P-T-t reconstitution of the Metamorphic Trajectory of the Metatextites from the Base of the Liberdade Nappe, Andrelândia Terrain, a Petrochronological Approach

• Grant number: 24/01316-6
• Support Opportunities: Scholarships in Brazil - Master
• Start date: November 01, 2024
• End date: January 31, 2026
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geology
• Principal Investigator: Renato de Moraes
• Grantee: Catarina da Paz Roberto Ferreira
• Host Institution: Instituto de Geociências (IGC). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

The Liberdade Nappe is the intermediate unit of the Andrelândia Nappes System, which is inserted in the tectonic context of orogeny of the southern Brasília Orogen, dating from the Neoproterozoic. The rocks of Liberdade Nappe are described as metasedimentary rocks, pelitic schists, paragneisses, quartzites, calcisilicate rocks, amphibolites, metaultramafic rocks and retroeclogites. The focus of this project are the metatexites that occur at the base of Liberdade Nappe, which show a variety of lithotypes of different protoliths. Among them, three lithotypes will be studied: biotite-muscovite-garnet metatexite with kyanite and staurolite, kyanite-garnet-biotite-muscovite metatexite with staurolite and diopside-hornblende amphibolite metatexitic with titanite and retrometamorphic epidote. These rocks, previously studied in the candidate's bachelor thesis and Scientific Initiation (2022/09500-5), were thermodynamically modeled and presented concordant metamorphic peak conditions of 670-750 ºC at pressures of 9-10 kbar. Therefore, in order to reconstruct the P-T-t trajectory of the base of Liberdade Nappe, this project seeks to date the conditions of metamorphism of metatexites using different geochronological methods: U-Pb dating in zircon, monazite and titanite, related to ages close to the metamorphic peak of the rock; and Rb-Sr dating in micas, related to cooling. Associated with petrochronological studies, structural analysis will be carried out with rocks from the region, as well as microstructural studies on petrographic thin sections. Thus, the aim is to correlate the metamorphic trajectory calculated for the rocks based on iterative thermodynamic modeling (Bingo-Antidote program), with the ages obtained from different geochronological methods, in addition to interpreting associated regional structural features. In this way, it is expected to obtain results that contribute to understanding the evolutionary tectono-metamorphic framework of the southern Brasília Orogen.