The São Sepe granitic complex, state of Rio Grande do Sul, and the evolution of the Brazilian southeastern orogenic region granitic rocks

Abstract

A model of evolution for granitic rocks of the Southeastern Oregenic Region of South America is proposed, based mainly on data obtained from a detailed study of the São Sepe Granitic Complex, State of Rio Grande do Sul. The following scheme seems to apply to these Granitic rocks: 1. Granitic rocks varying in composition from granodiorites to monzonitic granites, usually with inequigranular textures and also sometimes with oriented fabrics. SIN-TECTONIC: 700 to 610 m. y. (paroxism at about 650 m. y.). 2. Equigranular granites, mainly reddish-rose in color (may also be grayish). They present a sub-alkaline chemistry and occur mostly associated with the former group or as smaller independent plutons. Contacts present metamorphic aureoles. POST-TECTONIC: 570 - 500 m. y. 3. Volcanic or sub-volcanic acid rocks and related pyroclastics usually rhyolitic in composition. Structurally and/or chronologically associated with the post-tectonic granites. POST-TECTONIC: 520 - 430 m. y.