U-Pb Geochronology of the Andrelândia Group: Refining the age of the metamorphism and probable source areas

• Grant number: 25/01211-2
• Support Opportunities: Scholarships abroad - Research Internship - Scientific Initiation
• Start date: March 17, 2025
• End date: June 27, 2025
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geology
• Principal Investigator: Rodrigo Irineu Cerri
• Grantee: Tamiris Pagotti Gonçalves Pinto
• Supervisor: Richard Palin
• Host Institution: Instituto de Geociências e Ciências Exatas (IGCE). Universidade Estadual Paulista (UNESP). Campus de Rio Claro. Rio Claro , SP, Brazil
• Institution abroad: University of Oxford, England
• Associated to the scholarship: 24/13473-9 - Age and geochemical composition in rutile: refining provenance analyses based on relationships between U-Pb ages and elemental ratios, BP.IC

Abstract

The Andrelândia Group is located on the southern border of the São Francisco Craton and is situated in an interference zone between the Brasília and Ribeira Orogen, characterized by the presence of folds and thrusts. The group was formed from the collision between the Paranapanema and São Francisco Cratons in the Brasiliano Orogeny (Neoproterozoic). The Andrelândia Group is composed of two depositional sequences, the lower nappes and the upper nappes and includes four lithostratigraphic units. The study area, composed of metasedimentary packages, is oriented to the east with previous studies dating the depositional and metamorphic age of the two sequences using zircon. The depositional age of the sediments is 640 Ma for the upper sequence and 950 Ma for the lower sequence. The upper nappes show metamorphic ages of 630-600 Ma and the age of the lower nappes 590-570 Ma. U-Pb zircon dating in the Andrelândia Group is often used, but metamorphic ages obtained from other U-bearing minerals, like rutile, are still lacking. U-bearing minerals have been utilized in various studies to analyse sedimentary sources and the age of metamorphism, and a mineral that stands out is rutile, as it is highly resistant to weathering and transport, making it easier to characterize the source area and origin of the grain based on Nb and Cr concentrations. Rutile occurs in medium to high-pressure rocks with stability above 1.0-1.2 GPa and can be used to determine the peak temperature of metamorphism, as well as to identify subduction-related metamorphism, registering regions with low T/P metamorphic gradients, indicative of high- to ultra-high pressures related to plate tectonics. Rutile also provides information about the last metamorphic cycle (chemical composition, temperature, and age of metamorphic peak or cooling). Rutile is a mineral that preserves essential characteristics of the parental rock, which shows a series of chemical elements (High Field Strength Elements - V, W, Zr, Ti, Hf, Nb, and Ta) that assist in identifying the parental rock geochemical signature. Rutile's ability to record only a limited number of metamorphic temperature peaks during its formation makes it more valuable in geochronology, unlike zircon, which can preserve multiple age peaks associated with later recrystallizations. The objective of this project is to apply U-Pb geochronology in detrital rutile from the Andrelândia Group rocks, as this mineral can be used to identify the age of metamorphism, and it would help to enrich the Neoproterozoic evolutionary models. This project aims to understand the metamorphic evolution and the relation between U-Pb ages and the difference in the origin of grains with the same age but different sources using geochronological and geochemical analyses on detrital rutile. The main objective of this project is to date rutile from Andrelândia Group that is related to metamorphic events associated with subduction zones.