Geologia do granito Boa Esperança, setor Noroeste do complexo Monte Carmelo, Grupiara–MG

Abstract

This study presents the geological characterization of the northwestern portion of the Monte Carmelo Complex (MCC) batholith, located near the municipality of Grupiara (MG), focusing on the individualization and evolutionary understanding of the Boa Esperança Granite. The methodology integrated a bibliographic review, previous geological data compilation, remote sensing using a Digital Elevation Model (DEM), and airborne geophysical mapping based on gamma-ray spectrometry data (individual K, U, and Th channels and RGB ternary composition), in addition to field stages for sample collection and petrographic thin-section analysis. The study area comprises two main lithostratigraphic units: the Araxá Group (approximately 80% of the area), represented by garnet-muscovite-biotite schists with restricted and subordinate amphibolite lenses, and the Monte Carmelo Complex (approximately 20% of the area), composed of granitoid bodies. Based on color, mineralogical, and textural attributes, the Boa Esperança Granite was subdivided into two facies: grayish monzogranite (grayish facies) and whitish monzogranite (whitish facies), with the additional occurrence of a banded gneiss in the area. Mineralogically, the granitic facies and the observed gneiss share a composition of quartz, K-feldspar, plagioclase, biotite, and muscovite, with garnet as a significant accessory mineral. The Boa Esperança Granite also records intense compressive tectonic deformation related to the Brasília Fold Belt, evidenced by intracrystalline plastic deformation features such as undulatory extinction and stretched quartz ribbons, mechanical deformation lamellae and twinning in plagioclase, and core-and-mantle textures in porphyroclasts, displaying a syn-tectonic character. The body exhibits a peraluminous affinity, generated by the anatexis of aluminum-saturated metasedimentary protoliths. Late- to post-magmatic deuterics (hydrolysis) were also identified, marked by widespread and intense sericitization of plagioclase crystals. These results refine the local geological framework and contribute to the understanding of the regional structural and metamorphic compartmentalization of the Internal Zone of the Brasília Belt.