Age and geochemical composition in rutile: refining provenance analyses based on relationships between U-Pb ages and elemental ratios

• Grant number: 24/13473-9
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Effective date (Start): September 01, 2024
• Effective date (End): August 31, 2025
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geology
• Principal Investigator: Rodrigo Irineu Cerri
• Grantee: Tamiris Pagotti Gonçalves Pinto
• Host Institution: Instituto de Geociências e Ciências Exatas (IGCE). Universidade Estadual Paulista (UNESP). Campus de Rio Claro. Rio Claro , SP, Brazil
• Associated research grant: 22/06156-1 - Tracing the onset and evolution of plate tectonics with detrital rutile, AP.GR

Abstract

The Andrelândia Group (Neoproterozoic) is situated in the Brasília Orogen in the southern border of São Francisco Craton, being composed of two depositional sequences and four lithostratigraphic units. The Andrelândia Group succession consists of a nappe system (Andrelândia Nappe System), which developed fold-and-thrust belt structures due to the convergence between the Brasília and Ribeira orogens. It can be divided into two predominant groups composed of metasedimentary packages: the upper and the lower nappes. Previous studies used zircon to date the rocks of the two depositional sequences of the Andrelândia Group. The age of the depositional sediments is 640 Ma for the upper sequence, starting from 950 Ma to the lower sequence. Metamorphic ages of 630-600 Ma were obtained for the upper nappes rocks, and considered coeval with their emplacement and subsequent crustal melting. Some younger metamorphic ages of 590-570 Ma were obtained to the lower nappes. Despite zircon U-Pb dating are well developed for the Andrelândia Group, metamorphic ages obtained from other Uranium-bearing minerals, like rutile, are still lacking. Rutile is a metamorphic mineral that occurs in medium to high-pressure rocks (stable in pressures between 1.0-1.2 GPa, and rarely occurs in magmatic and mineralized rocks), and forms in high-facies metamorphism. Rutile is recently being as a proxy for identifying subduction zones, since it is not stable under 1.0 GPa. Besides being a mineral passive to be dated U-Pb method, it is used to determine the peak temperature of metamorphism (Zr-in-rutile geothermometer), can incorporate several incompatible trace elements (High Field Strenght Elements - V, W, Zr, Ti, Hf, Nb e Ta; preserving the initial composition and characteristics of the primary rock in which the rutile was formed), and is also resistant to erosion and weathering. Thus, this project proposes applying the U-Pb geochronology and trace elements in rutile from Andrelândia Group rocks, which further enrich the Neoproterozoic evolutionary models of the Brasiliano Orogeny. Based on this information, this work aims the use of rutile for U-Pb dating and analysis of metamorphic events related to subduction zones in the Andrelândia region, comparing these with detrital rutile U-Pb ages data from Mesoproterozoic rift basins previously collected and analyzed (São João del Rei Basin), with the intuition of understating the metamorphic evolution and the relation between U-Pb ages and trace elements composition. The relationship between elemental ratios and U-Pb ages in rutile will potentially help to differentiate whether grains of the same age have distinct geochemical composition, refining the use of rutile, for example, as an indicator of sedimentary provenance.