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

Abstract

Metamorphic and ductile deformation fabrics within the Sierra de San Luis, central Argentina, provide evidence for the Early to Middle Paleozoic development of the paleo‐Pacific margin of Gondwana. Presumed Vendian‐aged metasedimentary rocks within both the Sierra de San Luis and the Sierras de Córdoba preserve early pressure solution cleavage development. Cambrian peak metamorphism in the Sierras de Córdoba and Ordovician peak metamorphism in the Sierra de San Luis indicate that juxtaposition of these two terranes did not occur prior to the Late Ordovician. Peak metamorphism and regional folding of the Sierra de San Luis metasedimentary rocks is equated with early stages of the development and shortening of the Famatinian magmatic arc along the western margin of Gondwana. Extensive, NNE trending zones of upper greenschist‐ to amphibolite‐facies ductile deformation within the Sierra de San Luis and along the western margin of the Sierra de Comechingones record the dextral oblique juxtaposition of the Sierra de San Luis terrane against the southwestern margin of the Sierras de Córdoba, coincident with, or closely followed by, the suture of the exotic Precordillera terrane to the western margin of Gondwana by the Early Devonian. Middle to Late Devonian restricted, lower greenschist‐grade reactivation of ductile faults may record the accretion of the Chilenia terrane, the final stage of Paleozoic convergent tectonism along this segment of western Gondwana.

Reinterpretation of the Ordovician rotations in NW Argentina and Northern Chile: a consequence of the Precordillera collision?

“…In the Late Ordovician to Silurian the back-arc basin was finally closed and inverted through thrusting and development of mylonitic belts (Astini and Dávila 2004) and S-type plutons associated to shear zones between 447 and 435 Ma Steenken et al 2004). In the Famatina Ranges this deformation is also characterized by dextral (Hongn et al 1999;Rapela et al 2001;Höckenreiner et al 2003;Whitmeyer and Simpson 2004;López et al 2007) and sinistral (Steenken et al 2004;López et al 2007) transpressive movements with associated normal faults (Dávila 2001). The development of a faulted back-arc basin within a thin continental crust (in some places almost quasi-oceanic, e.g.…”

“…The best known of these is the Tipa shear zone (López and Toselli 1993;Höckenreiner et al 2003) which extends in a NNW-SSE direction for several 100 km and shows high angle mylonitic belts of up to 2 km wide. In the San Luis Ranges also there is evidence of dextral ductile deformation (Sims et al 1998;Whitmeyer and Simpson 2004). These structures developed between the Ordovician and the Devonian and have apparently accommodated a significant crustal shortening between the Famatina and the Pampean Ranges blocks, during and after the collision of the Precordillera Terrane.…”

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

“…Their thermobarometric analyses indicate that the Loma de Las Chacras metasediments were migmatized at high pressure, and illustrate the difference with migmatites and gneisses developed toward the east (into the craton) that showed signs of a Barrovian type (medium temperature-medium pressure) metamorphism [Dalquist and Baldo, 1996;Baldo et al, 2001;González et al, 2002]. This more external region to the east (e.g., Sierra de Chepes, Sierras de San Luis) has also yielded Ordovician metamorphic ages averaging 470 Ma [Pankhurst et al, 1998;González et al, 2002;Whitmeyer and Simpson, (Figure 12), immediately west of Loma de Las Chacras [Ramos et al, 1998;. The previously described Early Ordovician, high-level low-grade metamorphism within the internal part of the Famatina thrust-fold belt is consistent with the ages of associated metamorphism and deformation elsewhere and, Figure 12.…”

“…Little direct evidence of related contraction has been documented involving the lower Paleozoic stratigraphy preserved in the Precordillera terrane with the exception of pre-Carboniferous west vergent duplexes affecting Ordovician limestones in the eastern Precordillera [von Gosen, 1992] and thin-skinned west vergent thrusts affecting the same limestone succession in the northern Precordillera [Astini, 1991[Astini, , 1992Thomas et al, 2002]. Within the back arc region, however, apart from the shear zones described within the Sierras Pampeanas and Famatina regions [Martino et al, 1993a[Martino et al, , 1993bMartino and Astini, 1998a;Northrup et al, 1998;Simpson et al, 1998Simpson et al, , 2003Conci et al, 2001;Whitmeyer and Simpson, 2004], no higher level structures have been associated to the Ocloyic deformation.…”

Mineral chemistry and chemical zoning in tourmalines, Pampa del Tamboreo, San Luis, Argentina

“…Three orogenic events with attendant deformation affected the basement of the Eastern Sierras Pampeanas to varying degrees and are related to the development of the western Gondwana margin (e.g. Whitmeyer and Simpson, 2004). Those events include (Sato et al, 2003) the Neoproterozoic-to-Cambrian Pampean Orogeny (probably 600-530 Ma), early Palaeozoic Famatinian Orogeny ($510-362 Ma) and the Devonian Achalian Orogeny (Sims et al, 1997(Sims et al, , 1998.…”