DIATEXITIC GNEISSES OF THE ANDRELÂNDIA GROUP, SOUTHERN MINAS GERAIS, BRAZIL: GEOLOGICAL AND GEOCHEMICAL CONSTRAINTS

Abstract

The basal unit of the Andrelândia Group underwent barrovian metamorphism that formed stromatic biotite metatexitic gneiss grading to (garnet)-biotite-muscovite granitic diatexitic leucogneiss. The anatectic trend culminated with the formation of late-to post-tectonic (garnet)-(tourmaline)-biotite-muscovite intrusive leucogranite. The diatexites are hololeucocratic to leucocratic rocks and vary from syenogranite to granodiorite with biotite, muscovite, epidote, allanite, zircon, apatite, sphene and rare monazite and garnet. The geochemical behavior points towards a peraluminous restrict calc-alkalic sequence (69% to 75% SiO 2), with discrete major and some trace elements content variations. The observed Ba, Sr, Y, Zr, and mainly REE-contents oscillations define three different groups. The accessory mineralogy of the diatexites is responsible for the discrimination of these groups.