which has been tentatively included together with the others
TTG magmatism is of slight to moderately peraluminous tendency and enriched in
Na2O, with values upper than 3% and in some cases close to 6% (Fig.3), it is
also rich in CaO and Sr, specially in the tonalitics and trondhjemitics
varieties and comparatively depleted in K2O (0.65 – 2.02%), FeOt, Cs (0.2 –
2.3 ppm) and other incompatible elements, being also specially low the relations
Rb/Sr and the total Rare Earths contents (Fig.3).
et al., (1998) and Pankhurst et al., 2000 also indicate, for the
TTG group, a positive or absent Eu-anomaly, relations [La/Yb]n of 2 –55,
initial 87Sr/ 86Sr ratios relatively low (0.705 – 0.707) and values of the eNd
between + 1.5 a – 4.8. these features are specially evident in the
trondhjemitic units as the ones from Güiraldes and San Agustin, suggesting, at
least for these ones, a deep and basic magmatic source probably of astenospheric
the Sierra Norte of Córdoba some notable differences in regards to the rest of
the SPC are observed. The rhyolitic intrusives are varieties of high silica
(> 75% of SiO2) moderately peraluminous, rich in K2O (4.5 - 5.8% K2O) and
high relations of Rb/Sr (Fig.3). they have a strong negative Eu-anomaly (Table
1) and high initial relations of 87Sr / 86Sr (0.80 – 0.89 ), which suggests an
important cortical participation in its genesis. (Rapela et al.,
Cerro Granite shows some geochemical similitudes with the rhyolitic porphyry,
specially its high tenor in SiO2 (75 to 77%), its low peraluminosity, relatively
high relations Rb/Sr (> 40) and a strong negative Eu-anomaly (Table 1).
However, the relation [La/Y]n of 12-26, and eNd of –1.9 would be evidences of
a more deep source for this granite (Baldo et al., 1998).
magmatism of lower to middle Ordovician age of the SPC is characterized mainly
by the generation of small plutons, tabular dikes and subvolcanic
manifestations. These ones have discordantly emplaced in the Lower Cambrian
metamorphic or igneous basement, cutting the metamorphic foliations and carry
small and angular xenoliths or blocks than these ones, they can also generate a
metasomatism effect in contact with marbles and calc-schists. They never show a
high temperature ductile milonitization and the only postmagmatic deformation
that they register is of semi-fragile to fragile type. From this it is deduced
that its emplacement has been at relatively low deep and in a previous rigid
basement. The tabular dikes has porphyric texture and an aphanitic matrix, which
also indicates a shallow emplacement.
to the nowadays available geocronological information (see plutons’
description), the trondhjemites are the most ancient units, with a maximun age
of 499 ± 5 Ma (Güiraldes trondhjemite), they are followed by the granodioritic
units with ages of 474 – 478 Ma (La Fronda, La Playa and Paso del Carmen) and
finally, the tonalitic dikes ( 460 ± 6 Ma).
distribution of the different plutons, (Fig. 1) suggest same compositional
control for the emplacement of this plutons, the trondhjemite + tonalite ±
granodiorites plutons (TTG group) are located preferable to the east of the SPC,
while the granodioritic and granitic are located to the west.
Ordovician magmatism of the Sierra Norte de Córdoba has a similar aspect with
respect to the levels of emplacement, but show important geochemical differences
that suggest a greater cortical participation in the genesis of these ones.
In the context of Sierras Pampeanas, the Ordovician magmatic event of the SPC is coeval with the early “I” type metaluminous and calcic suite magmatism, located farther west and that forms a big batholitic unites of granodiorites with Hbl + Bt, these are representatives of the main subductions magmatic arc of the Famatinean Orogen (Pankhurst et al., 2000). In this context the TTG of the SPC would represent an inner magmatic arc, emplaced on the pampean foreland of the western margin of Gondwana.
F. Miller, H. and Toselli, A. 1990. El ciclo pampeano en el noroeste argentino.
Universidad Nacional de Tucumán. Serie Correlación Geológica. 4. Tucumán.
E., Pankhurst, R., Rapela, C., Saavedra, and Mazieri, C. 1998. Granito “El
Cerro”, Magmatismo colisional famatiniano en el sector austral de la Sierra
Norte-Ambargasta, Córdoba. 10º Congreso Latinoamericano de Geología y 6º
Congreso Nacional de Geología Económica. 2: 374-378. Buenos Aires.
