Brasiliano-age granitoids in the Sergipana Fold Belt, NE Brazil: the Coronel João Sá Pluton

Abstract

The Coronel João Sá pluton is a zoned Brasiliano-age, late- to post-tectonic intrusion in the Macururé schist domain of the Sergipana Foldbelt, Northeast Brazil. Biotite-hornblende granodiorite predominates, and flattened ultramafic to intermediate enclaves are present. Igneous orientations are present but fabrics produced by strong solid-state flattening are absent. Rb-Sr whole rock isochrons including enclaves and their host rocks yielded a probable intrusion age of 614 Ma which dates the waning phase of the dominant deformation which produced the F2 foliation of the Sergipana belt and is close to ages reported for late tectonic granites in other Brasiliano domains of Northeast Brazil. More radiogenic Sr (ISr(614) = 0.71008 ± 52) is present in some felsic rocks, while less radiogenic Sr (ISr(614) = 0.70814 ± 18) is mainly found in the more mafic core of the main body. Sr isotopic equilibrium between most enclaves and their host rocks was attained. Textural evidence, especially in the enclaves, shows that magma mixing occurred, but late biotite formation in the enclaves caused modifications of their chemical compositions. The geological, petrographical and isotopic evidence shows that the pluton was probably fed by a complex feeder system into the crust under extensional conditions. Variable upper crustal contamination was probably responsible for the isotopic heterogeneity of Sr.