Geotermobarometria das rochas do Grupo Araxá e do Complexo Guaxupé na região de Guaxupé - Nova Resende, MG
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Data
2019-01-09
Autores
Leme, Thaís Güitzlaf [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
A área de estudo situa-se no sul da Faixa Brasília Meridional, no sudoeste do estado de Minas Gerais e compreende uma faixa entre os municípios de Guaxupé, Monte Belo, Nova Resende e São Pedro da União, no contato entre as unidades que compõem o Complexo Guaxupé e litotipos atribuídos ao Grupo Araxá. Esta região situa-se em uma zona de blocos crustais amalgamados durante a orogênese brasiliana no Neoproterozoico e marca o limite entre terrenos granulíticos (Complexo Guaxupé) e litotipos adjacentes envolvidos no processo colisional e pós colisional (Grupo Araxá). Este contato é delimitado pela Zona de Cisalhamento Varginha, que representa uma quebra nas condições metamórficas entre as unidades. Neste trabalho são apresentados dados petrográficos, de química mineral e geotermobarométricos (média P-T calculada pelo software THERMOCALC, software RCLC e geotermômetros Zr-em-rutilo e Ti-em-quartzo) com o objetivo de investigar e determinar as condições de pressão e temperatura dos litotipos que ocorrem no contato entre o Complexo Guaxupé e o Grupo Araxá nessa região. Na área de estudo, o Complexo Guaxupé é constituído principalmente por rochas ortoderivadas de natureza básica a ácida, com predomínio de composições intermediárias, representadas por granulitos (ortopiroxênio gnaisses) félsicos a máficos, com intercalações de anfibólio e/ou biotita gnaisses (sem ortopiroxênio), além de intercalações de metassedimentos com sillimanita, granada, ortoclásio e rutilo. O Grupo Araxá é constituído por metassedimentos pelíticos a psamo-pelíticos com intercalações de ortognaisses e de rochas metamáficas e metaultramáficas, representados por gnaisses paraderivados e ortoderivados de composição granítica a tonalítica, quartzitos e xistos com granada e cianita, além de rochas metamáficas com granada, clinopiroxênio e anfibólio. As feições mineralógicas e texturais, associadas aos dados de química mineral e de geotermobarometria, indicam, para o Complexo Guaxupé, condições de auge metamórfico balizado em torno de 1.000-1.050ºC e pressão da ordem de 14,0 kbar em fácies granulito, no campo de estabilidade da sillimanita, próximo ao limite entre os campos de estabilidade da cianita-sillimanita e condições de reequilíbrio de 950 a 700ºC e 13,5 a 11,0 kbar. No Grupo Araxá, o auge metamórfico atingiu condições de fácies eclogito, com temperaturas da ordem de 900ºC e pressões superiores a 15,0 kbar e condições de reequilíbrio de 850 a 700ºC e 13,5 a 11,0 kbar, em fácies granulito a anfibolito superior, no campo de estabilidade da cianita. Os dados apresentados são compatíveis com regime P-T-t típico de zonas de espessamento crustal (colisão continental).
