GEOLOGIA DA SEQÜÊNCIA VULCANO-SEDIMENTAR DE ALPINÓPOLIS (MG)

Abstract

The Alpinópolis Belt is located in the southern part of the State of Minas Gerais. It is one of several meta volcano-sedimentary sequences of the Morro do Ferro Greenstone Belt. As a result of surface geological mapping, petrological studies and subsurface exploration work conducted on the Alpinópolis region, a group of four rock suites have been recognized. The most important features of these four rock suites can be summarized as follows: The first suite comprises (a) chlorite-actinolite-tremolite schists with spinifex texture and minor olivine pseudomorphous; and (b) serpentinites with variable proportions of actinolite-tremolite-chlorite-talc-oli vine relicts and hornblende schists. The combined evidence of mineral assemblages, preserved primary textures and trace element chemistry indicate that these rocks were originally peridotites and pyroxenites of komatiitic affiliation. The second suite consists of a variable assemblage of plagioclase-homblende-actinolite-tremolite schists and amphibolites. The chemical and mineralogical features of this suite are consistent with a tholeiitic basalt origin. The third suite consists of metasedimentary rocks such as gamet-biotite schists, actinolite-tremolite-biotite schists, sillimanite-staurolite-biotite schists, gamet-antophylite schists, quartzites and minor iron formation units. The schists are interpreted to be isochemically metamorphosed tuffaceous, argillaceous and impure Fe-Mg-carbonate sediments. The aforementioned supracrustal rocks have been intruded by a number of granitoid rocks that consist of quartz, sódic-plagioclase and biotite. Near to and at the contact with the ultramafic flows, marundite rocks are observed. The policyclic tectonic-metamorphic and deformational processes which affected the area have given place to a complex, large scale structurally deformed framework and imprinted metamorphic patterns on the existing rock units and the associated Ni-sulphide ore bodies.