Petrografia, Litoquímica e Geocronologia (U-Pb) das rochas hipabissais do Granito São Vicente na região do Parque Estadual Águas Quentes, Mato Grosso

Abstract

The petrogenesis of the hypabissal rocks of the São Vicente Granite on the region of the Águas Quentes State Park, south-central region of Mato Grosso state, allowed the recognition and characterization of distinct facies for the granite main body. The petrographic procedure allowed the recognition of four genetic and petrographical facies: coarse syenogranite consisting of leucocratic, equigranular and locally inequigranular rocks; porphyritic aplite composed of leucocratic fine to medium grained inequigranular rocks of syenogranitic composition; microgranite with microporphyritic texture and microphenocrysts within a very fine grained quartz-feldspatic groundmass and recurrent micrographic texture; and porphyritic rhyolite, confined to the Águas Quentes State Park balneary, consisting of a porphyritic to glomeroporphyritic rock with a very fined to aphanitic groundmass, characteristics of hypabyssal intrusions. This facies association suggests that the study area represent a cupola level of an epizonal intrusion. The distribution pattern of rare earth elements points to a strong fractionation of LREE, with average of LaN/SmN ratios of 7.87, negative Eu anomaly (Eu/Eu* ~0.38) and enrichment of HREE established by GdN/YbN 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 aplite facies. U-Pb Shrimp dating yield and age of 528±4 Ma to the porphyritic rhyolite, assumed as the crystallization age. Thereafter, is suggested that the magma source of plutonic and volcanic rocks of São Vicente Granite on the Águas Quentes State Park region could be derived from subduction related lithospheric sources mixed with deeper asthenospheric sources.