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This paper focuses on pressure- and temperature path analyses in paragneisses from a metasedimentary succession (MSS) in the south western Aracuai orogen. The sampling area is limited by the Abre Campo shear zone (West) and the Rio Doce Magmatic Arc (East). This region is rich in ortho-derived metamorphic basement rocks (Mantiqueira and the Juiz de Fora complexes) and para-derived metamorphic rocks, including paragneisses interlaid by quartzites, which form the MSS. The sampled rocks are mainly compost of quartz, plagioclase, garnet, K-Feldspar, orthopyroxene and sillimanite. Measurement spot profiles through garnet porphyroblasts show a certain zonation characterised by decrease in pyrope and the increase in almandine from the core to the rim. This implies retrograde growth. Metamorphic conditions are of high amphibolite- to granulite facies with maximum pressure of ca. 6 kbar and maximum temperature of ca. 700°C. The data suggest that the cores of the garnet porphyroblasts of MSS started to grow during the final deformation stage of the Aracuai orogen (south western part); the event of decompression is captured in the rims of the porphyroblasts and related to the gravitational collapse in the Cambrian. Keywords: P-T path, metasedimentary succession, geothermobarometry, Aracuai orogen Resumo: RECONSTRUCAO DE TRAJETORIAS P-T EM PARAGNAISSES GRANADIFEROS NEOPROTEROZOICOS DA UMA SUCESSAO METASSEDIMENTAR NO SUDOESTE DO OROGENO ARACUAI, MINAS GERAIS, BRASIL. Este estudo foca analises de caminhos de pressao e temperatura em paragnaisses de sucessao metassedimentar (SMS) da regiao sudoeste do Orogeno Aracuai. A area de amostragem e limitada pela zona de cisalhamento de Abre Campo a oeste e pelo Arco Magmatico Rio Doce a leste. A regiao e rica em rochas metamorficas de alto grau ortoderivadas (complexos Mantiqueira e Juiz de Fora do embasamento) e paraderivadas; incluindo paragnaisses intercalados a quartzitos, que formam o SMS. As rochas amostradas sao compostas por quartzo, plagioclasio, granada, feldspato potassio, ortopiroxenio e sillimanita. Perfis de pontos de analise em porfiroblastos de granada mostram certo zoneamento caracterizado pela reducao de piropo e por aumento de almadina do nucleo para borda; isto implica em crescimento de cristal sob condicoes de metamorfismo retrogrado. Condicoes metamorficas sao de facies anfibolito alto a granulito com um maximo de pressao de ca. 6 kbar e com temperatura maxima de ca. 700°C. Os dados sugerem que porfiroblastos de granada da SMS tem nucleacao e inicio de crescimento durante o final da etapa deformacional principal compressiva do Orogeno Aracuai (regiao sudoeste do orogeno); o evento de descompressao captado em bordas dos porfiroblastos foi relacionando ao colapso gravitacional no Cambriano. Palavras-chave: Trajetorias P-T, sucessao metassedimentar, geotermobarometria, Orogeno Aracuai

geonomos

P- T PATH RECONSTRUCTION IN NEOPROTEROZOIC GARNET-BEARING PARAGNEISSES FROM A METASEDIMENTARY SUCCESSION OF THE SOUTH WESTERN ARAÇUAÍ OROGEN, MINAS GERAIS, BRAZIL