Estructura, fábrica magnética y emplazamiento de los granitos de Brealito y La Paya, basamento del valle Calchaquí, Salta, Argentina

Abstract

The Brealito and La Paya granitoids are elliptical-shaped plutons with N-S elongation. They intrude into the Puncoviscana and La Paya Formations, respectively. The internal structure of these plutons has been studied by using field structures and applying the Anisotropy of the Magnetic Susceptibility (AMS). The magnetic fabric of the La Paya pluton reflects the orientation of biotite, the main paramagnetic mineral in this granite (K between 1.9 and 6.7 x10-5SI). Instead, the magnetic behavior of the Brealito granite is more complex since not only paramagnetic minerals, but also the ferromagnetic contribution (K between 22 and 466 x10-5SI) of magnetite crystals strongly control the magnetic fabric of some samples. Total anisotropy values of the magnetic fabrics are coherent with the magmatic nature of the analized samples. From the structural point of view, both plutons display similarities. These granites are lozenge-shaped bodies concordant with the host rocks. Their planar fabrics are mainly NS-trending and West dipping, and magnetic lineations plunge at low angles along the N-S direction.