Petrology and geochemistry of mafic-ultramafic rocks from selected areas: tectonic and metallogenetic implications

Abstract

The project is part of a research on mafic-ultramaficrocks which has been performed during the last four decades. The present study refers to four main types of mafic and ultramafic rock associations: the mafic dykes from the cratonic areas of the South American Platform, mainly those from the Amazonian Craton, the large mafic-ultramafic stratiform complexes of Niquelândia and Cana Brava, in Goiás State, the basalts and alkaline rocks form the Paraná-Etendeka system, in South America, Namibia and Angola, and the ultramafic-alkaline rocks of Planalto da Serra in the Amazonian Craton. Age determinations of mafic dykes can also generate important data on mantle composition and on the tectonic evolution of continental areas during the geological times. In several regions of the world, they are related to the breakdown of nontinents and supercontinents. Similar geochemical and tectonic importance is attributed to the study of the Mesozoic volcanism of the Paraná-Etedenka system, and its relationship with the opening of the South Atlantic Ocean. The studies on the age, stratigraphy and evolution of the stratiform complexes of Niquelândia and Cana Brava, important sources of nickel and asbestos respectively, are controversial with respect to their ages, stratigraphy and tectonic evolution. The alkaline ultramafic rocks from Planalto da Serra, in the Mato Grosso State, have been recently discovered, and their age, petrology and tectonic role are poorly known. (AU)