Caracterização da "Zona de Sutura" Jacui-Conceição da Aparecida, MG - limite norte do Cinturão Alto Rio Grande : im plicações geotectonicas e metalogeneticas

AUTOR(ES)
DATA DE PUBLICAÇÃO

1993

RESUMO

An are a in the Southwest of Minas Gerais, including the town of Petúnia, was divided into two distinct terrains, namely, Campos Gerais Belt and Petúnia Complex, both collectively called Campos Gerais Complex in earlier works. The former, and older, is an autochtonous terrain regarded as the basement to the latter. It is located in the northern part of the area and consists of migmatitic orthogneisses containinq greenstone belt sequences. Structural and metamorphic data show that this basement underwent amphibolite facies metamorphism was affected by transcurrent ductile shear zones, all with a general west-northwest strike, that underwent retrograde metamorphism to greenschist facies grade. The Petúnia Complex, considered allochtonous, is mostly made up of gneisses, with minor intercalations of psammitic and pelitic schists, possibly of supracrustal origino Between the cities of Jacui and Conceiçlo da Aparecida, the Petúnia Complex includes a discontinuous belt of metagabbros and metaultramafic rocks. These rocks are mostly foliated and may contain Os-Ir-Ru alloys and sulphides-bearing podiform chromitites, hosted by metaduni tic bodies, locally dif ferentiated. All these features suggest that the mafic anã ultramafic rocks may be the obducted slabs of an ophiolite sequence. The structural and metamorphic data indicate also that the Petúnia Complex underwent two tectonic events. The first is characterized by a tangential tectonics that produced ductile deformation, shear zones, regional foliation and mineral lineation, and metamorphic conditions of anphibolite facies grade. Their kinematic indicators show a mass transport towards east-southeast. The second tectonic event, on the other hand, is characterized by brittle transcurrent faults, with sinistral sense, and metamorphic conditions between greenschist- and prehnite-pumpellyite facies grade. On the basis of lithologic, metamorphic and structural data the following hypothesis is put foward for the geologic evolution: (i) The Campos Gerais belt is the southern extention of the Slo Francisco Craton, whereas the Petúnia Complex is correlated with the base of the Andrelândia GrouPi (ii) secondly, there might have been an oblique collision between two tectonic blocks during the Brasiliano event, with mass transport from W-NW to E-SE, obduction of an ophiolitic sequence, and mixing of lithologies from both terrains. The two last features characterize the "suture zone" between a cratonic block (Slo Francisco Craton) and a mobile belt (Alto Rio Grande mobile belt). This suggests that the boundary of the Alto Rio Grande mobile belt should actually be located further north. The proposed division can also explain the regional distribution of mineral deposits, with massive sulphide deposits concentrated in the greenstone belt sequence of the Campos Gerais belt, and gold and chromium in ophiolitic rocks of the Petúnia Complexo

ASSUNTO(S)

geologia - minas gerais geologia estrutural

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