Abstract

SOLA, Alfonso M; BECCHIO, Raúl A  and  PIMENTEL, Márcio M. Pumayaco leucogranite: crustal anatexis during the Famatinian cycle in the northern end of the Sierra de Molinos, Salta Province. Rev. Asoc. Geol. Argent. [online]. 2010, vol.66, n.1-2, pp.206-224. ISSN 0004-4822.

In the Molinos Ranges, Salta, Argentina, basement units of low to high metamorphic grade (Puncoviscana and La Paya Formations) crop out, intruded by granitoid bodies of sieno-monzogranite composition and Early Ordovician age. These are folded sheetlike bodies of small dimensions (less than 10 km²), emplaced synchronously within deformation at mid-crustal levels. They are intimately linked with migmatic rocks and characterized by the presence of accessory minerals such as garnet, cordierite, sillimanite and tourmaline. The Pumayaco leucogranite is the largest of theses plutons and is located in the center of the Molinos range. Here we present a detailed mapping of the main granite, and separate different facies using petrographic and geochemical data. The alumina contents (ASI>1.1) and the narrow silica variations (72-76 %wt), as well as the petrographic features, allow to classify them as S-type granitoids derived from crustal anatexis. The processes that would have been involved in the generation and differentiation of these granitoids include different melting reactions of metapelite and metagreywacke protoliths, and an influence of restite phases in the segregated melt compositions. The association with ductile shear zones and the field relation with migmatic units suggest an important participation of deformation during segregation, migration and emplacement of these melts under a convergent tectonic regime (Famatinian Cycle).

Keywords : Leucogranites; Anatexis; Ductile deformation; Lower Paleozoic; Eastern Cordillera.

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