Petrology, geochemistry and geocronology of the President Kennedy and Barrolândia granites: contextualization in the evolution of Araguaia Belt

Abstract

Several granitic bodies have been identified in the easternmost part of the Araguaia Belt, located in the highest metamorphic grade domain (Estrondo Group). These granites are interpreted as late kinematic in relation to the main tectonic and regional metamorphism in the evolution of this belt, at the end of the Neoproterozoic. The Presidente Kennedy Granodiorite (PKG) and the Barrolândia Granite (BG), cropping out in the central portion of the Araguaia Belt, are plutons of this granitogenesis. PKG and BG are small-elongated stocks concordant with foliation of mica schist and feldspathic schist of the Estrondo Group, without metamorphic thermal contact effects. They are hololeucocratic rocks of granodioritic and monzogranitic composition, containing two micas (biotite and muscovite), and eventually garnet. In general, the granites are grayish-gray, slightly pink, equigranular, with hipidiomorfic or alotriomorfic granular textures. However, tectono-metamorphic features are common. These are the polygonal granoblastic texture and foliation defined by the preferred orientation of micas and quartz and elongated feldspars. Their essential mineralogical constituents are oligoclase, microcline, quartz, biotite and muscovite, and the accessories are zircon, apatite, opaque minerals and, rarely garnet. Lithochemical data indicate the peraluminous character of these granites, and high values of SiO₂, Al2O₃ and alkalis, and low values of MgO, Fe₂O_3T and TiO₂. The presence of normative corundum along with petrographic and geochemical data, allows characterize them as S-type granites. The single zircon Pb-evaporation age of 539 ± 5 Ma for the PKG is interpreted as minimum age of crystallization and crustal emplacement
at the end of Neoproterozoic (Ediacaran).