The oldest rocks of the Sao Francisco Craton: Geological characteristics and tectonic significance

• Grant number: 18/25465-0
• Support type: Regular Research Grants
• Duration: March 01, 2019 - May 31, 2021
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geology
• Principal Investigator: Elson Paiva de Oliveira
• Grantee: Elson Paiva de Oliveira
• Home Institution: Instituto de Geociências (IG). Universidade Estadual de Campinas (UNICAMP). Campinas , SP, Brazil
• Assoc. researchers: Cristina Talavera Rodriguez

Abstract

The study of Earth's primitive crust, the mechanisms responsible for its formation and evolution are important topics to understand the origin and differentiation of the continental crust, formation of the first cratons, and when plate tectonics began in our planet. The oldest rocks on Earth are mostly gneiss complexes that occur in cratonic blocks within high-grade metamorphic terrains of Palaeoarchaean to Hadean ages. The São Francisco craton, especially the Gavião block contains Brazil's oldest rocks formed 3.3- to 3.5-billion years ago. The Gavião block is composed mainly of gneisses of varied compositions, greenstone belts and other supracrustal sequences. Unpublished geochronological data have unravelled gneisses within the Gavião block older than those already known, with ages between 3.6 and 3.7 Ga, which may represent the most primitive area where the South-American continent began to form. Those rocks and similar gneisses from two other localities within the São Francisco craton will be studied in this project. The methods include field observations, petrography, zircon U-Pb geochronology, whole-rock major and trace element geochemistry, whole-rock 146Sm-142Nd isotope geochemistry, Hf and O isotope analyses of zircon grains with the objectives of contributing to the discussion of how was the Earth in its infancy and how it evolved with time. (AU)