Caracterização geológica de granitoide no Distrito de Gonçalves, município de Monte Carmelo - MG

Abstract

The region of this study is inserted in the southern domain of the Brasília Belt, from which the geological mapping and petrographic characterization of the rocks that define a granitoid of elongated shape in NS direction, belonging to the Monte Carmelo Complex (CMC) and are located northeast of the district of Gonçalves - MG. The igneous body belonging to the CMC, is Neoproterozoic in age and is intruded into the shale mica of the Araxá Group, where it presents a Granodioritic Facies and an Association of Monzogranitic Facies made up of gray and pink colored rocks. All facies present equigranular textures and homogeneity in composition and preserved igneous textures, suggesting that despite the fractionation with the formation of three distinct facies, the cooling of the magma occurred as a continuous process. They are rocks with hypidiomorphic textures and peraluminous character, which have preserved magmatic textures (graphic, pertitic and mymequitic) and differences in mineralogical percentages and alteration processes. Granodiorite has paragenesis with a higher volume of oligoclase and smaller microcline compared to monzogranite, in addition to quartz, biotite and muscovite. Micas and pseudomorphs are uncommon, as are accessory minerals apatite, rutile and zircon, with opaque minerals abundant and the epidote the main secondary mineral. The igneous paragenesis of the monzogranitic facies association consists of oligoclase, quartz, microcline, biotite and muscovite, with accessories represented by opaque minerals, apatite, rutile and zircon. The pseudomorphs, chlorite, zoisite and epidote are secondary, the product of the processes of sericitization, saussuritization and chloritization. The gray monzogranite emerges in the southern portion of the granitoid, presents fine granulation and a greater degree of deformation, evidenced by the regional foliation marked by the recrystallization and stretching of the quartz and muscovite crystals, which often present mica fish texture and mark the preferred orientation of the rock, in addition intense plagioclase saussuritization, abundance of pseudomorphs and a smaller volume of biotite compared to pink monzogranite facies. The pink monzogranite has medium granulation and predominates in the northern and southeastern regions of the granitoid, differing from the gray facies in terms of composition and less degree of deformation. The post-magmatic processes are less intense in granodiorite than in monzogranitic facies and cataclastic, milonitic, microfracting, intracrystalline deformation, recrystallization, stretching and mica fish texture have been recognized in all facies and associations, which are associated with mechanisms of brittle-ductile deformation, the mica fish texture being related to shear features. Magmatic crystallization presents evidence of the formation of magmatism in pre- to sin-collisional conditions, evidenced by the regional deformation imposed on these rocks, followed by the formation of post-magmatic micas, marked by the absence of deformational features. Sericitization, saussuritization and chloritization suggest that metamorphism is of shale-green facies, with temperatures in the range of 200-300 ° C. The regional tectonics is responsible for the deformation that affects the granitoid, which is not homogeneous and acts with different deformation rates and is concentrated in the southwest part of the body, where the deformation generates a penetrative low-angle foliation in the gray monzogranite.