Geology and petrology of the São Vicente Granite in Águas Quentes State Park region, State of Mato Grosso, Brazil

Abstract

The petrogenesis of the hypabissal rocks of São Vicente Granite in Águas Quentes State Park allowed the recognition and characterization of distinct facies. Based on petrography, four isotropic facies were individualized: coarse syenogranite (equigranular to inequigranular texture, leucocratic); porphyritic aplite (fine to medium inequigranular texture with phenocrysts, leucocratic, syenogranitic); microgranite (microporphyritic texture with microphenocrysts in very fine phaneritic groundmass, recurrent micrographic texture, syenogranitic); and porphyritic rhyolite (porphyritic and glomeroporphyritic texture with aphanitic to very fine phaneritic groundmass). The porphyritic aplite and microgranite facies are typical of granitic cupolas of epizonal bodies. The porphyritic rhyolite facies is related to hypabyssal intrusions. The distribution pattern of rare earth elements points to a strong fractionation of REE, with average of La_N/Sm_N ratios of 7.87, negative Eu anomaly (Eu/Eu* ~0.38) and enrichment of REE established by Gd_N/Yb_N ratios lower than the unit (~0.82). The major and trace element distribution on binary diagrams and the negative anomalies on spidergrams indicate fractional crystallization processes of plagioclase, biotite, apatite and zircon to the syenogranite and porphyritic aplite facies. U-Pb SHRIMP dating of the porphyritic rhyolite yielded an age of 528 ± 4 Ma, assumed as the crystallization age. It is suggested that the magma source of the São Vicente Granite plutonic and hypabyssal rocks in Águas Quentes State Park region could be derived from subduction-related lithospheric sources, or crustal melting, with contribution of a deeper asthenospheric source as a second meaningful component.