Structural evolution of the Sierra de San Luis (Eastern Sierras Pampeanas, Argentina): implications for the Proto-Andean Margin of Gondwana

Abstract

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.

Regional deformation of the Sierra de San Luis, Argentina: Implications for the Paleozoic development of western Gondwana

“…[20] Most existing models for the development of the convergent western margin of Gondwana view the Sierra de San Luis and the Sierras de Córdoba as a single interrelated tectonic unit beginning with Late Precambrian deposition of coeval turbiditic sequences [Ramos, 1988;Prozzi, 1990;Von Gosen and Prozzi, 1998]. Initial D1 pressure solution cleavage and chevron folding within the Sierra de San Luis and similar structural features in the Tuclamé Fm., northeast of the Tres Arboles fault zone in the Sierras de Córdoba, both indicate orthogonal shortening prior to peak metamorphism .…”

“…Well-exposed plutonic and metamorphic rocks and zones of ductile deformation within the Eastern Sierras Pampeanas provide evidence for a succession of Early Paleozoic tectonic events, including the Cambrian Pampean Orogeny Gromet and Simpson, 1999], the Early to Middle Ordovician Famatinian Orogeny Sims et al, 1998], and possibly the Ocloyic and/or Achalian Orogenies (Late Ordovician through Middle Devonian [Sims et al, 1998;Stuart-Smith et al, 1999]). Most previous work has viewed the Sierras de Córdoba and the Sierra de San Luis as an interrelated unit throughout the early Paleozoic [Ramos, 1988;Prozzi, 1990;Von Gosen and Prozzi, 1998], and therefore subject to consistent styles of deformation and metamorphism. However, recent work [Simpson et al, 2001;Whitmeyer and Simpson, 2003] suggests that the Sierra de San Luis was not positioned adjacent to the Sierras de Có rdoba prior to the Late Ordovician, which requires a reevaluation of the Paleozoic tectonic development of western Gondwana.…”

The tectonic significance of K/Ar illite fine-fraction ages from the San Luis Formation (Eastern Sierras Pampeanas, Argentina)

“…They are predominantly constituted by metapelites and metapsammites with layers of amphibolites and deformed crustal derived granites. Only in the Nogolí Metamorphic Complex, the appearance of large volumes of orthogneisses has been described (Ortíz Suárez et al 1992;von Gosen and Prozzi 1998;Sims et al 1998). In the central and southern part of the sierra, the basement domains are separated by the low-grade metamorphic sequences of the San Luis Formation (Fig.…”

Ordovician back arc foreland and Ocloyic thrust belt development on the western Gondwana margin as a response to Precordillera terrane accretion

“…The s and d kinematic indicators in both orthogneisses with mylonite textures to the north and marbles to the south suggest left-lateral motion [Martino and Astini, 1998b]. Oblique sinistral reverse to partly sinistral strike-slip displacements have also been inferred along the boundary between the Precordillera terrane and the Sierras Pampeanas (Valle Fértil lineament, Figure 12) and considered as a possible result of indenting during collision [von Gosen and Prozzi, 1998]. …”