Understanding the mantle heterogeneities and the diamond potential of the Alto Paranaíba Region (Brazil): compositional signatures of xenocrysts in kimberlite intrusions

Abstract

This proposal for a BEPE scholarship is part of the ongoing collaborative studies among researchers from USP and University of Alberta (CAN). The student, Julia C. Bandeira Lino de Souza, will focus her undergraduate conclusion monograph on studying mantle xenocrysts from two specific hypabyssal intrusions in the province: Pântano (Limpeza-18) and Forca (Forca-01). The aforementioned selected intrusions are already being studied by the student Julia C. Bandeira Lino de Souza under the FAPESP Scientific Initiation Project (SIP) "Petrographic, Compositional, and Structural Characterization of Mafic Minerals Associated with Cretaceous Kimberlite and Kamafugite Intrusions in the Alto Paranaíba Igneous Province" (Proc. 2022/10522-3).This project aims to gain insight, through in situ, punctual analytical techniques of mineral microanalyses, into relatively unexplored aspects of the kimberlitic occurrences in the Alto Paranaíba Igneous Province (MG-GO, Brazil). The primary goals of the project are: (1) compositional characterization (major, minor, and trace elements) of mantle minerals (xenocrysts) present in rocks of kimberlitic affinity; (2) discussion of sources, intensive parameters (pressure, temperature, oxygen fugacity), their lateral and vertical heterogeneities, and potential metasomatic signatures induced by fluids and/or melts that enriched the mantle; and (3) how these factors may influence the diamond potential of the region.The analytical program involved entails in situ point analyses of trace element mineral chemistry using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA ICP-MS) in mantle xenocrysts carried by kimberlites (such as olivine, pyroxene, garnet, spinel, ilmenite, and zircon) from known samples that offer fresh and well-preserved material for these purposes. Major and minor element determinations will be conducted via electron microprobe, primarily in Brazil during the second half of 2023, with potential supplementary work in Canada depending on scheduling. All the analyses of trace elements in minerals will be carried out in the internationally renowned Arctic Resources Geochemistry Facility, affiliated with the University of Alberta. This facility specializes in geochemical microanalitical techniques (trace elements, isotopic ratios, and in situ geochronological dating - see https://www.eas.ualberta.ca/arctic-resources/?page=home for more information). They utilize state-of-the-art equipment and employ analytical protocols at the cutting edge of knowledge. In addition to the determination of trace elements in mantle xenocrysts in state-of-the-art laboratories, the internship period will facilitate data reduction and processing using specific software (Iolite for data reduction and quality assessment, and PTEXL spreadsheet for intensive parameter calculations). These data will be discussed with an integrated research group, known for their expertise in the studies of mantle materials and their complex evolution, led by one of the foremost current researchers in the study of mantle rocks and kimberlites, Professor Dr. D. Graham Pearson. (AU)