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Intensive parameters of crystallization (P-T-fO2) for kimberlites from the alto Paranaíba alkaline province and the diamond instability: the Três Ranchos IV e Limeira I intrusions

Grant number: 16/12627-6
Support type:Scholarships in Brazil - Master
Effective date (Start): March 01, 2017
Effective date (End): October 31, 2018
Field of knowledge:Physical Sciences and Mathematics - Geosciences
Cooperation agreement: Coordination of Improvement of Higher Education Personnel (CAPES)
Principal Investigator:Rogério Guitarrari Azzone
Grantee:Bruna Coldebella
Home Institution: Instituto de Geociências (IGC). Universidade de São Paulo (USP). São Paulo , SP, Brazil
Associated research grant:12/06082-6 - The Paraná-Etendeka magmatic province in Brazil: temporal and petrologic relationships between the tholeiitic and alkaline magmatism and geodynamic implications, AP.TEM

Abstract

The main question of this proposal deals with the influence that intensives parameters such as pressure, temperature and oxygen fugacity (T, P and fO2) can have in a greater instability of carried (or possibly carried) diamond xenocrysts in kimberlitic magmas from Alto Paranaíba Alkaline Province. This project will develop chemical analyses of the main mineral phases of different kimberlite intrusions to determine these crystallization's parameters. The special focus will be perovskite and monticellite crystals found in the fabric of these rocks. For such phases, specific calibrations based on oxygen fugacity experimental studies were developed. This will be will be the first approach to quantify and discuss the oxygen fugacity based on cognate phases from rocks of Alto Paranaiba alkaline province and to discuss the implications associated with the variation of this parameter. Furthermore, analyzes on garnet, olivine, chromite, spinel and ilmenite crystals (xenocrysts and cognate phases) will help in the temperature and pressure estimatimatives. Especially based on the pressure determinations it would be possible to indicate the depths sampled by these bodies, once most of the minerals chosen as geobarometers are representative of the mantle xenocrysts assembly that were carried by these magmas. Two intrusions will be the main focus of the analytical program, both belonging to the Alto Paranaiba Province: the Três Ranchos IV, described as diamondiferous, and Limeira I, defined as sterile. In addition, available chemical data for other intrusions of this province will be compiled and used to calculate these parameters for the entire province. Petrographic studies will be conducted in order to determinate the mineralogical compositions, textures and structures, as well as chemical analysis of major, minor and trace minerals. To achieve the proposed objectives, it will be necessary the utilization of various analytical methods such as Scanning Electron Microscopy (SEM), WDS by electron microprobe, laser ablation ICP-MS, and X-ray fluorescence. This research will contribute to the understanding of evolution and crystallization of kimberlite magmas from this Province, and to the understanding of the mantle sources sampled during their ascent. It will provide important parameters for the understanding of the economic potential associated with possible presence and preservation of diamonds in kimberlite rocks, as recent experimental work indicate a positive correlation between the oxygen fugacity fluctuation and the greater instability of diamond. It will also outline important considerations related to intensive variables of crystallization in the province as a whole and contribute to the understanding of underlying mantle. The project is a first approach to this subject from rocks related to the Meso-Cenozoic magmatism in the Brazilian Platform, adding an innovative theme to the traditional IGc-USP research line associated with the petrological study of alkaline magmatism. Also, it attends one of the goals outlined in the Thematic Project "The Paraná-Etendeka magmatic province in Brazil: temporal and petrological relations between tholeiitic and alkaline magmatism and their geodynamic implications" (FAPESP 2012/06082-6), to which it is linked, namely the petrological study of kimberlite magmas. (AU)