E., Saavedra, J., Rapela, C., Pankhurst, R., Casquet, C. and Galindo, C. 1999. Síntesis
geocronológica de la evolución paleozoica inferior del borde sur de Gondwana
en las Sierras Pampeanas, Argentina. Acta Geológica Hispana. V32. Nº
1-2. p.17-28. Madrid. España.
F. 1979. Trondhjemite:
Definition, environment and hypotheses of origin. In: Barker, F. (ed). Trondhjemites,
dacites and related rocks. pp. 1-12. Elsevier. Ámsterdam
A.A. 1988. Caracteristicas Petrologicas y Petroquimicas de los Granitoides
Asociados a la Mineralización de Manganeso En el Norte de la Provincia de Córdoba
y Sur de Santiago del Estero. República Argentina. V Congreso Geológico
Chileno. Tomo II E 47 - E 61. 1988. Santiago. Chile.
A., Martino, R., Sfragulla, J., Baldo, E., Zarco, J. Carignano, C., Tauber, A.,
Kramer, P., Escayola, M., Cabanillas, A., Juri, E. and Torres, B. (in press).
Memoria de la Hoja Geológica 3166-IV Villa Dolores. SEGEMAR.
Bs. As. Aregntina
A., Sfragulla, J., Pérez, D., Rubio, M. , Guereschi, A.., López A.. and
Gozalvez, M. 2001. Cuarzo en la Provincia de Córdoba. Su Calidad Química.
VII Congreso Argentino de Geología Económica. Tomo 2 . 89-95. Salta
2001. ISBN.987-98990-1.4. Salta. Argentina
P. 1993. Petrología y estructura del área comprendida entre las localidades
de Pintos y Quilpo Sur, Departamento Punilla y Cruz del Eje. Provincia de Córdoba.
Trabajo Final. Inédito. 229 páginas. Córdoba. Argentina.
P. and Baldo, E. 1994. El plutón trondhjemitico La Fronda. Borde
Occidental de la Sierra de Cuniputo. Córdoba. Argentina. VII Congreso Geológico
Chileno. V II. 972-976. Concepción. Chile.
R., and Cucchi, R., 1990. Levantamiento geológico estructural de la región
situada entre Villa de Soto y La Candelaria. Córdoba. Informe Inédito.
Subsecretaría de Minería de la Nación. 41 pp. Buenos aires. Argentina.
F., Llambías, E. and Pinotti, L. 1999. Geología, Petrografía y Edad del plutón
El Hongo. Sierra Chica de Córdoba. XIV Congreso Geológico. I – 93-94.
M., Pinotti, L., Esparza, M. and Martino, R. 2002. Faja de cizalla Guacha
Corral. Sierras Pampeanas de Córdoba, Argentina. 15º Congreso Geológico
Argentino. CD, Art. 320.
6 pags. El Calafate. Argentina.
R., 1989. Geología y Metalogénesis del Distrito La Bismutina, Sierra de
Guasapampa. Provincia de Córdoba. Tesis Doctoral. Museo de La Plata, Nº
532: 51-94. La Plata. Argentina.
M., 1983.¨Estudio Geológico Económico del yacimiento de Tonalita Piedra
Grande. Departamento Punilla, Pedanía San Antonio, Provincia de Córdoba. Trabajo
Final. Departamento Geología Básica, Facultad de Ciencias Exactas, Físicas y
Naturales. Universiodad Nacional de Córdoba. (Inédito). 50 pp. Córdoba.
M., 1998. Geología de los stocks graníticos de Serrezuela y La Playa y
metalogénesis de sus mineralizaciones asociadas. Sierras de Serrezuela y
Guasapampa. Tesis Doctoral Inédita. Facultad de Ciencias Exactas Fisicas y
Naturales. Universidad Nacional de Córdoba. Córdoba. Argentina.
M. and Lira, R. 1998. Geología y aspectos del plutón granítico de La Playa ,
Sierra de Guasapampa. Provincia de Córdoba. Revista de la Asociacion
Geologica Argrgentina 53 (3): 291-305. Buenos Aires. Argentina.
C.E., 1958. Estudio químico-petrográfico de las rocas intrusivas de la
quebrada del Río Primero. Bol. Acad. Nac. Cs., Córdoba, 40: 141-170. Córdoba.
D., Kirschbaum, A. and Baldo, E. 1997. Magmatismo del Borde Oriental de las
Sierras pampeanas: Los granitoides de la Sierra de Ischilín, Provincia de Córdoba.
