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Autor(es)

Melina Cristina Borges Esteves

• Tipo de documento: Dissertação de Mestrado
• Imprenta: São Paulo.
• Instituição: Universidade de São Paulo (USP). Instituto de Geociências
• Data de defesa: 11 maio 2018

Membros da banca

Frederico Meira Faleiros; Rodrigo Prudente de Melo; Lena Virginia Soares Monteiro

• Orientador: Frederico Meira Faleiros

Resumo

P-T conditions existing at the tectonic event that acted at the fold-and-thrust zone of the western margin of the São Francisco Craton were estimated on the basis of structural, microstructural, petrographic and fluid inclusion study of syntectonic veins. The presence of veins of different generations in the fold-and-thrust zone is evidenced by fluids operating at different scenarios of paleostress throughout the deformation history. The area are composed of weakly deformed rocks of the Bambuí Group recording a metamorphism with conditions ranging from diagenetic to sub-greenschist facies. Two tectonic events were identified by vein geometric arrangement and folded surface, a major early NE-SW compression (D1 - \'sigma\'1 subhorizontal SW-trending and \'sigma\'3 subvertical), related with subhorizontal NW-trending syntectonic veins formed at conditions that have reached at least 140°C and pressures around 200-363 MPa; and later NW-SE compression (D2 - \'sigma\'1 subhorizontal NW-trending and \'sigma\'3 subhorizontal NE-trending), related with subvertical syntectonic cleavage-parallel veins formed at the same range of temperature and pressures between 181-295 MPa. Indication of fluctuations in pressure during these events played a crucial role as fluids significantly influence the mechanical processes, deformation mechanisms and chemical reactions that operate in fold-thrust belts. Fluids show H2O-NaCl-CaCl2 composition where mixing process of different fluids sources (metamorphic and meteoric) are evidenced by evolutive trending of homogenization temperatures and salinities resulting in some variation in salinity (12 against 4 wt.% NaCl eq. for subhorizontal and cleavage-parallel veins respectively). This research confirms that combine the reconstruction of the paleostress states and fluid inclusion studies can provide fundamental information of relationship between fluid flow and tectonic of orogenic terrains contributing to the scientific knowledge about the deformational/metamorphic evolution of the Bambuí Group and the fold-and-thrust zone of the western margin of the São Francisco Craton. (AU)

• Processo FAPESP: 15/13901-1 - História térmica e circulação de fluidos em estruturas deformacionais associadas ao Grupo Bambuí na porção externa da Faixa Brasília (Unaí, mg)
• Beneficiário: Melina Cristina Borges Esteves
• Linha de fomento: Bolsas no Brasil - Mestrado