Geochemistry of the Glória Quartz-Monzodiorite: Implications for Paleoproterozoic Evolution of the Southern Sector of the Mineiro Belt, Minas Gerais State, Brazil

Abstract

The Glória quartz-monzodiorite originated at 2188 ± 29 Ma ago in the central segment of the Paleoproterozoic Mineiro belt is intrusive into the Rio das Mortes greenstone belt. Most of the major, minor and trace elements have not been extensively modified during the regional metamorphism. The Glória quartz-monzodiorite shows a calc-alkaline, metaluminous, arc-related geochemical signature, and displays major and minor trace element differences among the recognized fine, fine/medium and medium-grained facies. The medium-grained facies rocks show SiO2 variation (from 58.2% to 64.3%) that allows subdivision into two sub-facies (medium I and II). The REE contents of the fine/medium and medium-grained sub-facies I show prominent LREE enrichment ([La/Yb]N between 29.7 and 38.0) and weak negative Eu anomalies. Geochemical modeling and trace element ratios support that the chemical differences resulted from progressive fractional crystallization of amphibole in fine, fine/medium and medium I sub-facies and plagioclase in medium II sub-facies. Overall field observations, geochemistry and age determinations of coeval Paleoproterozoic plutons in the region between Lavras and São João del Rei cities indicate that the Glória quartz-monzodiorite represents the old body of the pre-collisional phase of the Mineiro belt.