Faja de Deformación la Horqueta, sierra de Velasco, Sierras Pampeanas, NO de Argentina: Petrografía, geoquímica, estructuras y significado tectónico

Abstract

The La Horqueta Shear Zone (LHSZ) is the sixth shear zone recognized in the Sierra de Velasco, Sierras Pampeanas, NW Argentina. This shear zone separates two types of metagranitoids of contrasting petrographical and geochemical characteristics: metagranodiorites, outcropping towards the SW, consist in weakly peraluminous biotite-allanite-titanite granodiorites similar to the l-type granitoids of southern Sierra de Velasco and of neighboring ranges that are part of the Famatinian magmatic arc, while metagranites, outcropping towards the NE, consist of strongly peraluminous biotite-muscovite monzogranites identical to the Antinaco Orthogneis of northern Sierra de Velasco, which is part of an inner S-type granitoid belt. The LHSZ, developed from these two protoliths, has a thickness of 1 to 2 km and is composed of protomylonites and mylonites with strong NNW trending and E dipping mylonitic foliation. Cinematic analysis indicates a main transpressive deformational regime with an inverse-sinistral component, accompanied by a subordinate dextral transcurrent component, which possibly placed the two tectonic settings in contact.