Caracterização petrográfica, microtectônica, geoquímica e geocronológica do Granito Pedra Selada, Visconde de Mauá, RJ

• Autor(a) principal: Simas, Marcela Perroti
• Data de Publicação: 2021
• 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/1/19677
• topic: Granito Pedra Selada; Faixa Ribeira; Faixa Brasília; Zona de Interferência; Idades U-Pb em zircão; Geoquímica; Ribeira belt; Brasília belt; Interference Zone; U-Pb zircon ages; Geochemistry; CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIA

The Pedra Selada Granite (GPS) corresponds to a granitoid body that occurs in the Serra da Pedra Selada region, near the town of Visconde de Mauá (RJ). According to previous works, this body is associated with a I-type syn-collisional porphyritic magmatism identified in the central segment of the Ribeira Belt. However, the studied region has also been correlated to the Interference Zone between the Brasília and Ribeira belts. In order to relate the emplacement of this granitoid with the evolution of the aforementioned belts, a study of the Pedra Selada Granite was carried out via 1:20,000 scale mapping, petrographic, microtectonic, lithogeochemical and geochronological characterization. The data obtained in the field and in petrographic analysis indicate that the granitoid is a generally homogeneous porphyritic rock, presenting K-feldspar megacrystals, oriented in a magmatic flow foliation. It is characterized by two facies, one granitic and the other granodioritic. It is hosted by gneisses and has sharp and intrusive contacts, occurring as an apparently tabular body with a subhorizontal dip, but also as subvertical tabular bodies. The igneous foliation (Si) of the GPS is affected by a ductile deformation phase Dn+1, folding it, with the metamorphic foliation Sn+1 parallel to the axial plane of these folds. This phase also affects the record of a past ductile deformation Dn in host rocks. The relationship of igneous foliation with metamorphic foliation indicates that GPS emplacement occurred before the development of Sn+1 foliation. The lithogeochemical analysis indicates that the granitoid is subalkaline, metaluminous to slightly peraluminous, with shoshonitic affinity, classified as ferroan and alkali-calcic. The geochronological analyses resulted in a crystallization age (U-Pb in zircon) of 590.7±1.5 Ma. The structural, geochronological and geochemical data of the Metagranitoid Pedra Selada indicate that the magma that originated this igneous body was emplaced in extensional environment, ascending through subvertical conduits and subhorizontal spreading, forming bodies like laccoliths, in a post-collisional period to the evolution of the Southern Brasilia Belt and slightly before the collision of the Central Ribeira Belt. The magma would have an origin associated with the breaking of the subducting plate and the ascent of the asthenosphere to the base of the continental crust of the upper plate, generating partial melting and formation of slab failure to A-type plutons. The data here obtained from the GPS and from three other metagranitoid bodies and its relationships with the host rocks corroborate the interpretation of the studied region being inserted in the Nappe Socorro domain, in the Interference Zone between the Brasília and Ribeira belts.