Elements mobility during fenitization processes: the carbonatite metasomatism in the Alto Paranaíba and Ponta Grossa Arch alkaline provinces

Abstract

The aim of this research proposal is to investigate the characteristics and effects of the metasomatic fluids related to the fenitization process that took place at the contacts between ultramafic rocks and carbonatites from different Brazilian occurrences: Salitre, Tapira, Araxá (Alto Paranaíba) e Jacupiranga (Arco de Ponta Grossa) complexes. Studies on alkaline-carbonatite units that disregard the role of fenites in the magmatic evolution can be seen as incomplete, since the segregation of the metasomatic fluid, alkali-rich, directly affects the carbonatite magma composition. The analytic schedule of this project comprises detailed petrography, whole-rock geochemical (major and trace elements) and isotopic (Sr, Nd and Pb) analyses, mineral chemistry (major and trace elements), in situ Nd and Sr determinations, O-C isotopic determinations and Ar-Ar geochronology. The combination of the aforementioned techniques will contribute to better constraint the original composition of carbonatite magmas, as well as to address important questions about the metasomatism described within the selected units, such as: (1) What are the compositional variations related to the mineral phases of the metasomatic paragenesis? (2) What are the characteristics and effects of the metasomatic fluids? (3) Which elements were fractionated and/or added to the carbonatite magma? and (4) What are the roles of the metasomatic fluids and of the carbonatite magma on the formation of the carbonate material from the reaction bands? This is an original proposal, both for the focus of the discussions to be addressed and for the type of analyses to be performed, neither of them properly explored in the study of metassomatism processes in the Brazilian alkaline-carbonatite units.