PETROGRAPHIC DESCRIPTION OF THE MAFIC AND ULTRAMAFIC ROCKS OF THE OURO FINO UNIT, NOVA LIMA GROUP, IN CAETÉ AND SANTA BÁRBARA, MG

Abstract

The petrographic study of rocks of Ouro Fino unit’s Nova Lima group, Greenstone Belt Rio das Velhas, on interior of Quadrilatero Ferrifero, cointains few affected samples by alterations processes. Many rocks have the primary features like lavas in pillow, tonsils and pox. The petrographic analysis classifies the rocks in tholeiitic basalt and magnesium tholeiite. Unidade Ouro Fino’s metabasalts are from ocean bottom ambiente shown by structures (pillow lava) and lithologic associations (banded iron formation and metachert). A few minerals was recognized in petrographic thin section allowing the description of its mineral paragenese and a needed classification.The geochemical characteristics consulted in the literature indicate that part of the metabasalts was formed by a mantle plume (P-MORB). These characteristics infer a submarine plateau ambient.