Mapeamento geológico e petrografia do granito douradoquara, Douradoquara - MG

Abstract

In the surroundings of the municipality of Douradoquara (MG), located in the Triângulo Mineiro region, Neoproterozoic metasedimentary and metamafic rocks of the Araxá Group occur, as well as granitoids associated with the Monte Carmelo Complex. These lithologies are inserted in the southern sector of the Brasília Fold Belt and are related to a syn-tectonic event responsible for the intrusion of granitoids along regional foliations and shear zones developed within the schists. The Douradoquara Granite is located west of the municipality of Douradoquara, Minas Gerais, and was previously mapped by CODEMIG (Catalão Sheet – SE.23-Y-A-I, 2017) at a 1:100,000 scale. The present study aimed to map this granitic body at a 1:30,000 scale, seeking a higher level of detail, as well as the individualization and characterization of its facies based on textural, compositional, and structural variations. The applied methodology was divided into three stages. The pre-field stage consisted of bibliographic review, satellite image analysis, interpretation and processing of aerogeophysical image data, and interpretation of structural lineaments, allowing the preliminary delimitation of zones with similar geomorphological and structural characteristics. The field stage involved geological mapping of the outcropping lithotypes, distinguished based on textural, mineralogical, and structural criteria, in addition to photographic documentation and sample collection. Finally, the post-field stage comprised macroscopic and microscopic analyses of the samples, enabling their classification and differentiation into facies, culminating in the elaboration of a new geological map with redefined limits of the granitic body. The results indicate that the area corresponding to the Douradoquara Granite unit is smaller than that presented in the regional 1:100,000-scale mapping by CODEMIG, with a greater predominance of metasedimentary and metamafic host rocks of the Araxá Group, mainly represented by garnet-bearing quartz–muscovite–biotite schist and amphibolites occurring as lenses with a NW–SE trend. The granitoids are foliated, with preferential orientation according to the regional NW–SE trend. The essential mineralogy consists of quartz, microcline, oligoclase, biotite, muscovite, and garnet, allowing the classification of the lithotypes as inequigranular monzogranites to granodiorites. Based on differences in color and mineralogical composition, the body was subdivided into two facies: inequigranular gray facies and inequigranular whitishgray facies, with their main distinction related to the presence of primary muscovite in the inequigranular whitish-gray facies. The presence of aluminous minerals, such as garnet and primary muscovite, indicates that the Douradoquara Granite resulted from crustal melting, characterizing it as a peraluminous S-type granite. The occurrence of quartz-feldspathic pockets within the foliation of garnet-bearing quartz–biotite–muscovite schist and the magmatic foliation with a regional NW–SE trend evidence its syn-tectonic emplacement, strongly controlled by the structural framework of the host rocks, reflecting the exploitation of these structures during intrusion, as well as the deformational processes active during the Neoproterozoic evolution of the Brasília Fold Belt