Mapeamento geológico e petrografia das rochas do grupo Araxá na bacia do rio preto, Abadia dos Dourados (MG)

Abstract

Geological mapping and petrography are important methods for understanding the lithostratigraphic arrangement and geological history of a given region. To understand the lithostratigraphy and the structural and metamorphic evolution of the region of the present study, a detailed geological mapping (1:25.000) and analysis petrographic blades were performed. The study area is located in the municipality of Abadia dos Dourados (MG) and includes rocks of the Araxá Group and Abadia dos Dourados Complex, which make up the inner portion of the Southern Brasília Belt, Tocantins Province. The detailing of this work allowed for the description and individualization of five lithological units characterized as Biotite-muscovite schist, Biotite-garnet-muscovite schist and Biotite-muscovite granite associated to Araxá Group; phyllite associated to Abadia dos Dourados Complex; and the Rio Preto Metatexite Migmatite unit. This work allowed the identification of granite and migmatite bodies that until now had not been characterized in the area covered by this work. In the metamorphic rocks associated to migmatization, a metamorphic peak was characterized in the amphibolite facies and partial fusion in pressure and temperature conditions above 10 kbar and 700° C. For the metasedimentary rocks the metamorphic peak is attributed to the staurolite zone with the paragenesis staurolite + garnet + biotite + muscovite + quartz. All lithotypes were affected by a retrometamorphism in the greenschist facies characterized mainly by saussuritization present in the migmatites and substitution of high grade minerals for lower metamorphic grade minerals in the metasedimentary rocks. Two deformational phases were defined: D1 and D2. D1 is subdivided into early and late stages, both marked by compressional stress in the NE-SW direction, the first stage is related to the generation of the F1 recumbent folds responsible for the formation of the S1 foliation parallel to the compositional bedding S0, the late D1 stage is associated with the generation of the F1' folds, responsible for the formation of the S1' foliation, Lb1 intersection lineation, Sm milonite foliation and a Lm stellate lineation associated with Sm. D2 represents the compressive tectonic stress in the NW-SE direction responsible for the generation of the F2 folds, formation of the S2 foliation and Lb2 intersection lineation, this stage is also responsible for the generation of the brittle structures.