Química mineral de anfibólio e piroxênio dos vulcanitos intermediários paleoproterozóicos da região de São Félix do Xingu (PA), Província Mineral de Carajás

Abstract

In the São Félix do Xingu (PA) region, Amazonian Craton, there is widespread Paleoproterozoic effusive and explosive volcano–plutonism, grouped in Sobreiro and Santa Rosa formations. EMP analyzes performed in clinopyroxene, amphibole, and plagioclase phenocrysts of the Sobreiro Formation; and feldspars in the Santa Rosa Formation rock types suggest important isomorphic cationic substitutions in these phases. The clinopyroxene is augite with minor diopside component and reveals jadeite exchange. The amphibole is predominantly as magnesiohastingsite and has highly oxidizing state. Edenite and Tschermaks exchanges are observed in this phase. Feldspars from the Sobreiro Formation have wide variation in its composition, both in lava flow and volcaniclastic facies. In the Santa Rosa Formation feldspars are commonly more evolved. The data obtained in this study integrated with geochemical constraints support the indication that the Sobreiro and Santa Rosa formations evolved under the combined influence of crustal assimilation and fractional crystallization.