Petrografia dos enclaves máficos dos granitoides e gnaisses aflorantes na Vila Cruzeiro do Sul, porção sul do domínio de Bacajá

Abstract

Mafic enclaves are typical feature of Novolândia granulites and Cajazeiras complex, Cruzeiro do Sul village, southern portion of Bacajá domain. These bodies exhibit different shape, are more abundant and larger when hosted in the Novolândia Granulite. When the units are far of shear zone, the enclaves are angular and show reaction rim. Whereas, in shear zone, the enclaves display flatted, boudins and/or augen shape, sometime crosscut by quartz-feldspar veins. On the basis of textural aspects and mineralogical contents (plagioclase+amphibole, biotite+amphibole/others mineral, amphibole/ others mineral and clinopyroxene+orthopiroxene/amphibole+biotite), the enclaves were classified in granulite and amphibolite, and informally as transicional amphibolite. The texture is dominantly granoblastic, and sometime nematoblastic. Furthermore, in transicional amphibolte occur mineral segregation characterized by layering of felsic and mafic minerals. The corona texture is common, being characterized by pyroxene cores surrounded by amphibole, in the case of granulites and transitional amphibolites, pyroxene is bordered by reddish-colored biotite. The corona textures suggest that probably part of the amphibole and biotite were originated from the hydration process of pyroxenes in retrometetamorphism conditions. Two hypotheses were discussed in this work: (a) the enclaves as remnant fragments of oceanic crust; (B) enclaves from intrusive mafic bodies.