La Costa pluton, an expresion of S- type magmatism in the northeastern sector of the Sierra de Velasco, Sierras Pampeanas

Abstract

Combined petrology, mineral chemistry and whole-rock geochemistry studies reveal the presence of two peraluminous granitic units with magmatic aluminous minerals, such as garnet and white mica, and the distinctive presence of tourmaline. The evidence presented here indicates that these two facies, Anillaco and Anjullón, together with the peraluminous Santa Cruz unit studied in previous works, constitute co-sanguineous rocks, emplacemed in shallow levels of the crust, conforming a greater igneous unit, named here as La Costa pluton, that outcrops in the northeast sector of the sierra de Velasco. The mineral assemblage, the mineral chemistry and the whole-rock geochemistry allow defining the La Costa pluton as classic S-type granitoids, derived of a source rock of dominant pelitic composition. Several studies demonstrate that a high geothermal gradient is required for the generation of S-types granitoids, thus the La Costa pluton indicates that the crust supported a remarkable heating in this region during the generation of the magma. However, the absence of geochronological data prevents identification of the tectomagmatic event that yielded the parental magma of this pluton.