Petrography and geochemistry of the Pedra Dourada Granulite, southeastern Minas Gerais, Brazil

Abstract

The Pedra Dourada Granulite (PDG) occurs at the southeastern portion of the Aracuai Belt, north of the town of Ponte Nova. It comprises bodies up to 45 km2 inserted into amphibolite-facies gneisses of the Mantiqueira Complex. Motivated by the discrepancy of metamorphic grade with surrounding rocks, this paper presents results of the petrographic and geochemical investigation of the PDG. The unit is comprised of meta-igneous and metasedimentary rocks. Meta-igneous rocks dominate and include felsic granulites (biotite ± garnet-bearing and orthopyroxene-bearing) and subordinate mafic granulites. Metasedimentary rocks are aluminous granulites with Al-rich mineral assemblages (garnet, sillimanite, spinel). Geochemical data show that most of felsic protoliths are peraluminous rocks including granites, granodiorites and diorites of calc-alkaline character, chemically similar to granitoids of convergent tectonic settings. Mafic protoliths are metaluminous rocks comprised of gabbros and subordinate diorites of tholeiitic affinity, compositionally similar to plate margin basalts. Aluminous protoliths may be peraluminous pelitic rocks and wackes, analogous to sediments from convergent environments. The mineral assemblages indicate that these rocks were metamorphosed under medium-P granulite-facies conditions. Coronitic garnet textures suggest a near-isobaric cooling (IBC-path) after metamorphic peak.