Composition, structure and origin of the pluton of the Pampa del Tamboreo (San Luis province, Argentina)

Abstract

Two great granitie facies of regional significance can be distinguished in the central Sierras Pampeanas. One of them is a porphyraceous
pink granite, and the other is an equigranular, grey and biotitic facies; the pluton studied in this paper belongs to the last variety. Petrographically, two extreme compositions were distinguished within the body, one of them is tonalitice and the other is granitic. The xenolites, an aplite and the country rocks are also described, as well as the structures which are both in the main body and in the rock-walls, The granitic body has eruptive-concordant features. From mineralogic and textural comparisons of the two varieties the author infers that the tonalitic facies was formed first and this is due only to the metamorphism, without magmatic contribution, which provoked the consequent ?movilization? and intrusion of the whole complex. The concordant character is interpreted as that of a body lodged in the centre of an anticlinal (Facolito).