Mapeamento geológico e análise estrutural do setor noroeste do complexo Abadia dos Dourados, Orógeno Brasília Meridional

Abstract

The city of Abadia dos Dourados, located in the macroregion of Alto Paranaíba, in Minas Gerais, present occurrences of Meso and Neoproterozoic rocks belonging to the internal domain of the southern sector of the Brasília Orogen. This geotectonic unit composes the Tocantins Province, a large diachronic orogenic system developed in the Brasiliano Cycle by the amalgamation of West Gondwana. The present study focuses on the tectonostratigraphic characterization of the northwestern sector of the Abadia dos Dourados Complex, a volcanosedimentary sequence that is composed of mafic and acid metavolcanic rocks, chemical and siliciclastic metasediments. For this purpose, geological mapping, structural and petrographic analysis were carried out at a scale of 1:25.000. In the present work, the Abadia dos Dourados Complex was subdivided into the Lower Unit, composed of plagioclasequartzsericite phyllites, defined as acid metavolcanic rocks, amphibolites and magnetitehematite quartzites; and the Upper Unit, which presents sericite phyllites, garnetsericite phyllites and quartzites. Muscovite schists and garnetmuscovite schists associated with the Araxá Group were also described. Two deformation phases responsible for the structuring of the area were defined. Phase D1 was generated by means of a NESW tectonic shortening, being subdivided in two moments: the first one, responsible for the generation of F1a folds, stratigraphy inversion and generation of the first metamorphic foliation S1a, and its parallelism with the compositional layering S0; and a second moment, marked by the generation of F1b folds, of the second metamorphic foliation S1b, of mylonitic foliation Sm, Lb1 intersection lineations, Lx streth mineral lineations and thrusts with vergence to NE. Phase D2 marks a tectonic shortening of NWSE direction, which generated F2 folds, the S2 metamorphic foliation, Lb2 intersection lineations and the main fractures in the area. The mineral assemblages and structures described indicate that the rocks in the area were metamorphosed into the greenschist facies, zones of chlorite, biotite and garnet. The metamorphic peak occurred in phase D1, between the generation of foliations S1a and S1b. Phase D2 presents itself as postmetamorphic. The contact relations observed among the lithologies are generally depositional, with the exception of the thrust faults without regional expression within the complex and the thrust fault that places the metasediments of the Superior Unit over the metasediments of the Araxá Group in the northeastern sector of the area. The stratigraphic column interpreted in this work indicates a succession of metasedimentary rocks overlying metavolcanic rocks, organized from bottom to top as follows: the base consists of plagioclasequartzsericite phyllite (acid metavolcanic) intercalated to magnetitehematite quartzite, overlain by amphibolite, the intermediate section presents sericite phyllite with intercalations of garnetsericite phyllite and quartzite, and the upper part is composed of muscovite schist with intercalations of garnetmuscovite schist, and amphibolite.