Geology of the Três Figueiras Granite: peraluminous magmatism at 585 Ma in southeastern Dom Feliciano belt

Abstract

The Três Figueiras Granite represents an unique occurrence of peraluminous granite in the southeastern Dom Feliciano Belt. Peraluminous granite may contain important data about the tectonic environment and thermal evolution of an orogenic belt. The main goal of this work is to present the geologic characterization of the Três Figueiras Granite, based on field data, structural geology, petrography, geochemistry and geochronology. The granite is light grey coloured composed of quartz, K-feldspar, plagioclase, muscovite, biotite (M’ 7-10), with garnet, tourmaline, zircon, monazite and apatite as accessory minerals. It is synkinematic to the Arroio Grande Shear Zone, where it develops a mylonitic fabric with subvertical tectonic foliation with dip >70° for SE and a stretching lineation marked by elongated micas and aggregates of quartz and feldspar, both with a N80°E trend dipping 10° ENE. The observed microstructures and textures show deformation temperature of at least 550 °C and dextral kinematic. It is classified as a peraluminous granite with A/CNK content ranging between 1.07 and 1.21 and normative corundum from 1.2 to 3 %. It has high SiO2, Al2O3 and alkalis (K2O + NaO) and low FeO, MgO and TiO2 contents. In Harker diagrams the granite shows negative correlation for most of the major elements in response to the fractional crystallization process. Multi-element diagrams indicate an uniform source for the entire inconset of the analyzed samples. Zircon U-Pb SHRIMP dating yielded an age of 585 ± 16 Ma, interpreted as magmatic crystallization an important record of Neoproterozoic peraluminous magmatism in the southeastern portion of the Eastern Domain of Dom Feliciano Belt.