The Late Cretaceous Goias alkaline province (GAP) Central Brasil

BROD, A.; BARBOSA, S.R.; JUNQUEIRA BROD, T.; GASPAR, J.; DINIZ-PINTO, H.S.; SGARBI, P.B.A.; IVAN ALEJANDRO PETRINOVIC

Mesozoic to Cenozoic Alkaline magmatism in the Brazilian Platform

Editora da Universidad de Sao Paulo

Lugar: Sao Paulo; Año: 2006; p. 261 - 317

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 characterised by sub-volcanic bodies (diatremes, plugs and dykes) and the southern portion consists dominantly of volcanic rocks (lavas and pyroclastics). From north to south there is also a marked increase in the level of silica-undersaturation of the alkaline rocks, with a dominance of less silica-undersaturate (feldspar-bearing) rocks in northern GAP and of strongly undersaturate, kamafugitic (katungite, mafurite, leucite mafurite and ugandite) rocks in the central and southern parts of the province. Textural, mineralogical and geochemical evidence indicate a complex evolution of the GAP The mineralogical and chemical composition of the less silica-undersaturate rocks that form the northern GAP plutonic complexes are consistent with derivation from an alkaline picrite parent magma, through fractional crystallisation. Compositionally, katungites represent the most primitive and ugandites represent the most evolved magmas within the kamafugite series, but the various kamafugitic rock-types cannot be easily connected through fractional crystallisation. The trace element 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 represent an independent group or they may be the product of fractional crystallisation of mafurites. Leucite mafurites are best explained by mixing between a picritic and a mafuritic magma. The field relationships, and the chemistry of phlogopite and olivine suggest that the kamafugite-carbonatite association is significant in the central and southern GAP.