GRANULITE/CHARNOCKITE FROM THE JUIZ DE FORA DOMAIN, CENTRAL SEGMENT OF THE BRASILIANO RIBEIRA BELT

BEATRIZ PASCHOAL DUARTE, MONICA HEILBRON, MÁRIO DA COSTA CAMPOS NETO

Resumo


The Ribeira Belt is the product of the last stage of Brasiliano collage in southeastern Brazil. Its Ocidental Terrane comprises the reworked margin of the San Francisco Craton, which is composed by two thrust sheets: the Andrelandia and the Juiz de Fora domains (Heilbron et al. 1998). The latter includes three different tectonically bounded litho-stratigraphic units: pre-1.8 Ga. granulite facies orthogneisses; post-1.8 Ga. metasedimentary rocks; and Brasiliano-Pan-African granitoids and charnockitoids. Each unit comprises a characteristic type of granulite/charnockite. The pre-1.8 Ga. unit is composed of basic to acid orthopyroxene-bearing orthogneisses with a granoblastic fabric. Field and petrological data indicate that granulite metamorphism is the result of infiltration of CO2-rich fluids. A late mylonitic foliation and retrogressive mineral products are contemporaneous to the Brasiliano-Pan-African tectonic stacking. The paragneisses display granulite facies parageneses within a foliated and/or mylonitic structure and show features of in situ migmatization caused by the breakdown of biotite. Charnockite bodies occur as garnet-(orthopyroxene)-bearing leucosomes within the paragneisses and also as isotropic to slightly foliated individualized igneous bodies with enclaves of the other units. They are interpreted as the product of anatexis of the paragneisses with minor contributions of the prthogranulites. Granulite facies metamorphism of the paragneisses, and anhydrous melting were caused by tectonic stacking related to the Brasiliano collage.

Palavras-chave


Precambrian; Ribeira Belt; Granulite; Igneous charnokite.

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