Precambrian granitic magmatism in Brazil

Abstract

This article provides an overview on Precambrian granitic rocks of Brazil, highlighting their most outstanding aspects. In the Amazon craton, five groups of Archean granitoids (2.96 to 2.55 Ga) were identified in the Carajás region. Proterozoic A-type and within-plate rapakivi granites are grouped into several age intervals (1.88-0.98 Ga). They are meta- to peraluminous with subordinate peralkalic terms and are tin-mineralized with associated Y, REE, Th, F (cryolite), Zr and Nb. Nine groups of Neoproterozoic granitoids and syenitoids are recognized in the Borborema province, northeastern Brazil, on the basis of mineralogical, geochemical and isotopic features. These characteristics indicate both lateral and vertical differences among the three major domains in this province, which are separated from each other by continental-scale shear zones. Study of calc-alkalic to high-K calc-alkalic magmatic epidote-bearing granitoids, common in this area, yields a preliminary estimate of the speed of magma upward transport and emplacement. The 0.58 Ga-old syenites in the syenitoid line in the Borborema province constitute one of the few Neoproterozoic ultrapotassic plutonic provinces in the world. Granitoids in the Araçuail Coastal foldbelt in eastern Brazil, are deeply exposed together with the roots of a Neoproterozoic mobile belt and recorded several of the evolutionary history of this belt. In central Brazil, the A-type granites of the Goiás tin province, the Neoproterozoic arc granitoids of Mara Rosa and Arenópolis, the Neoproterozoic peraluminous granites of southern Goiás and the late to post-orogenic bimodal magmatism are a proxy for the tectonic evolution of the Brasilia foldbelt. Most Neoproterozoic granitic magmatism in southern Brazil is possibly related to mantle source of the EM1 type.