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• W2079732760 abstract "The Araçuaí Belt is a Late Proterozoic (Brasiliano Cycle) geotectonic unit which was developed along the southeastern margin of the São Francisco Craton (SE Brazil) and was formerly considered as being an ensialic orogen. It is correlated with the Pan-African West Congolian Belt (SW Africa) in many reports. In the western domain of the belt, the Macaúbas Group—the most important supracrustal sequence related to the evolution of the Araçuaí Belt —comprises the Terra Branca and Carbonita Formations, which consist of littoral glacial sediments to shelf turbidites. These formations grade upward and eastward to the Salinas Formation, consisting of distal turbidites related to submarine fans, pelagic sediments, and a rock association (the Ribeirão da Folha Facies) typical of an ocean-floor environment. Banded iron formations, metacherts, diopsidites, massive sulfides, graphite schists, hyperaluminous schists, and ortho-amphibolites, intercalated with quartz-mica schists and impure quartzites, characterize the most distinctive and restricted volcano-sedimentary facies yet found within the Salinas Formation. Ultramafic slabs were tectonically emplaced within the Ribeirão da Folha Facies. Eight whole rock samples of meta-ultramafic rocks and ortho-amphibolites yielded a SmNd isochronic age of 793 ± 90 Ma (ϵNd(T) = +4.1 ± 0.6. MSWD = 1.76 ). The structures of the northern Araçuaí Belt are marked by a doen-dip stretching lineation (western domain) related to frontal thrusts which controlled tectonic transport from east to west; stretching lineation rakes decrease in the eastern tectonic domain, indicating dominant oblique to transcurrent motion; the northern arch of the belt is characterized by major high-dip transcurrent shear zones. Our tectonic model starts with marked fracturing, followed by rifting that took place in the São Francisco-Congo Craton around 1000 ± 100 Ma (ages of basic intrusions and alkaline anorogenic granites). A sinistral transfer zone was established at the north rn boundary of the belt, controlling the ellargement of the Araçuaí-West Congolian rift, with the neighbouring northern cratonic region remaining essentially unaffected by compressional stresses. A period of ocean-floor spreading took place at about 800 Ma. Rift closure started at about 750 Ma and led to the reversal of motion along former extensional structures. The main Brasiliano-Pan-African orogenic period took place between 700 and 550 Ma and was marked by regional metamorphism and deformation related to both thrusting and transcurrent movements, and emplacement of syntectonic grranites derived from anatectic melts trigered by collisional crustal thickening. In this period, ultramafic slabs were emmlaced within the Ribeirão da Folha Facies, and both may represent an ophiolite-type suite. Late- to post-tectonic (500 to 550 Ma) intrusive granites were generated and emplaced in the Brazilian side along a major zone of crustal thickening in response to the last stages of collision. Este trabalho apresenta novos dados estratigráficos, estruturais e geocronológicos (método SmNd), além de concisa revisão bibliográfica, que embasam a proposição de um novo modelo tectônico para Faixa Araçuaí-Oeste Congolesa (Ciclo Brasiliano-Panafricano). O Grupo Macaúbas, unidade-chave da Faixa Araçuaí, é dividido nas formações Terra Branca, Carbonita e Salinas. As duas primeiras englobam desde sedimentos glacio-costeiros, a oeste, até turbiditos plataformais e gradam, vertical e lateralmente (no sentido leste), para a Formação Salinas, que compreende turbiditos distais relacionados a leques submarinos, sedimentos pelágicos e um conjunto de rochas típico de assoalho oceânico. Este conjunto é representado pela Fácies Ribeirão da Folha, constituida por formações ferríferas bandadas, metacherts, diopsiditos, sulfetos maciços, grafita xistos, xistos hiper-aluminosos e orto-anfibolitos, intercalados em quartzo-mica xistos e quartzitos. Corpos de rochas meta-ultramáficas encontram-se tectonicamente encaixados nesta pilha vulcano-sedimentar. A idade isocrônica Sm-Nd (RT, 8 pontos) dos orto-anfibolitos e rochas meta-ultramáficas é 793 ± 90 Ma (ϵNd(T) = +4,1 ± 0,6; MSWD = 1,76). Os padrões tectônicos da Faixa Araçuaí mostram que o domínio ocidental é caracterizado por lineação de estiramento down-dip, relacionada aos empurrões que controlaram o transporte tectônico no sentido oeste; a obliquidade (rake) da lineação de estiramento decresce no domínio oriental, indicando movimentos oblíquos a transcorrentes e o arco norte da faixa é caracterizado por zonas de cisalhamento transcorrentes. A abordagem do modelo evolutivo proposto começa em 1000 ± 100 Ma (idades de intrusões básicas e granitos alcalinos anorogênicos), quando o Craton do São Francisco-Congo foi afetado por marcante fraturamento. O rift Araçuaí-Oeste Congolês começou a ser aberto no início deste período e uma zona de transferência do movimento estruturou-se em sua borda norte, controlando o alargamento do rift. A zona de transferência sinistral, tendo tomado o controle maior do deslocamento, acomodou a deformação resultante do alargamento do rift e inibiu os efeitos compressivos sobre a região aratônica ao norte da faixa. Espalhamento de fundo oceânico teve início em torno de 800 Ma originando segmentos de crosta oceânica. O fechamento do rift começou em torno de 750 Ma e ocasionou a reversõo do movimento nas estruturas extensionais. Entre 700 e 550 Ma ocorreu o período orogenético principal, acarretando metamorfismo regional relacionado á deformação dada pelos movimentos de empurrão e transcorrência e alojamento de granitos sin-tectônicos derivados de fusões anatéticas geradas numa crosta em espessamento. Lascas tectônicas de rochas ultramáficas foram alojadas na Fácies Ribeirão da Folha, sugerindo uma suite tipo-ofiolito. Finalmente, granitos intrusivos tardi- a pós-tectônicos (550 a 500 Ma) formaram-se e ascenderam, na Faixa Araçuaí, ao longo da zona de pronunciado espessamento crustal resultante dos últimos estágios colisionais." @default.
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• W2079732760 title "Toward a new tectonic model for the Late Proterozoic Araçuaí (SE Brazil)-West Congolian (SW Africa) Belt" @default.
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