Study of the Brasilia Belt in the Northwestern Passos Nappe Region

Abstract

The Passos Nappe is located at the Southern portion of the Brasilia Belt and records an inverted metamorphic gradient that increases from greenschist facies, at the bottom of the sequence, to high-pressure granulite at the top. Although several studies have been carried out in the area, detailed mapping and metamorphic studies have never been carried out on its NW portion. In recent geological mapping campaigns, geological boundaries between the Internal Domain (Passos Nappe) and the External Domain of the Brasilia Belt have been better constrained. New geological units have been identified and the relationship of these units with the geologic evolution of the areas has to be better investigates. Taking into account the new findings, as well as previously available data, three questions need to be answered and are the main aim of this project: 1) the lack of geochronological data on the External Domain sequences that puts in check the stratigraphic correlations proposed by the literature; 2) the intriguing occurrence of garnet mega-porphyroblasts (3 to 7 cm in size) that occur in the middle portion of the sequence; 3) Is the metamorphic gradient continuous? Are the discontinuities within the sequence? This project proposal aims to answer these questions by means of U-Pb provenance studies in detrital Zircons, detailed in situ chemical studies of the garnet mega-porphyroblasts with electron microprobe, and termobarometric studies using the Zr in Rutile and Ti and Quartz geothermo(baro)meter. The results will support a better understanding of the tectonic and metamorphic evolution of the southern portion of Brasilia Belt. It will also support a better understanding of the deformational and metamorphic processes that are involved in the formation of orogenic belts. (AU)