GRANITÓIDES SANTA LUZIA: REGISTRO DO MAGMATISMO GRANÍTICO BRASILIANO DO CINTURÃO ARAGUAIA NA REGIÃO DE PARAÍSO DO TOCANTINS (TO)

Abstract

The Brasiliano granitic magmatism of the Araguaia Belt is expressed, from Xambioa region southwards, by a few isolated stocks (Ramal do Lontra granite, Presidente Kennedy granodiorite) that have been emplaced along the eastern margin of this megastructure. However, in the Paraiso do Tocantins region, the Brasiliano granite bodies appear to be much more abundant and constitute the informally denominated Santa Luzia Granitoids. They occur mainly as small stocks, dykes, veins and lenses intruded into the biotite schist and quartzites of the Estrondo Group (Upper Proterozoic), concordantly or not with the foliation of these metasediments. Such spatial relationship with the host rocks suggests that these granitoids are syn to late-tectonic. Petrographic and geochemical studies revealed that these rocks are peraluminous and consist essentially of granodiorites, monzogranites and pegmatoid granites which possibly resulted from differentiation of a single original magma. K/Rb and Rb/Sr ratios are fairly constant and indicate that Santa Luzia granitoids were originated from weakly fractionated magmas generated within the continental crust. The Ca and Sr contents as well as the 87 Sr/ 86 Sr ratios = 0.707 support this hypothesis and point out the gneissic basement (Colmeia Complex) as the principal source of these magmas. The presence of angular enclaves of schist in the granitoids and the sharp borders of these xenoliths suggest that the supracrustal metasediments contributed only subordinately to the formation of these magmas. Finally, these rocks show a trend similar to that of low Ca granites and plot within the field of the island arc granitoids, but close to the field of syn-collisional granitoids on a Rb-(Y+Nb) diagram. It is concluded that the Santa Luzia granitoids are syn-collisional.