This master's degree project aims to study the trace element partition coefficient of phenocrysts in chemical equilibrium with their matrix (aphanitic, glassy or phaneritic fine-grained ones). The main targets are alkaline dykes of different composition, as lamprophyres and phonolite, outcropping in São Paulo state, Brazil.To reach its objective, the former steps of this project are the sample selection and petrographic analysis by optical microscopy and scanning electron microscopy. Finally, the complete chemical analysis (major, minor and trace elements composition) of these minerals and of each lithotype will be done. Bulk geochemical compositions will be analyzed by spectrometry techniques as X-ray fluorescence (XRF), inductively coupled plasma optical emission spectrometry (ICP-OES), and inductively coupled plasma mass spectrometry (ICP-MS). Chemical compositions of minerals will be determined by in situ, punctual, microanalysis techniques, as wavelength-dispersive spectrometry (WDS) by electron microprobe and laser ablation ICP-MS.These new data will be treated and discussed focused on the trace element partitioning among coexisting mineral phases correlating the magnitude of their enrichments relatively to the bulk-chemistry of the system and to their crystalline structures. The theoretical treatment of the results will be based on the "crystal lattice strain" models. These models mention the influence of characteristic sites of crystalline structure of the different minerals in the partitioning behavior of trace elements. Finally, the study will lead to discussions of the variations in the behavior of trace elements in minerals crystallized in different liquid compositions.This mineralogical study will be of great importance for the interpretation magmatic evolution in the context of the alkaline magmatism in the southeastern part of Brazil, since there are few experimental studies reported in the literature investigating the trace element partitioning between mineral and alkaline magmas. The project represents a first approach to the theme from rocks related to the Meso-Cenozoic magmatism in the Brazilian Platform, adding an innovative theme to the traditional line of research associated with the petrological study of alkaline magmatism of the IGc-USP.
News published in Agência FAPESP Newsletter about the scholarship: