Petrografia e geoquímica da ocorrência de (clinopiroxênio)-hastingsita-biotita-granada ortognaisse na região de Santa Cruz do Prata - MG

• Autor(a) principal: Leme, Thaís Guitzlaf [UNESP]
• Data de Publicação: 2016
• Tipo de documento: Trabalho de conclusão de curso
• Idioma: por
• Título da fonte: Repositório Institucional da UNESP
• Texto Completo: http://hdl.handle.net/11449/155487; http://www.athena.biblioteca.unesp.br/exlibris/bd/capelo/2017-06-06/000884847.pdf
• topic: Petrologia; Geoquimica; Cisalhamento dos solos; Minas Gerais

In the region of Santa Cruz do Prata, southwest of Minas Gerais, the occurrence of (clinopyroxene)-hastingsite-biotite-garnet orthogneiss was recorded between rocks attributed to the Araxá Group, close to the tectonic contact with lithotypes attributed to the Guaxupé Complex. The mineral assemblage present in the orthogneiss is uncommon, and not completely described and understood in the region. In this work are presented petrographic, geochemical, of mineral chemistry, thermobarometric and isotopic data with the purpose of characterizing the occurrence of this lithotype. This rock has structures that varies from isotropic to anisotropic, and may show much more foliated and oriented domains, due to the greater degree of deformation. In the less deformed portions it is possible to identify preserved primary igneous features. The mineralogical, textural, and petrological aspects suggest that the orthogneiss protolith was a granitic rock composed of orthoclase, plagioclase, garnet, clinopyroxene and quartz, originated under conditions of minimum temperatures of 900 °C, and pressures above 15 Kbar. The lithogeochemical analyzes show that the orthogneiss presents a calcic-alkaline chemical composition, with metaluminous to peraluminous character, classified as granodiorite to granite, with compositional characteristics similar to that of rocks generated in magmatic arcs. The obtained data indicate metamorphic peak under granulite facies conditions, with minimum temperatures of 800 °C and pressures higher than 12.5 kbar, and retrometamorphic re-equilibrium under conditions of 670 °C to 750 °C and 10.0 kbar to 12.5 Kbar in medium to high amphibolite facies, with metamorphic trajectory clockwise, compatible with continental collision zones