AGES OF GRANITES OF THE SERRINHA NUCLEUS, BAHIA (BRAZIL): AN OVERVIEW

Abstract

The ages of granites of the Serrinha Nucleus (SN), in the eastern part of Bahia State, Brazil are poorly constrained and radiometric dating is mainly by the Rb-Sr whole rock isochron method, indicating a complex intrusive history. New Pb-Pb and U-Pb zircon for plutons widely distributed within the SN terrains range from Archean (>3070 Ma) to Paleoproterozoic (2067 Ma) and generally support the interpretation that at least three plutonic events affect these terrains. The range of ages evidently constitutes a large interval of regional granitic emplacement which can be divided into three principal domains: pre, syn and late/post tectonic. The new Archean ages (2.7 to 3.1 Ga.) by the U-Pb zircon method indicate reworking of an older crust during the Paleoproterozoic plutonic event in the SN region and clearly point to the existence of an Archean basement prior to 2.7 Ga. (Jequié Cycle). The younger ages (table 1) help to further constrain the extension and age of Archean components of the São Francisco Craton which is important for a complete understanding of the Precambrian geology of that part of Brazil.