Geologia, geoquímica e geocronologia da Região de Nova Prata, Dianópolis - TO: Terreno Almas-Dianópolis, Faixa Brasília Setentrional

Abstract

The research presents new geological and structural data, in 25.000 scale, besides geochemistry and geochronology data of the Nova Prata target, located south of the Almas town, SE of Tocantins State. The region was prospect for gold, and several mines were described. In the geotectonic context is located in the NE segment of the Internal Domain of the Brasília belt, made up by Paleoproterozoic to Mesoproterozoic basement associations. In target area, seven lithological units were mapped in detail: two associations of orthogneisses, phyllonitic rocks, muscovite chlorite schists, greenschists, leucogranite and andesite-diorite bodies. The structural analysis resulted on the characterization of ductile phases including the Dn + Dn+1 main phases with the development of the main foliation and the stretching lineation, the Dn+2 late folding, besides and brittle structures as faults and fractures. Based on geometry, two structural domains separated by an oblique NE-SW fault, with reverse and dextral components, were characterized. Two generations of quartz veins were identified, the fist one parallel to the main foliation and related to the metamorphism, and the late one with irregular distribution. The southern domain is dominated by a penetrative N-S trending foliation, while the Northern domain is marked by a NE-SW foliation, discrete thrust shear zones and tight to open folds. Geochemical data suggest cordilleran arc-related to collision orogenic environments. New LA-ICPMS U-Pb data detected two magmatic pulses: the older one is represented by the southern orthogneisses with crystallization ages of ca. 2,46Ga, while the youngest one is defined by the ca. 2.2 Ga orthogneisses of the northern segment, that also display inherited zircons of the same age of the oldest group. Sm-Nd isotopic data for both the orthogneisses and diorite–andesite dykes point out the cordilleran setting, with reworking of older crustal rocks and some juvenile contribution, as suggested by weakly negative and positive εNd values