Identification and quantification of the processes that generate granite rocks based on textural, chemical and isotopic analyses of their minerals

• Grant number: 25/07684-0
• Support Opportunities: Regular Research Grants
• Start date: September 01, 2025
• End date: August 31, 2028
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geology
• Principal Investigator: Valdecir de Assis Janasi
• Grantee: Valdecir de Assis Janasi
• Host Institution: Instituto de Geociências (IGC). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated researchers: ADEJARDO FRANCISCO DA SILVA FILHO ; Adriana Alves ; Bruno Vieira Ribeiro ; Claudia Beatriz Zaffarana ; Cláudia Regina Passarelli ; Ignez de Pinho Guimarães ; Lucelene Martins ; Maria de Fátima Aparecida Saraiva Bitencourt ; Max Schmidt ; Silvio Roberto Farias Vlach

Abstract

Many fundamental questions about the origin of granitic rocks, and consequently the processes that generated and modified the Earth's continental crust, can be investigated through the textural and geochemical study of the minerals that constitute these rocks. In this project, we will draw on knowledge accumulated in previous studies carried out on selected occurrences of granitic rocks by our research group and by other groups that are associated here to investigate some of these processes. The main objectives of this project include: (1) The identification of source areas of granitic magmas, which will make use of proxies of great interpretative power, especially in situ isotopic data for the Rb-Sr system, including Rb-bearing minerals such as alkali feldspar and micas, based on recent improvements in the LA-MC-ICP-MS and LA-QQQ-ICPMS techniques, in addition to the Pb-Pb isotopy in feldspars and Lu-Hf in zircon; (2) Identification of the geochemical and isotopic signature of the enriched mantle generated and/or mobilized during the major event of granitic magma generation in the Brasiliano cycle in the Araçuaí-Ribeira Orogenic System (in addition to similar occurrences in the Borborema Province and the Dom Feliciano Belt) through the study of basic and intermediate potassic rocks; (3) The crystallization conditions of magmas generated at different stages of tectonic evolution, based on the composition of major and trace elements in minerals: O2 fugacity using zircon (Ce), apatite (S, Ce, Eu), titanite (Al, Fe), plagioclase (Eu); temperatures using methods independent of whole-rock composition (Ti in zircon; Zr in titanite and hornblende); pressure using the traditional Al method in hornblende; and (4) The thermal history of plutonic bodies (thermochronology), which will be investigated by combining geochronological methods on minerals with different closure temperatures for the various isotopic systems in minerals such as zircon, titanite, apatite, feldspars and biotite. (AU)