GEOLOGIA E PETROLOGIA DOS COMPLEXOS MÁFICO-ULTRAMÁFICOS DE MANGABAL I E MANGABAL II, SANCLERLÂNDIA, GOIAS

MARIA ÁNGELA FORNONI CANDIA, VICENTE ANTONIO VITÓRlO GIRARDI

Resumo


Mangabal I and Mangabal II are differentiated mafic-ultramafic bodies intrudíng gneissic terrains belonging to the Goiano Basal Complexo Although tectonicaly deformed and recrystallized, they still preserve characteristic features of stratiform igneous complexes formed by magmatic differentiation. In Mangabal I, the igneous stratigraphy is as fallows: the basal ultramafic sequence, made up of feldspathic peridotites, is followed by olivine gabbronorites; the top sequence ís formed of gabbronorites. In Mangabal II, the ultramafic basal sequence is composed of feldspathic harzburgites and feldspathic bronzítites, followed by olivine gabbronorites, overlain in turn by gabbronorites. The igneous paragenesis indicates that the complexes were formed by processes of low pressure fractional crystalization of a basaltic magma. Study of the metamorphic paragenesis and analyses of fluid inclusions indicate that subsolidus reequilibrations occurred at temperatures of 700-780°C and total pressures of 6-6,6 kb. The metamorphic paragenesis was also controlled by variations in PCO2 and PH2O of the fluid phase.

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