Geologia, petrografia e geoquímica das rochas vulcânicas Uatumã na área sul de São Félix do Xingu (PA), Província Carajás

Abstract

The volcanic rocks southern São Félix do Xingu, Pará state, north Brazil, are geologically inserted in the geochronologic Amazonia Central province, southeastern Amazonian craton. These rocks are dominantly related to the Sobreiro Formation, and to the Santa Rosa Formation, both belonging to the Paleoproterozoic Uatumã group. Three facies of the Sobreiro Formation had been identified in this work: subaerial lava flow of subalkaline facies; subaerial lava flow of calc-alkaline to shoshonitic facies; subaerial volcaniclastic facies. The samples of the Santa Rosa Formation are subaerial lava flow. The Sobreiro Formation consists of basaltic andesite, andesite, traquiandesite, traquite, crystal tuffs, lapili-tuffs and polymictic breccias. The lithotypes of the Santa Rosa Formation are rhyolites. Rocks of the Sobreiro Formation have contents of SiO2 between 52.14 and 69.21% (wt%) and K2O/Na2O ratios between 0.16 and 1.62. The Santa Rosa Formation form an evolved series with SiO2 contents between 72.27 and 77.14% (wt%) and K2O/Na2O ratios between 1.50 and 2.12. The Sobreiro Formation is mainly calc-alkaline, weakly transitional calc-alkaline to shoshonitic, has metaluminous to weakly peraluminous composition and tectonic signature of volcanic arc environment. The Santa Rosa Formation has peraluminous to weakly metaluminous composition and A-type signature with intraplate tectonic affinity. The volcanic rocks of the southern area have perfect correlation petrographic, geochemical and tectonic volcanites with the area west/southwest of São Félix do Xingu.