Evolução geológica, estrutural e termotectônica da região entre Ouro Fino e Pouso Alegre, sul de Minas Gerais

• Autor(a) principal: Furtado, Pedro Costa
• Data de Publicação: 2018
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UERJ
• Texto Completo: http://www.bdtd.uerj.br/handle/1/7043
• topic: Geotectonic; Structural Geology; Petrography; Geotectônica; Geologia Estrutural; Petrografia; CNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIA::GEOLOGIA REGIONAL

The study area is located in the S/SW portion of Minas Gerais State Brazil, in the Borda da Mata region, encompassing half of the Borda da Mata and Ipuiuna 1:50 000 geological maps. More specifically, the main target of the study is the region that runs between the Guaxupé and Socorro nappes where Itapira Group rocks (Orosirian and Statherian) and their basement, the Pouso Alegre Complex (Rhyacian), occur. The study area is part of the interference zone between the Brasília and Ribeira belts. It is characterized by the interference from central Ribeira Belt structures into the southern Brasília Belt context. Through geological mapping on a 1:25 000 scale, two distinct lithological domains were recognized. The Inferior domain consists in a metavolcanossedimentary sequence equivalent to the Itapira Group, composed, from base to top of: Metabasic to intermediary rocks (Amphibolite, ultramafic and hornblend-biotite gneiss); Quartz-rich (Garnet) Biotite gneiss with intercalations of amphibolite, gondite and (sillimanite) biotite schist; Quartz-sericite schist/phyllite; (sillimanite) biotite gneiss/schist with intercalations of graphite gneiss and sparse amphibolite and feldspathic quartzite bodies. This sequence lies over ortho-derived rocks of the Pouso Alegre Complex, represented by the migmatitic biotite orthogneiss and porphyritic (hornblend) orthogneiss units. Itapira Group rocks are locally intruded by dikes of a hololeucocratic metagranite, correlatable to the Taguar metagranite (Statherian). The Superior Domain is represented by the Guaxupé (to north) and Socorro (to south) nappes. They are composed of rocks with igneous protoliths, corresponding mainly to (mega)porphyritic orthogneiss of the Pinhal-Ipuiuna and Serra da Água Limpa batoliths of Cryogenian age, with a hololeucocratic charnockitic gneiss on the base. These rocks register three different metamorphic events and at least three ductile deformation phases. The oldest metamorphic stage (M1 Rhyacian/Orosirian limit) is evidenced only on Itapira Group basement rocks, by partial fusion of Pouso Alegre Complex orthogneiss. The main metamorphic event (M2) of the area is preserved on all described units, and unfolded under medium to high amphibolite facies with intermediate pressure, in the sillimanite zone. The M2 event is contemporaneous to the main deformational phase (Dn), which produced isoclinal folds and oblique thrust-related shear zones with ENE vergence. This puts Guaxupé and Socorro nappes rocks over the Itapira Group and Pouso Alegre Complex, and is associated with the collisional stage of the southern portion of the Brasília Belt (Cryogenian/Ediacaran limit). The third metamorphic event is of local influence, and occurs in green schist to low amphibolite facies on the shear zones of the Ouro Fino shear belt. This belt consists in nine E-W to NE-SW oriented shear zones with mainly dextral throw and subordinate transtensive and transpressive domains which connect locally through smaller shear zones, producing a regional anastomosed pattern. Closed to tight folds with subparallel axis, stretching lineations and NW vergence develop associated to the previously described shear zones during deformational phase Dn+1. The Ouro Fino shear belt is the result of a NW-SE compression related to the first collisional stage of the Ribeira Belt (Ediacaran)