Petrografia e litoquímica de diques máficos mesozoicos e cambrianos (?) de Minas Gerais: comparações com basaltos da província Paraná - Etendeka e com diques da suíte fundão

Abstract

Minas Gerais (MG) keeps several generations of mafic dykes, dating from the Paleoproterozoic to the Cretaceous. From Cretaceous, there are the Transminas and Serra do Mar dyke swarms, and also there are possible representatives of the Cambrian, termed Fundão Suite, which is already described in Espírito Santo (ES). Macroscopically, all of those rocks are similar to each other being fine-grained grey dolerites. Microscopically, all of those rocks show subophitic texture. However, cretaceous dykes are olivine gabbros/olivine basalts and Cambrian dykes are gabbro norites. Lithochemically, all of these dykes are tholeiitic basalts with some degree of crustal contamination, and the Cretaceous are high Ti and the Cambrian are low Ti. Only two dykes belonging to the Serra do Mar swarm are alkaline trachybasaltic andesites. The spidergrams of incompatible and rare earth elements of the Cretaceous dykes show similarities with basalts of the Paraná-Etendeka province, following the OIB pattern, typical of mantle plumes. The Cretaceous dykes of MG correlate geochronologically, petrographic and lithochemically to the basalts of Paraná-Etendeka province. This Cretaceous magmatism derived from a garnet lherzolite source, related to the geodynamic context possibly linked to the activity of Tristan da Cunha mantle plume. The Cambrian dykes, both in MG and in ES, are petrographic and lithochemically similar to each other and show a signature of enriched ocean ridge basalts. Dykes of the Fundão Suite derived from a spinel lherzolite source and are related to the gravitational collapse of Araçuaí Orogen.