The Precambrian geology of the “Borborema”-Belt (States of Paraíba and Rio Grande do Norte; northeastern Brazil) and the origin of its mineral provinces

Abstract

In the crystalline area of the “Borborema” in NE Brazil the final geologic event was a strong static recrystallization, which is manifest in regional granitization, hybride granite, or pegmatite veins. The manifestation varies within the mapped area, it depends on lithology, thickness and structure of the Precambrian metasediments. The age of this phase is between 550 and 450 M. years. Recrystallization is accompanied by weak folding of pre-existing anticlines as indicated by the structural control of the Borborema pegmatites. The principal phase of deformation and the accompanying regional metamorphism are considered to be older, approximately 850 M. years or more. This older regional metamorphism produced rocks of the almandine-staurolite subfacies of the amphibolite facies; locally higher (cordierite and sillimanite subfacies) or lower (greenschist facies) degree of metamorphism occurs. The pyroxene-hornfels facies, which is found in the contact aureoles of hybride granites, occurs exclusively in the tactites (metamorphic dolomitic marls). In clastic metasediments, high grade metamorphic facies is restricted to the contact aureole of a small hypersthene diorite stock.