Metasomatic evolution of granites, northeast Minas Gerais, Brazil

Geological mapping, petrographic, geochemical (major, trace elements and REE), and fluid inclusion studies were carried out on some intrusive granites outcropping in lhe Coronel Murta-Rubelita region (Middle Jequitinhonha Valley ), norlheast Minas Gerais State, Brazil. The granites were forcefull emplaced in quartz-mica schists and quartzites that belong to lhe Salinas Group (undifferentiated Proterozoic). Salinas Group underwent a Barrowian type metamorphism at about 650 Ma in lhe domain of lhe Aracuai Foldbelt. The granitic plutons were characterized as post-tectonic intrusions (525 ± 30 Ma) that clearly disturbed the large open folds of lhe last regional deformation phase. The main granitic types recognized are: biotite granite, biotite (-muscovite) granite, muscovite (-biotite) granite, pegmatoid granite and rnuscovite-tourmaline or albite-tourmaline granite, Granites s.s. are largely dominant over granodiorites. The granites are alkaline, K-rich, and metaluminous (biotite granite) to peraluminous (other types). Biotite granite appears to be more representative of lhe original anatetic liquid while the other types, excepted lhe pegmatoid granite, are metasomatic facies wilhin each intrusion. Silicated residues of lhe granitic melt were crystallized along lhe cupolas of some plutons, yielding a thin cap of pegmatoid granite. An evolution model for the granites is outlined. The sequence of lhe granitic facies wilhin the plutons starting from their bottom and inner parts (cores) to their rims and cupolas is exemplified in the sucession of biotite granite, biotite (-muscovite) granite, muscovite (-biotite) granite, muscovite granitoids more or less albitized and/or tourmalinized and pegmatoid granite. This sequence also defines the path of the metasomatic fluids.