Petrography and chemistry of Aripuanã Granite, southern Amazonian Craton

Abstract

The term Aripuanã Granite refers to a group of undeformed circumscribed granitic bodies, intrusive in the Roosevelt Group’s metavulcanosedimentary sequence, recognized in the southern portion of the Amazonian Craton. The main granitic body constitutes in an oval batholith with a diameter of less than 15 km, which occurs in the north of the Aripuanã city, in northwestern Mato Grosso. It consists of thick porphyritic hornblende-biotite syeno to monzogranites, of gray or red coloration and locally with rapakivi textures. In the marginal areas a grain size reduction of the porphyritic features with predominance of a fine equigranular facies associated to fast cooling is observed. The common late facies consist of equigranular dykes of gray color, pink and gray aplites and pegmatitic veins. Post-magmatic veins of quartz, fluorite, and muscovite occur in areas of brittle deformation where the rocks show intense hydrothermal alteration. This hydrothermalism heterogeneously affects the country and the magmatic rocks, facilitating the circulation of fluids and favoring the concentration of disseminated zinc sulphides, always related to late fracturing. The granites host country rocks, granodiorites, quartz diorites and micaceous rocks xenoliths. At the edges, there are veins and granitic apophyses, as well as contact metamorphism in the host rocks. The monzogranites are peraluminous and belong to the high potassium to shoshonite series, similar to ferroan granites, type A, post-collisional to anorogenic and associated to Jamari Magmatic Arc evolution.