Argentina. 8º Congreso Geológico Chileno. 2: 1290-1294. Antofagasta.
Chile Gordillo, C. 1984, Migmatitas cordieríticas de las Sierras de Córdoba;
condiciones físicas de la migmatización. Miscelánea 68: 1-40, Academia
Nacional de Ciencias. Córdoba. Argentina.
C. and Lencinas, A., 1979, Sierras Pampeanas de Córdoba y San Luis. En Turner,
J.C. (De.): Segundo Simposio de Geología Regional Argentina, Academia
Nacional de Ciencias, Vol. I., 2: 577-650. Córdoba. Argentina.
D., Kirschbaum and Baldo, E. 1997. Magmatismo del borde oriental de las Sierras
Pampeanas: Los Granitoides de la sierra de Ischilín. Provincia de Córdoba.
Argentina. VIII Congreso Geológico Chileno Vol II . 1290- 1294. Antofagasta.
P. and Simpson, C. 1999. Age of the Paso del Carmen Plutón and implications for
the duration of the Pampean Orogeny. Sierra de Cordoba, Argentina. 8º
Congreso Geológico Argentino I-149-151. Salta. Argentina.
R., 1983. Symbols for rock -
forming minerals. Am. Mineral. 68:277-279. Lawrence. USA.
E. and González, R., 1990. Catálogo de edades radimétricas de la República
Argentina 1957-1987. Publicación Especial de la Asociación Geológica
Argentina, Serie B Nº 19: 214-229. Buenos Aires. Argentina.
P. and Stuart-Smith, P., 1997. Geology of the “Sierras Septentrionales
de Córdoba”. 1:250.000
map sheet. 1- 67. Geoscientific Mapping of the Sierras Pampeanas.
Argentine-Australian Cooperative Proyect. Australian Geological Survey
Organisation. Subsecretaría de Minería de la Nación. Buenos
R., 1988. Geología y petrología del basamento metamórfico de la región
situada al norte de Cuchilla
Sierra Grande de Córdoba. Tesis Doctoral, Universidad Nacional de Córdoba. 174
pp. (Inédita). Córdoba. Argentina.
R.D. and Fagiano, M. 1982. Los intrusivos menores de la Sierra Chica Sur de Córdoba.
Trabajo Final. Departamento Geología Básica. Facultad de Ciencias Exactas, Físicas
y Naturales. Universidad Nacional de Córdoba; Córdoba (Inédito). 78 pág. Córdoba.
R., Law, R. and Simpson, C., 1993a. Evidence for orthogonal contractional
orogeny in The Pampean Ranges of Córdoba, Central Argentina. EOS 74 (16):
302. Baltimore. USA.
R. Law, R. and Simpson, C., 1993b. Taconic-(Ocloyic)-aged west - directed
ductile thust in basement rocks of The Sierras Pampeanas Argentinas. GSA.
Abstracts with Programs. 25,6, A 233. Boston. USA.
R., Kraemer, P., Escayola, M., Giambastiani, M. and Arnosio,M., 1995. Transecta
de las Sierras Pampeanas de Córdoba a los 32ºLS. Revista de la Asociación
Geológica Argentina, 50(1-4): 60-77. Buenos Aires. Argentina.
R., Guereschi, A. and Sfragulla, J., 2002. Deformación frágil y relaciones
regionales de la faja de deformación Los Túneles en la sierra de Pocho y
Guasapampa. Córdoba, Argentina. 15º Congreso Geológico Argentino. CD,
Art. 293. 6 pags. El Calafate. Argentina.
A. 1982. Geología de los alrededores de Capilla del Monte y San Marcos.
Provincia de Córdoba. Revista de la Asociación Geológica Argentina XXXVII.
Nº 2 153-173. Buenos Aires Argentina.
C. and Baldo E. 1994. Facies graníticas de los alrededores de Tulumba,
Sector Sur de la Sierra Norte de Córdoba. Argentina. VII Congreso Geológico
Chileno. Vol II. 1115-1119. Concepción. Chile.
C., Simpson, C. and Gromet, P. 1998. Early Paleozoic history of the Eastern
Sierras Pampeanas , Argentina. Development of a Cambrian arc and accretionary
prism along the margin of Gondwana. Actas del X Congreso
Latinoamericano de Geología y VI Congreso Nacional de Geología Económica. Vol
II. 400-403. Buenos Aires. Argentina.
J., 1960. Descripción geológica de la Hoja 20h - Los Gigantes, Provincia de Córdoba.
