Idades U-Pb em zircão de alguns granitos clássicos da Província Borborema

Abstract

The Neoproterozoic evolution of the Borborema Province in the east-northeast part of the South American platform exhibits remarkable, much studied granitic plutonism. In 1967 F. F. M. Almeida and co-workers discriminated a series of granitic typologies as"Conceição type","Itaporanga type" etc, mostly based upon general geological features and petrographic grounds. This preliminary classification has somehow been maintained in all subsequent papers up to now, despite all the newly observed plutons and the newly generated tectonic, geochemical and isotopic data since then. Samples of these classical types of granites from their type-localities were analyzed geochronologically using the U-Pb method in zircons in response to the felt needs of the geological community, because previous age-determinations involved less accurate methods. The new data have been added to all other preexisting U-Pb data (from other granitic bodies) obtained over the last decade, making it possible to recognize three main stages of granitic magmatism for the Borborema Province: 650 - 625 Ma, 580 - 570 Ma and 545 - 520 Ma. The last group of dates is closely association with the escape tectonics of the Brasiliano-Pan African collage, which preceded the assembly of the supercontinental landmass of Western Gondwana.