Petrochronological approach for constraining P-T-D-t paths in mylonitic metapelites from Votuverava Group

Abstract

The Southern Ribeira Belt in Southern Brazil comprises several tectono-metamorphic terranes, with their own signature and metamorphic history, delimited by a network of regional scale shear zones. These terranes were accreted and recorded metamorphism and deformation mainly during the Brasiliano-Pan African cycle, related to the consolidation of the Western Gondwana. However, the existence of older Mesoproterozoic and Paleoproterozoic rocks in the Southern Ribeira Belt raises the possibility of previous tectonic cycles(s) that could have contributed to its current setting. The Anta Gorda Anticlinorium is a structural domain of the Apiaí Terrane that comprises Statherian orthogneissic mylonitic rocks and a Calymmian metasedimentary rock succession. Metamorphism in the metapelites ranges from the biotite zone grade to the kyanite zone. The metamorphic gradient suggests higher temperatures at more distal areas from the orthogneissic rocks but the metamorphic record is also strongly controlled by the bulk rock composition. The anticlinorium is surrounded by regional scale steep shear zones resulting in a framework of a large-scale strain partitioning model, with main shearing deformation coeval with peak metamorphism. The combination of monazite U-Th-Pb in situ dating with petrological modeling in the metapelites will allow Pressure-Temperature-Deformation-time (P-T-D-t) paths to be refined; those are critical to deepen our understanding of the possible thermal and deformation regimes that acted during the evolution of the Southern Ribeira Belt. This internship project proposal is based on a detailed petrochronological study combining quantitative compositional mapping of garnet- and monazite-bearing samples, phase equilibria modeling and monazite dating by LA-ICP-MS. (AU)