EM - Escola de Minas
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/6
Notícias
A Escola de Minas de Ouro Preto foi fundada pelo cientista Claude Henri Gorceix e inaugurada em 12 de outubro de 1876.
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Resultados da Pesquisa
Item The Ediacaran Rio Doce magmatic arc revisited, Araçuaí-Ribeira orogenic system, SE Brazil.(2016) Tedeschi, Mahyra; Novo, Tiago Amâncio; Soares, Antônio Pedrosa; Dussin, Ivo Antonio; Tassinari, Colombo; Silva, Luiz Carlos da; Gonçalves, Leonardo Eustáquio da Silva; Alkmim, Fernando Flecha de; Lana, Cristiano de Carvalho; Dantas, Elton Luiz; Medeiros, Silvia Regina de; Campos, Cristina Maria Pinheiro de; Corrales, Felipe; Heilbron, Monica da Costa Pereira LavalleDescribed half a century ago, the Galil eia tonalite represents a milestone in the discovery of plate margin magmatic arcs in the Araçuaí-Ribeira orogenic system (southeastern Brazil). In the 1990's, analytical studies on the Galil eia tonalite finally revealed the existence of a Late Neoproterozoic calc-alkaline magmatic arc in the Araçuaí orogen. Meanwhile, the name Rio Doce magmatic arc was applied to calc-alkaline plutons found in the Araçuaí-Ribeira boundary. After those pioneer studies, the calc-alkaline plutons showing a pre-collisional volcanic arc signature and age between 630 Ma and 585 Ma have been grouped in the G1 supersuite, corresponding to the Rio Doce arc infrastructure. Here, we revisit the Rio Doce arc with our solid field knowledge of the region and a robust analytical database (277 lithochemical analyses, and 47 UePb, 53 SmeNd, 25 87Sr/86Sr and 7 LueHf datasets). The G1 supersuite consists of regionally deformed, tonalitic to granodioritic batholiths and stocks, generally rich in melanocratic to mesocratic enclaves and minor gabbroic to dioritic plutons. Gabbroic to dioritic enclaves show evidence of magma mixing processes. The lithochemical and isotopic signatures clearly reveal a volcanic arc formed on a continental margin setting. Melts from a Rhyacian basement form the bulk of the magma produced, whilst gabbroic plutons and enclaves record involvement of mantle magmas in the arc development. Tonalitic stocks (UePb age: 618e575 Ma, εNd(t): 5.7 to 7.8, Nd TDM ages: 1.28e1.68 Ga, 87Sr/86Sr(t): 0.7059e0.7118, and εHf(t): 5.2 to 11.7) form the northernmost segment of the Rio Doce arc, which dies out in the ensialic sector of the Araçuaí orogen. At arc eastern and central zones, several batholiths (e.g., Alto Capim, Baixo Guandu, Galil eia, Muniz Freire, S~ao Vítor) record a long-lasting magmatic history (632e580 Ma; εNd(t): 5.6 to 13.3; Nd TDM age: 1.35e1.80 Ga; 87Sr/86Sr(t): 0.7091 e0.7123). At arc western border, the magmatic evolution started with gabbro-dioritic and tonalitic plutons (e.g., Chaves pluton, UePb age: 599 ± 15 Ma, εNd(t): 4.8 to 6.8, Nd TDM ages: 1.48e1.68 Ga, 87Sr/86Sr(t): 0.7062e0.7068, and εHf(t): 4.3 to 9.7; and Brasil^andia pluton, UePb age: 581 ± 11 Ma, εNd(t): 8.2 to 10.2, Nd TDM ages: 1.63e1.68 Ga, 87Sr/86Sr(t): 0.7088e0.7112, εHf(t): 12.3 to 14.9),followed by late granodioritic intrusions (e.g., Guarataia pluton, UePb age: 576 ± 9 Ma, εNd(t): 12.52 to 13.11, Nd TDM age: 1.74e2.06 Ga, 87Sr/86Sr(t): 0.7104e0.7110, εHf(t): 12.9 to 21.6). The Muria e batholith (UePb age: 620e592 Ma, εNd(t): 8.2 to 13.6, Nd TDM age: 1.41e1.88 Ga) and the Conceiç~ao da Boa Vista (586 ± 7 Ma) and Serra do Valentim (605 ± 8 Ma) stocks represent a segment of the Rio Doce arc correlated to the Serra da Bolívia and Marceleza complexes, making the link between the Araçuaí and Ribeira orogenic domains. We suggest three phases of arc development: i) eastward migration of arc front (632e605 Ma), ii) widespread magma production in the whole arc (605e585 Ma), and iii) late plutonism in the western arc region (585e575 Ma). Usual processes of volcanic arc development, like subduction of oceanic lithosphere under a continental margin, followed by asthenosphere ascent related to slab retreating and break-off may explain the Rio Doce arc evolution.Item New U-Pb ages and lithochemical attributes of the Ediacaran Rio Doce magmatic arc, Araçuaí confined orogen, southeastern Brazil.(2014) Gonçalves, Leonardo Eustáquio da Silva; Farina, Federico; Lana, Cristiano de Carvalho; Soares, Antônio Carlos Pedrosa; Alkmim, Fernando Flecha de; Nalini Júnior, Hermínio AriasThe Araçuaí orogen of southeastern Brazil, together with its counterpart located in Africa, the West Congo belt, formed through closure of a gulf connected to the Adamastor Ocean by the end of the Ediacaran and beginning of the Cambrian. Convergence of the margins of the gulf led to the development of the Rio Doce magmatic arc between 630 Ma and 580 Ma on a continental basement mostly composed of Rhyacian orthogneisses. The Rio Doce arc mainly consists of tonalite-granodiorite batholiths, generally crowded with mafic to dioritic enclaves, and minor gabbronorite-enderbite-charnockite plutons, suggesting mixing processes involving crustal and mantle sources. We investigate the basement, magma sources and emplacement ages of the Rio Doce arc. Our data suggest the arc comprises three main granitic rock groups: i) Opx-bearing rocks mostly of enderbite to charnockite composition; ii) enclaverich tonalite-granodiorite (ETG); and iii) enclave-poor granite-granodiorite with minor tonalite (GT). The Opx-bearing rocks are magnesian, calc-alkalic to alkali-calcic and metaluminous. Together, the ETG and GT rock groups range in composition from tonalite to granite, are metaluminous to slightly peraluminous, show a predominantly medium- to high-K, expanded calc-alkaline signature, and other geochemical and isotopic attributes typical of a pre-collisional volcanic arc formed on a continental margin setting. Mineralogical, chemical, and geochronological data suggest the involvement of HTmelting of granulitic (H2O-depleted) sources of Rhyacian age for the generation of Opx-bearing granitic rocks, additionally to magma mixing and fractional crystallization processes. In conclusion, the studied rock groups of the Rio Doce arc were likely formed by interactions of mantle and crustal processes, in an active continental margin setting. These processes involved ascent of mantle magmas that induced partial melting on the continental basement represented by the Rhyacian gneisses.