Volcanic and volcaniclastic features in archean rocks and their tectonic environments, rio das velhas greenstone belt, quadrilátero ferrífero, mg - brazil

Rocks of Rio das Velhas Greenstone Belt subject of this paper are contained within the Quadrilatero Ferrifero region, Minas Gerais State, in the southeastern portion of Brazil. Volcanic rocks are represented by komatiites, basalts, andesites, dacites and volcaniclastic rocks, metamorphosed under greenschist facies. Despite intense deformation, these rocks preserve some original textural features like spinifex, variolitic, porphyritic and ophitic. Quench textures, pillow lavas and chemical sediments association (iron formation and metachert) indicate an ocean environment for mafic-ultramafic flows. The basalts geochemical patterns indicate that at least part of them formed from a mantle plume. The felsic volcanic and volcaniclastic rocks association indicates a subaerial explosive volcanism in an island-arc type environment.