Condições de metamorfismo na porção centro-norte da Nappe Socorro-Guaxupé: aplicação da geotermometria de elementos traço em paragnaisse da região de São José do Rio Pardo-Caconde (SP)
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2022-03-14
Autores
Dias, João Guilherme Pereira
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Universidade Estadual Paulista (Unesp)
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A Nappe Socorro-Guaxupé (NSG) é um terreno cristalino alóctone neoproterozoico metamorfisado sob condições de fácies granulito. A NSG foi formada em um ambiente de arco magmático, que foi estabelecido na borda oriental do paleocráton Parapanema, durante o Neoproterozoico. Esse terreno foi dividido em três unidades: a basal granulítica, cujo principal litotipo é o granulito enderbítico, intercalado por gnaisses gabro-noríticos; a intermediária diatexítica composta por migmatitos metaluminosos, com granitos e ortognaisses anatéticos; e a superior metatexítica constituída por migmatitos pelíticos a semipelíticos. Rochas metamórficas de alto grau (fácies anfibolito a granulito) compõe os principais litotipos da região de São José do Rio Pardo e Caconde (SP) tais como migmatitos variados, gnaisses paraderivados (pelíticos e cálcio-silicáticos), rochas charnockíticas e metamáficas, como anfibolito e granulito máfico. Esse trabalho tem como objetivo principal determinar as condições P-T do metamorfismo de fácies granulito em paragnaisse pelítico da região de São José do Rio Pardo e Caconde (SP) (região centro-norte da Nappe Socorro-Guaxupé). Para tal, foram realizadas descrições macroscópicas e petrográficas, bem como análises químicas quantitativas em Microssonda Eletrônica, a fim de empregar de forma integrada os geotermômetros Zr-no-rutilo e Ti-no-quartzo. Os resultados obtidos para ambos os geotermômetros foram processados e interpretados de forma integrada. As condições metamórficas obtidas estão em torno de 8,5 a 13,5 kbar e 790 a 870°C e são consideradas retrometamórficas devido a várias texturas específicas identificadas durante a descrição petrográfica. Conclui-se que essa condições P-T representam um retrometamorfismo que ocorreu na área durante o resfriamento do sistema após o auge metamórfico. Supõe-se que, se as condições retrometamórficas registradas pelo litotipo aqui estudado apresentam temperaturas tão elevadas, então é possível que o conjunto litológico das regiões de São José do Rio Pardo e Caconde tenham atingido condições de ultra-alta temperatura durante o ápice metamórfico, tal como já reconhecido em alguns litotipos do Nappe Socorro-Guaxupé.
The Socorro-Guaxupé Nappe (SGN) is a Neoproterozoic crystalline terrain, metamorphosed under granulite facies. The SGN was formed in a magmatic arc environment, which was established during the Neoproterozoic, in the eastern section of the Paranapanema paleocraton. This terrain was divided in three units: The basal granulitic, in which the main lithotype is the enderbitic granulite, intercalated with gabro-noritic gneiss; the diatexitic composed by meta-luminous migmatites, with anatetics granites and orthogneiss; and the upper metatexitic constituted by pelitic and semi-pelitic migmatites. High grade metamorphic rocks (upper amphibolite to granulite facies) composes the main lithotypes of the São José do Rio Pardo and Caconde (SP) region such as migmatites, pelitic and calc-silicate gneiss, charnockitic rocks and metamafics, such as, amphibolites and mafic granulites. The main objective of this work is to determine both the P-T conditions from the metamorphism of granulite facies in pelitic paragnaisses from the São José do Rio Pardo and Caconde (SP) (central-northern region from the Socorro-Guaxupé Nappe). For such, macroscopic and petrographic descriptions, as well as quantitative chemical analyses with electron probe microanalyzer were conducted in order to use the Zr-in-rutile and Ti-in-quartz geothermometers. The results from both geothermometers were processed and interpretated in an integrated way. The metamorphic conditions obtained are around 8.5 to 13.5 kbar and 790°C to 870°C and are considered retrometamorphic due to several specific textures identified during petrographic description. Therefore, it is concluded that these P-T conditions represent a retrometamorphism that occurred in the area during the cooling of the system after the metamorphic peak. It is supposed that, if the retrometamorphic conditions registered by the hereby studied lithotype presents such elevated temperatures, so it is possible that the lithological grouping of the São José do Rio Pardo and Caconde may have reached ultra-High temperatures during the metamorphic peak, as already acknowledge in some lithotypes of the Socorro-Guaxupé Nappe.
The Socorro-Guaxupé Nappe (SGN) is a Neoproterozoic crystalline terrain, metamorphosed under granulite facies. The SGN was formed in a magmatic arc environment, which was established during the Neoproterozoic, in the eastern section of the Paranapanema paleocraton. This terrain was divided in three units: The basal granulitic, in which the main lithotype is the enderbitic granulite, intercalated with gabro-noritic gneiss; the diatexitic composed by meta-luminous migmatites, with anatetics granites and orthogneiss; and the upper metatexitic constituted by pelitic and semi-pelitic migmatites. High grade metamorphic rocks (upper amphibolite to granulite facies) composes the main lithotypes of the São José do Rio Pardo and Caconde (SP) region such as migmatites, pelitic and calc-silicate gneiss, charnockitic rocks and metamafics, such as, amphibolites and mafic granulites. The main objective of this work is to determine both the P-T conditions from the metamorphism of granulite facies in pelitic paragnaisses from the São José do Rio Pardo and Caconde (SP) (central-northern region from the Socorro-Guaxupé Nappe). For such, macroscopic and petrographic descriptions, as well as quantitative chemical analyses with electron probe microanalyzer were conducted in order to use the Zr-in-rutile and Ti-in-quartz geothermometers. The results from both geothermometers were processed and interpretated in an integrated way. The metamorphic conditions obtained are around 8.5 to 13.5 kbar and 790°C to 870°C and are considered retrometamorphic due to several specific textures identified during petrographic description. Therefore, it is concluded that these P-T conditions represent a retrometamorphism that occurred in the area during the cooling of the system after the metamorphic peak. It is supposed that, if the retrometamorphic conditions registered by the hereby studied lithotype presents such elevated temperatures, so it is possible that the lithological grouping of the São José do Rio Pardo and Caconde may have reached ultra-High temperatures during the metamorphic peak, as already acknowledge in some lithotypes of the Socorro-Guaxupé Nappe.
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Geologia, Geotermômetros, Retrometamorfismo, Nappe Socorro-Guaxupé, Elementos-traço, Paragnaisse, Pressão, Temperatura, Geothermomether, Trace-elements, Pressure, Temperature, Retrometamorphism