AS ROCHAS METABÁSICAS DO SUPERGRUPO AÇUNGUI, FOLHA TOPOGRÁFICA ARAÇAÍBA, SUDESTE DO ESTADO DE SÃO PAULO: The metabasic rocks from Açungui Supergroup, Araçaíba topographic map, Southeast of São Paulo State

Abstract

The ortho-derived rocks of basic and ultrabasic composition of meso- to neoproterozoic age of the region of Araçaiba, southwest of the state of São Paulo, are constituted by amphibolites and metabasites are located in the portion northern of the Apiaí Terrain, associated with the rocks of the metavolcanic sedimentary sequences of the Açungui Supergroup, specifically in the rocks of the Água Clara Formation. The main mineral paragenesis consists igneous pseudomorph of piroxene ± labradorite, ferrohornblende- magnesiohornblende ± oligoclase / andesine, representing the progressive regional metamorphism M1 climax, from 579 °C to 606 °C in temperature and 6.6 kbar (± 0, 6), mid amphibolite facies; and of magnesiohornblenda- actinolita ± albite, from M3 regional retrometamorphism, low to mid greenschist facies. Geochemical data classify the igneous protoliths as into sub-alkaline low-potassium Fe-tholeitic gabbro and monzogabbro and alkaline picrite with a tendency to komatiitic basalts. Geotectonic data, corroborated by the behavior of trace elements and REEs, indicate three main signatures for amphibolitic groups: basic tholeitic and komatiitic rocks associated with mid-ocean ridge (MORB), with possible crust interaction in subduction phase; ultrabasic alkaline ocean island rocks (OIA); and island arc tholeiitic basalts (IAT). Therefore, this magmatism is correlated to the initial stage of opening of the basin or to the beginning of closure, to the initial phase of tholeitic ocean floor nature, associated with ocean island alkaline basalts. Keywords: geology, geochemistry, metabasic, Açungui SupergroupRESUMO – As rochas ortoderivadas de composição básica e ultrabásica de idade meso- a neoproterozoica da região de Araçaíba, sudeste do estado de São Paulo, são constituídas por anfibolitos e metabasitos situados na porção norte do Terreno Apiaí, associados as rochas das sequências metavulcanossedimentares do Supergrupo Açungui, especificamente as rochas da Formação Água Clara. A paragênese mineral é constituída de pseudomorfos ígneos piroxênios ± labradorita, magnesiohornblenda ± oligoclásio/andesina, representando o ápice do metamorfismo regional progressivo M1, de 579°C a 606°C de temperatura e 6,6 kbar (±0,6) em fácies anfibolito médio; e magnesiohornblenda-actinolita ± albita, do retrometamorfismo regional M3 em fácies xisto verde baixo a médio. Dados geoquímicos classificam os protólitos ígneos máficos em gabro e monzogabro Fe-toleíticos sub alcalinos de baixo potássio e picrito alcalinos com tendência a basaltos komatiíticos. Os dados geotectônicos indicam três assinaturas principais para os grupos anfibolíticos: rochas básicas toleíticas a komatiíticas associadas à cadeia mesoceânicas (MORB), a partir da interação fonte mantélica do tipo E-MORB enriquecida ou pela interação supracrustais durante a subducção; rochas ultrabásicas alcalinas de ilha oceânica (OIA); e basaltos toleíticos de arco de ilha (IAT). Portanto, os eventos magmáticos estão correlacionados ao estágio inicial de abertura de bacia ou ao início de fechamento à fase inicial de natureza toleítica de fundo oceânico, associado a basaltos alcalinos de ilha oceânica. Palavras-chave: Geologia. Geoquímica. Metabásica, Supergrupo Açungui.   ABSTRACT – The ortho-derived rocks of basic and ultrabasic composition of meso- to neoproterozoic age of the region of Araçaiba, southeast of the state of São Paulo, are constituted by amphibolites and metabasites are located in the portion northern of the Apiaí Terrain, associated with the rocks of the metavolcanic sedimentary sequences of the Açungui Supergroup, specifically in the rocks of the Água Clara Formation. The main mineral paragenesis consists igneous pseudomorph of piroxene ± labradorite, ferrohornblende- magnesiohornblende ± oligoclase / andesine, representing the progressive regional metamorphism M1 climax, from 579 °C to 606 °C in temperature and 6.6 kbar (± 0, 6), mid amphibolite facies; and of magnesiohornblende-actinolite ± albite, from M3 regional retrometamorphism, low to mid greenschist facies. Geochemical data classify the igneous protoliths as into sub-alkaline low-potassium Fe-tholeitic gabbro and monzogabbro and alkaline picrite with a tendency to komatiitic basalts. Geotectonic data, corroborated by the behavior of trace elements and REEs, indicate three main signatures for amphibolitic groups: basic tholeitic and komatiitic rocks associated with mid-ocean ridge (MORB), with possible crust interaction in subduction phase; ultrabasic alkaline ocean island rocks (OIA); and island arc tholeiitic basalts (IAT). Therefore, this magmatism is correlated to the initial stage of opening of the basin or to the beginning of closure, to the initial phase of tholeitic ocean floor nature, associated with ocean island alkaline basalts. Keywords: Geology. Geochemistry. Metabasic. Açungui Supergroup