The effects of deformation-related processes on geochronological systems: clues from the southern Brasília Orogen (SE Brazil)

• Grant number: 23/06385-3
• Support Opportunities: Regular Research Grants
• Start date: September 01, 2023
• End date: February 28, 2026
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geology
• Principal Investigator: Caue Rodrigues Cioffi
• Grantee: Caue Rodrigues Cioffi
• Host Institution: Instituto de Geociências (IGC). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated researchers: Alice Westin Teixeira ; Brenda Chung da Rocha ; Bruno Vieira Ribeiro ; Christopher Kirkland ; Mario da Costa Campos Neto ; Vinícius Tieppo Meira

Abstract

The significance of geochronological data obtained from deformed rocks is dependent on several factors, including temperature, mineral composition, and pressure. Most importantly, deformation-related processes such as fluid circulation, recrystallization, and neocrystallization may play a major role on isotopic exchange in the mid-to-upper continental crust. In these settings, deformation occurs at temperatures close to or below the isotopic closure which makes deformation-related processes more effective mechanisms for isotopic exchange than thermally activated diffusion. In such circumstances, the obtained geochronological data may represent the timing of deformation-related processes instead of cooling ages. This project aims to investigate the effects of deformation-related processes on the geochronological systems in the southern Brasília Orogen nappe stack (SE Brazil), especially on the 40Ar-39Ar system, using the novel in-situ Rb-Sr technique by LA-ICP-MS associated with microstructural analysis and U-Pb dating of apatite and rutile. This approach has the potential to shed light on the final stages of the southern Brasília Orogen evolution and on fundamental questions of geochronology such as the effects of deformation-related processes on the 40Ar-39Ar systematics and the definition of isotopic closure temperatures for the Rb-Sr system in micas. (AU)