Thermochronology applied to geotectonic modeling: the case of the Southern Brasília orogen, Brazil

Abstract

Thermochronology is a technique that applies chemical and isotopic systems in order to extract evidences on the thermal history of rocks, minerals and geological terranes. The comprehension of the thermal history, allied to other geological information, allows the establishment of the period/age of geological processes. This knowledge is essential to the understanding of Earth's evolution and the process involved, such as subduction, collision and exhumation.The main goal of this project is to test different models of the tectonic evolution of the Southern Brasilia Orogen reported in the literature, applying different thermochronological methods. The results will produce more evidences to understand the geotectonic mechanisms active during the Gondwana agglutination in the Neoproterozoic. The thermochronometers 40Ar/39Ar in hornblende, muscovite and biotite and U-Th-Pb in metamorphic zircon, titanite and monazite will be carried out in samples belonging to the different nappes of the orogen. These combined systems are among the most applied in thermochronology studies, with closure temperatures variable between 300 ºC and >900 ºC. Detailed petrographic analysis, cathodoluminescence and back-scattered electrons images of grains will be fundamental tools to discriminate crystals of different metamorphic phases and to identify possible compositional zoning on the minerals. Thus, the different stages of the metamorphic event that affected each one of the nappes will be carefully dated. (AU)