Diorite and hornblendite enclaves at Sumidouro, RJ, central Ribeira belt

Abstract

Dioritic and hornblenditic enclaves crop out in the southeastern Sumidouro region, Rio de Janeiro State. They are enveloped by tonalitic gneiss of the Rio Negro Complex. In the main occurrence, at Barao de Aquino District, a set of rounded megaenclaves are closely related with the tonalitic gneiss groundmass. Petrographic and geochemical aspects (major, trace and rare earth elements) combined with field relations, support a cumulatic interpretation for the hornblendite. This rock probably evolved by differentiation process from the same parental magma of the diorites. In turn, the tonalitic gneiss shows distinct petrographic and geochemical signature, suggesting a different source