PRECAMBRIAN GEOLOGY OF THE RIBEIRÃO BRANCO TOPOGRAPHIC SHEET REGION AT THE SCALE OF 1: 50.000, SOUTHEAST OF THE STATE OF SÃO PAULO

Precambrian geology of the Ribeirão Branco topographic sheet region at the scale of 1:50,000, southeast of the São Paulo state

Abstract

The Ribeirão Branco Topographic Map, at a 1:50,000 scale, is located in the southeastern region of São Paulo state and lies within the south-central portion of the Ribeira Belt, specifically in the northern segment of the Apiaí Terrane. The area encompasses metavolcano-sedimentary lithologies of Meso- to Neoproterozoic age, including units of the Itaiacoca Group and the Açungui Supergroup, the latter represented by rocks of the Água Clara Formation. Also present are Neoproterozoic syn- to late-collisional granitoid rocks of the Capote Granite, associated with the Três Córregos Granite Complex, as well as post-collisional satellite stocks such as Sguario, Campina do Veado, and Santa Blandina. Sedimentary units from the Paraná Basin, comprising the Furnas and Itararé groups, are also found, along with basic intrusive rocks correlated with the Serra Geral Magmatism and recent Quaternary sediments. The geological evolution of the region reflects a Neoproterozoic tectono-metamorphic framework marked by three deformational phases. Two of these are associated with collisional, tangential tectonics, responsible for the emplacement and deformation of syn-collisional granitoids. The final phase, transcurrent to transpressive in nature, is related to the magmatic ascent of post-collisional stocks. Regional metamorphism is of the Barrovian type, characterized by high greenschist to amphibolite facies, with local occurrences of contact and dynamic metamorphism exhibiting retrograde features. The syn-collisional granitoids display high-potassium, peraluminous, I-type Cordilleran signatures, typical of magmatic arc settings, and are interpreted to result from partial melting of lower crustal rocks. The post-collisional stocks are associated with high-potassium to shoshonitic calc-alkaline series, displaying I-type Caledonian affinities, and are locally linked to alkaline peraluminous granites. This magmatic activity represents the concluding evolution of the Ribeira Magmatic Arc construction and defines the final geotectonic configuration during the stabilization of the Apiaí Terrane.