The Chemical Composition of Garnet for Sedimentary Provenance Determination, North Coast of Rio de Janeiro State, Brazil

The chemical composition of garnet, together with the analysis of the heavy minerals and their textures, is an important tool for accurate sedimentary provenance studies. The coastal segment of Northern Rio de Janeiro State, limited by the deltas of the Paraíba do Sul and Itabapoana rivers, was studied by chemical analysis of garnet grains by SEM-EDS, together with mineralogy and texture of the heavy minerals assembly. The sediments are angular to subangular, euhedral to subhedral, with well-defined faces, indicating little transportation reworking, and consequently a proximal source area. The garnet grains shows up as irregular and angular fragments and most of them do not have compositional zoning or mineral inclusions. The chemical compositions of the garnet grains are predominantly almandine and pyrope molecules, determining that the sediment main sources are high-grade metamorphic terrains with granitoid and metabasite contributions. Considering the local geology, the most important sources of the sediments are the paragneisses interleaved with amphibolites of the São Fidélis Group, Coastal Domain of the Oriental Terrain of the Ribeira Orogen. Granitoids intrusive into the Coastal Domain are also important source rocks of the studied sediments.