Petrology of Meso-Cenozoic alkaline mafic magmatism of the southeastern part of the Brazilian Platform (SP): lamprophyre dikes and cumulitic stocks

Abstract

This research project aims to contribute to the better knowledge of the Meso-Cenozoic alkaline mafic magmatism of the Brazilian Platform in the state of São Paulo, particularly in the Serra da Mantiqueira area. Firstly, work will be focused on petrographic, whole-rock and isotopic geochemical analysis of lamprophyre dikes. Through the recognition of mineral assemblages and the determination of geochemical and isotopic compositions we will be looking for specific signatures that help to infer the type of mantle source that could generate these rocks. On a second step, the mineral chemistry for major and trace elements of the most important phases of these dikes will be investigated. This would allow a better understanding of the crystallization processes, more specifically of the bearing glassy matrix lamprophyres classified as monchiquites. Based on the results, it will be possible to determine the crystal/liquid partition coefficients for minerals such as clinopyroxene and olivine that invariably are present as phenocrysts in these rocks. Moreover, it is our intention to proceed with the program of punctual complete chemical analyses of early crystallized phases from mafic-ultramafic cumulates that occur closely associated with the dikes and which initial liquids have a composition possibly related to the latter rocks. Thus, the main contribution of the project is reaching a better understanding of the magmatic types found in the series of alkaline dikes and of the formation of cumulitic bodies, including their respective magmatic evolution tendencies, and rising information on the mantle source of these rocks. With the new data we hope to reduce the shortfall in the literature of detailed works dealing with magmas of alkaline tendency in the context of the Brazilian Platform. (AU)