Petrografia, geoquímica e geocronologia dos granitos Presidente Kennedy e Barrolândia, noroeste do Tocantins – Cinturão Araguaia

Abstract

Several granitic bodies at the eastern of the Araguaia Belt in their area of higher metamorphic grade (Estrondo Group). These granites have been interpreted as positioning to late syn-kinematic in relation to major tectonic during regional metamorphism around 550 Ma. In this dissertation we studied two bodies, the Presidente Kennedy and Barrolândia granites, the latter still unknown in the literature. The studies involved geological mapping of two areas of occurrence of these granites, petrographic analysis, geochemistry and geochronology. The President Kennedy Granite located 6 km northwest of Presidente Kennedy city, comprising a stock of elliptical form, covering an outcrop area whose diameters are approximately 10 km and less than 5 km, intrusive in micaschists of Estrondo Group. The body has well-marked foliation on the edge, although there is a diffuse orientation or even noticeable, as they make a shift to the center of the body. The foliation is accused of everything for the orientation of micas. Petrography, the Presidente Kennedy granite varies from granodiorite to monzogranite compositions, hololeucocratic (M<6) of slightly pinkish gray. Show hypidiomorphic to allotriomorphic texture and medium granulation. They consist mainly of plagioclase (An23-29), quartz and microcline, and minor biotite and muscovite. Apatite, zircon, titanite and opaque minerals make up the accessory, whereas chlorite, sericite, carbonate, muscovite and clay minerals are secondary phases. The Barrolândia Granite surfaces in two distinct parts: (1) 20 km northwest and (2) 10 km southwest of the Barrolândia city, stocks are slightly oval, with approximate dimensions of 7 km, intrusive of Estrondo Group. The body has well-marked foliation on the edge that coincides with the regional foliation. This foliation evidenced by the orientation of micas. Petrographically, the granite and monzogranite are hololeucocratic (M<10) and gray colored. Show hypidiomorphic and allotriomorphic texture the medium granulation. They consist essentially of microcline, plagioclase (An15-20) and quartz and minor biotite and muscovite. Apatite, zircon and opaque minerals make up the accessory mineralogy, whereas chlorite, sericite, muscovite and clay minerals are secondary phases. Geochemical data show that the granites show similarities, have peraluminous character, comprising higher SiO2, Al2O3, K2O and Na2O, and depleted in MgO, TiO2 and Fe2O3Total. Geochronologic analysis by evaporation Pb-Pb zircon method gave age of 539 ± 5 Ma, interpreted as the minimum age of zircon crystallization and hence Presidente Kennedy Granite. The same Geochronologic analysis was conducted in the Barrolândia Granite however the analytical responses were not satisfactory for the age calculation, requiring additional work. The petrography, geochemistry and geochronology of Presidente Kennedy and Barrolândia granites revealed similarities between these two bodies and with other granites that occur in the Araguaia belt. The Presidente Kennedy granite coincide within the limits of analytical error obtained in Santa Luzia Granite (528 ± 5 Ma) and Ramal do Lontra Granite (549 ± 5 Ma) that are correlated to the same magmatic event of the Araguaia Belt. From the geochemical date of the studied granites, reveals very similar signature to the others. In general, the granites are rich in SiO2, and low in MgO, TiO2, and CaO Fe2O3Total, which indicate that it is little fractionated magma and granitic reflect the nature of them.