Using petrochronology to understand the tectonometamorphic evolution of the Curitiba Domain, Ribeira Belt, SE Brazil

• Grant number: 19/19651-8
• Support Opportunities: Scholarships abroad - Research Internship - Master's degree
• Start date: February 01, 2020
• End date: July 31, 2020
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geology
• Principal Investigator: Renato de Moraes
• Grantee: Bruna da Silva Ricardo
• Supervisor: Catherine Mary Mottram
• Host Institution: Instituto de Geociências (IGC). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Institution abroad: University of Portsmouth, England
• Associated to the scholarship: 18/01572-1 - Petrochronoogy applied to the study of the tectono-metamorphic context of rocks from the Turvo-Cajati Formation, Curitiba Domain, and its role in the evolution of Ribeira Belt, Cajati, SP, BP.MS

Abstract

In Ribeira Belt, SE Brazil, metasedimentary rocks of distinct pressure conditions crop out. However, they are all assumed to be part of the same unit, the Turvo-Cajati Formation (TCF). A better understanding in P-T-t paths in this unit could help have a better picture of the conditions that lead to their current disposition. TCF is a metasedimentary unit forming the Curitiba Terrane, a major segment of the southern Ribeira Belt. It is composed of rocks of greenschist (Low-TCF), amphibolite (Medium-TCF) to granulite (High-TCF) facies conditions. Previous studies in High-TCF indicates that the unit underwent extensive partial melting under high-pressure conditions (670-810ºC and 9.5-12 kbar), within the kyanite stability field. In this MSc project, we detail the study of the metamorphic zoning within Low and Medium-TCF. The P-T investigation is made using petrography and pseudosection modeling in the NCKFMASHTO and MnNCKFMASHTO systems. Four metamorphic zones were recognized for the Low-TCF and Medium-TCF: biotite, garnet, staurolite and sillimanite zones, with pressures below 8 kbar, as staurolite breaks down straight to sillimanite, without formation of a kyanite zone, suggesting the different parts of the TCF experienced distinct metamorphic histories. This internship aims to use cutting-edge petrochronology techniques to determine the timing of inverted metamorphism in the TCF. Combining in-situ U-Th-Pb dating of accessory phases, geochemical analyses and pseudosection modeling will allow P-T-t paths to be determinate for TCF sub-units. Furthermore, analysis of novel medium and low-temperature geochronometers such as apatite and calcite will allow for deformation processes to be determined in distinct pressure regimes. Overall, this project will facilitate collaboration between the University of São Paulo and the University of Portsmouth, UK, allowing for access to world-leading geochronology expertise and facilities. This project will therefore allow for the collection of high-quality in-situ data, the results of which will make a major contribution to the regional geology of the Ribeira Belt, SE Brazil. By comparing metamorphic ages in High-TCF and Medium-TCF, we can better understand the relation of the metamorphic ages of both units and its tectonic disposition. The results will therefore have significant impact for how geologists understand tectonometamorphic deformation processes through the crust through geological time and will have widespread implications for how petrochronology is used to quantify deformation events worldwide. (AU)