The Western Basement Complex of the Sierra de San Luis underwent a complex deformational and metamorphic history of presumed Proterozoic age. The Phyllite Group and equivalents consist of a thick clastic sequence, whose time of deposition is compared with that of the Late Precambrian-Early Cambrian Puncoviscana Formation. This is intruded by early Famatinian magmatic arc tonalites to granodiorites, whereas an eastern basement unit was affected by early Famatinian mafic/ultramafic intrusions, metamorphism, and deformation. This Early Ordovician plutonism is related to east-directed subduction beneath the western margin of the Pampean terrane. Subsequent compression, plutonism, and variable-grade metamorphism are considered to be Mid- to Late Ordovician in age. Post-Famatinian c. WNW-ESE contraction under greenschist facies conditions led to folding of the cover sediments and uplift of different metamorphic units along mylonite zones which record an oblique sinistral component in the western part of the sierra. Based on a few radiometric data, this stage is interpreted as Devonian in age. It is possible that the compressive event was the result of the collision with the Precordillera (Cuyania) terrane in the west: oblique kinematic displacements, together with some evidence from outside the Sierra de San Luis, can be interpreted as the effect of the indenting terrane.

The Sierra de San Luis consists of Lower Palaeozoic igneous and metamorphic rocks. The granitoids were emplaced between Late Cambrian and Early Carboniferous times, and the most important metamorphic and deformational events occurred during this period. Older metamorphic events have also been recognized but they are poorly constrained. The most important group of granitoids are as follows: (1) Deformed tonalites and granites. The tonalites have a calc-alkaline signature with low La/Yb ratio. They are the Early Famatinian, pre-orogenic, granitoids of Late Cambrian to Early Ordovician age and form part of a magmatic arc. (2) The La Escalerilla granite is a deformed biotite monzogranite and consists of a single elongated pluton; its relation with the other granitoids is not clear. (3) Garnet-biotite-muscovite granodiorites and granites and pegmatites. The granitoids have S-type signatures, with high 87Sr/86Sr and La/Yb ratios. They are possible crustal magmas related to a thickened crust and are interpreted as early-to syn-orogenic.(4) Biotite-and biotite-hornblende granites and minor tonalites of Devonian to Early Carboniferous age. The granites form large, post-orogenic, plutons and batholiths related to crustal uplift, and represent the last igneous activity of the Famatinian cycle (and also of the Palaeozoic era) in the Sierra de San Luis.Roqu6 et al. (1981) as that which produced the LLAMBiAS, E.

No abstract

[1] In the Sierra Norte de Córdoba, Argentina, at the inferred western pre-Andean Gondwana margin, structural analyses show that Upper Proterozoic-Lower Cambrian strips of metamorphic clastic rocks underwent two stages of a compressive deformational history. The D 1 deformation led to the formation of an S 1 cleavage/foliation and affected an older granite. It is related to F 1 folding around ∼N-S to NE-SW trending axes that partly record a steep plunge. Reconstructed fold structures display maximum wavelengths and amplitudes on a scale of hundreds of meters to kilometers. A steep to overturned dip of thick packages of metaconglomerates and metasandstones is related to this folding event. Also, because of variably oriented L 1 lineations and dextral shearing, structures of the D 1 deformation are assigned to different structural domains interpreted as the result of strain partitioning during dextral transpression. Strips of post-D 1 granite and clastic mylonites with a dextral sense of shear are attributed to the second-stage deformational event. The late stage dextral shearing and mylonitization locally affected intrusions of granites and dacitic porphyries. In the country rocks it took place along preexisting S 1 planes or locally developed S 2 /C 2 planes related to F 2 fold structures with steeply plunging axes. The regional metamorphism accompanying the deformation was in the range of the subgreenschist facies-greenschist facies transition and greenschist facies. The emplacement of synkinematic intrusions presumably followed active dextral shear zones. It cannot be excluded that during compressive deformation, older (normal) fault lines were reactivated and caused strain partitioning and later dextral shearing. After cessation of compressive deformation, granites and granodiorites intruded the deformed clastic succession and led to contact metamorphism of variable extent. Younger high-level intrusions record chilled margins also at angular xenoliths. Isotopic dates from granitoids, dacites, and metaclastic rocks in the Sierra Norte area and surroundings suggest that compressive deformations and metamorphism took place during the Early Cambrian Pampean orogeny. The deformational and metamorphic history can be attributed to either ridge subduction/collision or collision of the Pampean terrane with the western pre-Andean Gondwana margin. The two-stage kinematics suggests that (oblique?) collision was followed by a change to dextral displacements in the upper plate during the final state of and after collisional tectonics. The Sierra Norte area represented the upper (eastern) plate as supposed part of the Río de la Plata craton and its cover, overriding the lower plate that consisted of an accretionary complex in the west.

U-Pb zircon data (secondary ion mass spectrometry [SIMS] and thermal ionization mass spectrometry [TIMS] analyses) from igneous rocks with differing structural fabrics in the Sierra Norte de Córdoba, western Argentina, suggest that the sedimentary, tectonic, and magmatic history in this part of the Eastern Sierras Pampeanas spans the late Neoproterozoic-Early Cambrian. A deformed metarhyolite layer in metaclastic sedimentary rocks gives a crystallization age of 535 ± 5 Ma, providing a limit on the timing of the onset of D 1 deformation and metamorphism. The new data coupled with published Neoproterozoic zircon dates from a rhyolite beneath the metaclastic section and detrital zircon ages from the section indicate a late Neoproterozoic to Early Cambrian depositional age, making this section time equivalent with the Puncoviscana Formation (sensu lato) of northwest Argentina. A synkinematic granite porphyry gives a crystallization age of 534 ± 5 Ma, providing a limit on the age of dextral mylonitization in the Sierra Norte area (D 2 event). The new age is consistent with ages of 533 ± 4 Ma from a mylonitic granite with dextral sense-of-shear fabrics and 531 ± 4 Ma from a late-synkinematic dacitic porphyry, which broadly indicates the final age of dextral deformation. A crystallization age of zircons from the postkinematic, high-level El Tío granite (530 ± 4 Ma) suggests that both stages of Pampean deformation and regional metamorphism, accompanied by synkinematic intrusions, were followed by uplift and took place during a very short time span in the Early Cambrian. This is supported by zircon dates of 523 ± 5 Ma from a rhyolite to dacite in the western part of the Rodeito area and dates from the undeformed El Escondido rhyolite and granite of 519 ± 4 Ma and 521 ± 4 Ma, respectively. These three crystallization ages also indicate that ductile dextral shearing and mylonitization associated with the Pampean D 2 event terminated in the Early Cambrian. Both stages of Pampean deformation in this segment of the western pre-Andean Gondwana margin seem to represent a continuous event that can be related to oblique dextral convergence between the overriding plate in the east and the subducting and finally colliding plate in the west. The postkinematic intrusions and extrusions are related to the late stage of the Pampean magmatic history, which terminated before Early Ordovician (Famatinian) time.