Petrogenetic evolution of kamafugites from the Late-Cretaceous Goiás Alkaline Province (GAP), Central Brazil.

BROD, J. A.; BARBOSA, E. S. R.; JUNQUEIRA-BROD, T. C.; GASPAR, J. C.; PETRINOVIC, I. A.; SGARBI, P. B. A.

Cabo Frío

Congreso; III Simpósio Sobre Vulcanismo e Ambentes Associados, 2005; 2005

GSB

                Abstract – The Late-Cretaceous Goiás Alkaline Province, located at the northern margin of the Paraná Basin, in central Brazil, is one of the largest areas of kamafugite exposure in the world. The northern portion of the province is dominated by alkaline plutonic ultramafic to mafic complexes, with subordinate dykes, plugs and sills. The central part is characterized by kamafugitic diatremes, plugs, and dykes, and the southern portion consists dominantly of kamafugitic lavas and pyroclastics. Within the GAP kamafugitc series, katungites represent the most primitive rock-types, and ugandites correspond to the most evolved magmas within the kamafugite series. However, the various kamafugitic rock-types cannot be easily connected through fractional crystallization. Elemental ranges of katungitic and mafuritic rock-types with MgO suggest that these groups represent independent sequences of rocks produced by various degrees of partial melting. Ugandites may also constitute an independent group or they may be the product of fractional crystallization of mafurites. Leucite mafurites are best explained as a result of mixing between picritic and mafuritic magma. This contrasts with the behaviour of the less silica-undersaturated rocks that form the northern GAP plutonic complexes, which is indicative of a derivation from an alkaline picrite parent magma, through fractional crystallization.