The study area is located at the south of Southwerst Brasília Belt, southeast of Minas Gerais, and it comprehends a strip among the cities of Guaxupé, Monte Belo, Nova Resende and São Pedro da União, in contact with unities that compose the Guaxupé Complex and lithotypes attributed to the Araxá Group. This region is in a zone with crustal blocks amalgamated during the Brazilian orogenesis in Neoproterozoic, and it determines the limit between granulitic terrains (Guaxupé Complex) and adjacent lithotypes involved in collisional and post-collisional processes (Araxá Group). The contact is delimitated by the Varginha Shear Zone, which represents a disruption of metamorphic conditions amid the unities. This paper presents petrographic, mineral chemistry and geothermobarometric data (average P-T calculated by the THERMOCALC software, software RCLC and geothermometers Zr-in-rutile and Ti-in-quartz) in order to investigate and determine the pressure and temperature conditions of the lithotypes that occur in the contact between the Guaxupé Complex and Araxá Group. In the study area, the Guaxupé Complex consists especially ortho-derivative rocks of basic to acidic nature, represented by felsic to mafic granulites (orthopyroxene gneisses), and amphibole and/or biotite gneisses intercalations (orthopyroxene free), as well as metasediments intercalations with sillimanite, garnet, orthoclase and rutile. The Araxá Group consists of pelitic to psamo-pelites metasediments with orthogneisses, metamafic and metaultramafic rocks intercalations, represented by para and ortho-derivative gneisses of granitic to tonalitic composition, quartzites and schists with garnet and kyanite, and metamafic rocks with garnet, clinopyroxene and amphibole. Mineralogical and textural aspects, associated to mineral chemistry and geothermobarometric data, indicate, for the Guaxupé Complex, conditions of metamorphic peak at 1.000-1.050ºC, and pressure in order of 14,0 kbar in granulite facies, within the sillimanite stability field near to the boundary between the sillimanite-kyanite stability field and rebalancing conditions of 950 to 700 °C and 13,5 to 11,0 kbar. In the Araxá Group, metamorphic peak reached eclogite facies conditions, with temperatures in order of 900ºC, pressures higher than 15,0 kbar, and rebalancing conditions of 850 to 700ºC and 13,5 to 11,0 kbar, in granulite to upper amphibolite facies in the kyanite stability field. The data presented in this work are compatible with the typical P-T-t regime of crustal thickening zones (continental collision).
The study area is located at the south of Southwerst Brasília Belt, southeast of Minas Gerais, and it comprehends a strip among the cities of Guaxupé, Monte Belo, Nova Resende and São Pedro da União, in contact with unities that compose the Guaxupé Complex and lithotypes attributed to the Araxá Group. This region is in a zone with crustal blocks amalgamated during the Brazilian orogenesis in Neoproterozoic, and it determines the limit between granulitic terrains (Guaxupé Complex) and adjacent lithotypes involved in collisional and post-collisional processes (Araxá Group). The contact is delimitated by the Varginha Shear Zone, which represents a disruption of metamorphic conditions amid the unities. This paper presents petrographic, mineral chemistry and geothermobarometric data (average P-T calculated by the THERMOCALC software, software RCLC and geothermometers Zr-in-rutile and Ti-in-quartz) in order to investigate and determine the pressure and temperature conditions of the lithotypes that occur in the contact between the Guaxupé Complex and Araxá Group. In the study area, the Guaxupé Complex consists especially ortho-derivative rocks of basic to acidic nature, represented by felsic to mafic granulites (orthopyroxene gneisses), and amphibole and/or biotite gneisses intercalations (orthopyroxene free), as well as metasediments intercalations with sillimanite, garnet, orthoclase and rutile. The Araxá Group consists of pelitic to psamo-pelites metasediments with orthogneisses, metamafic and metaultramafic rocks intercalations, represented by para and ortho-derivative gneisses of granitic to tonalitic composition, quartzites and schists with garnet and kyanite, and metamafic rocks with garnet, clinopyroxene and amphibole. Mineralogical and textural aspects, associated to mineral chemistry and geothermobarometric data, indicate, for the Guaxupé Complex, conditions of metamorphic peak at 1.000-1.050ºC, and pressure in order of 14,0 kbar in granulite facies, within the sillimanite stability field near to the boundary between the sillimanite-kyanite stability field and rebalancing conditions of 950 to 700 °C and 13,5 to 11,0 kbar. In the Araxá Group, metamorphic peak reached eclogite facies conditions, with temperatures in order of 900ºC, pressures higher than 15,0 kbar, and rebalancing conditions of 850 to 700ºC and 13,5 to 11,0 kbar, in granulite to upper amphibolite facies in the kyanite stability field. The data presented in this work are compatible with the typical P-T-t regime of crustal thickening zones (continental collision).
Descrição
Palavras-chave
Petrografia, Granulitos, Zona de Cisalhamento Varginha, Faixa Brasília Meridional, Petrography, Granulites, Varginha Shear Zone, Southern Brasília Belt