FCT - Artigos publicados em periodicos
URI Permanente para esta coleção
Navegar
Navegando FCT - Artigos publicados em periodicos por Autor "Brod, José Affonso"
Agora exibindo 1 - 2 de 2
Resultados por página
Opções de Ordenação
Item Isótopos estáveis (C, O, S) e geoquímica de rocha total de carbonatitos da província Ígnea Alto Paranaíba – SE Brasil(2016-09) Gomide, Caroline Siqueira; Brod, José Affonso; Vieira, Lucieth Cruz; Junqueira-Brod, Tereza Cristina; Petrinovic, Ivan Alejandro; Santos, Roberto Ventura; Barbosa, Elisa Soares Rocha; Mancini, Luis HenriqueThe present work investigates the relationship between whole-rock geochemistry and stable isotope composition from carbonatites belonging to the Tapira, Araxá, Salitre, Serra Negra, Catalão I, and Catalão II alkaline-carbonatite complexes of the Alto Paranaiba Igneous Province (APIP), central Brazil and from the Jacupiranga Complex, of the Ponta Grossa Province, southeast Brazil. The APIP complexes are ultrapotassic, comprising bebedourites, phoscorites, nelsonites, and carbonatites, whereas Jacupiranga is a sodic complex composed of ijolite-series rocks, syenites, carbonatites, and alkaline gabbros. The geochemistry data allied to mineralogical constraints allowed us to classify the carbonatites into five groups, and to devise a chemical index (BaO/(BaO+SrO)) to gauge the magmatic evolution of the studied carbonatites.The APIP carbonatites evolve from apatite-rich calciocarbonatites toward Ba-, Sr-, and rare earth element (REE)-rich magnesiocarbonatites. This evolution is mostly driven by apatite, phlogopite, dolomite, and calcite fractionation and consequent enrichment in monazite, norsethite, and strontianite. Stable isotope data show a wide diversity of petrogenetic processes in play at the APIP, relatively to the Jacupiranga Complex, which is interpreted as a result of the shallower intrusion levels of the APIP complexes. Such shallower emplacement, at low lithostatic pressure, allowed for a complex interplay of fractional crystallization, liquid immiscibility, degassing, and interaction with hydrothermal and carbohydrothermal systems.Item Variações composicionais de olivinas do complexo alcalino-carbonatítico de Salitre, MG(2012-12) Barbosa, Elisa Soares Rocha; Brod, José Affonso; Cordeiro, Pedro Filipe de Oliveira; Brod, Tereza Cristina JunqueiraCompositional variation of olivines from Salitre alkaline-carbonatite complex, MG. The Salitre alkaline-carbonatite-phoscorite complex belongs to the Alto Paranaíba Igneous Province and consists of three separate bodies. Salitre I is a central, kidney-shaped body composed dominantly of bebedourites, with swarms of ring dykes of carbonatites and phoscorites; Salitre II and III are bebedourite-dominated smaller intrusions, respectively to the north and to the south of Salitre I. Olivine occurs in bebedourites, phoscorites and carbonatites, with forsterite content ranging from 83 to 98 mol. %. The least evolved rocks (bebedourites) show lower forsterite content than the more evolved members (phoscorites and carbonatittes), and olivine from carbonatites have the highest forsterite content. The compositional range of forsterite content observed in bebedourites is related to crystal fractionation. In phoscorites, forsterite content increases with decreasing whole-rock MgO, and in carbonatites it decreases, with the decreasing whole-rock MgO. Variations in CaO and MnO may occur in Salitre olivines. The controls of their distribution are unclear and may suggest local variations in the concentration of these elements in the magma, rather than a crystallographic control of olivine. NiO contents show differences between olivines from bebedourites, and olivines from phoscorites and carbonatites. This discrepancy may be related to the removal of Ni from the system by early fractionation of Ni-rich olivine from a silicate parental magma or, alternatively, by Ni removal in an immiscible sulfide liquid.