Abstract
Petrographical and geochemical whole rock data allowed recognition of a bimodal volcanism, which occurs in the Sao Felix do Xingu region, southeast of the Para state, resulting trachybasaltic, basaltic-andesite, trachyandesitic, andesitic, dacitic and trachytic lavas deposits, as well pyroclastic flow represented by glassy and crystal tuffs and polimitic breccias, grouped in the Sobreiro and Iriri formations of the Uatuma Group. The Sobreiro Formation rocks are metaluminous in composition, fall in the field of calc-alkaline transitional from high-K to shoshonitic series and shows geochemical signature of rocks of mature to immature volcanic arc, formed by clinopyroxene, amphibole and plagioclase fractionation. The Iriri Formation rocks are of metaluminous to peraluminous composition, transitional between subalkaline to alkaline series of rocks and present geochemical composition of intraplate magmatism, predominantly formed by feldspars fractionation. The volcanic association from the Sao Felix do Xingu (PA) region was formed between in a latest stage of subduction event and earliest stage of continental rift, related to the taphrogenetic event of 1.88 Ga registered in most Amazonian Craton.
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