Petrography and Geochemistry of Metamafic and Metaultramafic Rocks from Cambuci, Rio de Janeiro

Abstract

In the northern Rio de Janeiro State, mafic and ultramafic rocks occur locally showing evidences of metamorphism and deformation. They are (meta)clinopiroxenites, (meta)piroxenites, (meta)diorites to quartzdiorites and mainly (meta)gabbros, (meta)norites and (meta)gabbronorites. The rocks present isotropic to foliated fabric marked by the orientation of piroxene/amphibole and feldspar or even mafic clots. Contrasting with samples that exhibit clear recristalized fabric, primary textures as granular, cumulatic and flow are found in many samples of the different lithotypes. Geochemical studies indicate tholeiitic basaltic composition and ocean floor signature, particularly transitional to enriched MORB. The obtained data allow interpreting these rocks as paleo-ocean remnants tectonically positioned in the regional paragneisses.