Dirección Nacional de Minería y Geología, Anales XII. Vol. 90: 5-46
Buenos Aires. Argentina.
J., 1972. Descripción geológica de la Hoja 21h, Cerro Champaquí, Provincia de
Córdoba. Boletín Dirección Nacional de Geología y Minería. 133:
1-64. Buenos Aires. Argentina.
R., Rapela, C. and Fanning, H. 2000. Age and origin of coeval TTG, I-and S-Type
granites in the Famatinian belt of NW Argentina. Transactions of Royal
Society of Edinburgh: Earth Sciences. 91. 151-168. Edinburgh.
F., 1932. Hoja 20i -Córdoba- del Mapa Geológico de la Argentina, región
oriental y media de la Sierra de Córdoba. Dirección Nacional de Geología y
Minería. Boletín 36: 1-67. Buenos Aires. Argentina.
M.B., Rapela, C.W. and Baldo, E.G., 1996a. Geología de los granitoides del
sector septentrional de la Sierra Chica de Córdoba. XIII Congreso Geológico
Argentino y III Congreso de Exploración de Hidrocarburos, Actas V: 493-505.
Buenos Aires. Argentina.
M. B., Baldo, E. G., Saieg, A. and Domínguez, J. 1996 b. Tipología de epidotos
en granitoides de la Sierra Chica septentrional de Córdoba, Argentina. Revista
del Instituto de Geología y Minería. Vol. 11 Nº 1, : 71-91. Jujuy.
C. W. Pankhurst, R and Bonalumi, A. 1991. Edad geoquímica del pórfido granítico
de Oncán. Sierra Norte de Córdoba. Sierras Pampeana. Argentina. 6º
Congreso Geológico Chileno. 1:19-22.
C. and Pankhurst, R., 1996. Cambian plutonism of The Sierras de Córdoba: Pre
Famatinian subduction? And crustal melting. XIII Congreso Geológico
Argentino y III Congreso de Explotación de Hidrocarburos. V: 491. Buenos
C. W., R. J. Pankhurst, J. Dahlquist and C. M. Fanning, 1999. U-Pb shrimp ages
of Famatinian granites: New constraints on the timing, origin and tectonic
setting of I- and S- Type magmas in an ensialic arc. 2º Simposio
Sudamericano de Geología Isotópica, 264-267. Carlos Paz. Argentina.
C. W. Pankhurst, R., Casquet, C., Baldo, E., Saavedra, J., Galindo,C., and
Fanning, C. 1998. The Pampean orogeny of the soutern PROTO-Andes: Cambrian
continental collision in the Sierras de Córdoba. In:
R and Rapela, C. (eds). The Proto-Andean Margin of Gondwana. Geological
Society, Special Publications, 142, 181-217. London.
C. ,Whitemeyer, S., Depaor D., Gromet, P., Miro, R., Krol, M. and Short, H.
2001. Sequential ductile to brittle reactivation of major fault zones along the
accretionary margin of gondwana in Central Argentina.
Holdsworth, R, Strachan, R., Magloughlin, J. y Knipe, R. (eds) 2001. The Nature
and Tectonic Significance of Fault Zone Weakening. Geological Society.
Special Publications. 186. 233-255. London.
J. Ireland, T., Camacho, A. Lyons, P., Pieters, P., Skirrow, R., Stuart-Smith, P
and Miró R. 1998. U-Pb, Th-Pb y ar-Ar geochronology from the southern Sierras
Pampeanas, Argentina: Implications for the Paleozoic tectonic evolution of the
western Gondwana margin. The Proto-Andean Margin of Gondwana. Geological
Society, Special Publications, 259-282. London.
A., 1875. Comunicaciones sobre la geología y mineralogía de la República
Argentina. Actas Academia Nacional de Ciencias de Córdoba, Tomo I. Córdoba.
P., Miró, R., Pieters, P., Lyons, j., Sims, P. and Camacho, A., 1996. Estructura
tectónica de las Sierras Pampeanas Australes. Argentina. AGSO-
BOX 378 -4 pp. Camberra
G. 1999. Magmatismo ácido calcoalcalino en la zona de La Calera. Sierra Chica
de Córdoba. Consideracio
15 de Octubre de 2002
Aceptado: 12 de Diciembre de 2002
INICIO Curso 2004 Cátedra Geología Argentina Orógenos Famatinianos Ultima modificación: 28 de septiembre de 2005