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Tedeschi, Mahyra; Novo, Tiago; Pedrosa-Soares, Antônio; Dussin, Ivo; Tassinari, Colombo; Silva, Luiz Carlos; Goncalves, Leonardo; Alkmim, Fernando; Lana, Cristiano; Figueiredo, Célia; Dantas, Elton; Medeiros, Sílvia; De Campos, Cristina; Corrales, Felipe; Heilbron, Mônica (2016): The Ediacaran Rio Doce magmatic arc revisited (Aracuai-Ribeira orogenic system, SE Brazil). In: Journal of South American Earth Sciences, Vol. 68: pp. 167-186
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Abstract

Described half a century ago, the Galileia tonalite represents a milestone in the discovery of plate margin magmatic arcs in the Aracual-Ribeira orogenic system (southeastern Brazil). In the 1990's, analytical studies on the Galileia tonalite finally revealed the existence of a Late Neoproterozoic calc-alkaline magmatic arc in the Aracuai orogen. Meanwhile, the name Rio Dace magmatic arc was applied to talc-alkaline plutons found in the Aracual-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 U-Pb, 53 Sm-Nd, 25 Sr-87/Sr-86 and 7 Lu-Hf 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 (U-Pb age: 618-575 Ma, epsilon Nd-(t): -5.7 to -7.8, Nd T-DM ages: 1.28-1.68 Ga, Sr-87/Sr-86(t): 0.7059-0.7118, and epsilon Hf-(t): -5.2 to -11.7) form the northernmost segment of the Rio Doce arc, which dies out in the ensialic sector of the Aracuai orogen. At arc eastern and central zones, several batholiths (e.g., Alto Capim, Baixo Guandu, Galileia, Muniz Freire, Sao Vftor) record a long-lasting magmatic history (632-580 Ma;epsilon Nd-(t): -5.6 to -13.3;Nd T-DM age: 135-1.80 Ga;Sr-87/Sr-86(t): 0.7091 -0.7123). At arc western border, the magmatic evolution started with gabbro-dioritic and tonalitic plutons (e.g., Chaves pluton, U-Pb age: 599 +/- 15 Ma, epsilon Nd-(t): -4.8 to -6.8, Nd T-DM ages: 1.48-1.68 Ga, Sr-87/(86)Srm: 0.7062-0.7068, and epsilon Hf-(t): -43 to -9.7;and Brasilandia pluton, U-Pb age: 581 +/- 11 Ma, epsilon Nd-(t): -8.2 to -10.2, Nd T-DM ages: 1.63-1.68 Ga, Sr-87/(86)Srm0.7088-0.7112, epsilon Hf-(t)(:)-12.3 to -14.9), followed by late granodioritic intrusions (e.g., Guarataia pluton, U-Pb age: 576 +/- 9 Ma, epsilon Nd-(t): -12.52 to -13.11, Nd TOM age: 1.74-2.06 Ga, Sr-87/(86)Srm: 0.7104-0.7110, epsilon Hf-(t): -12.9 to -21.6). The Muriae batholith (U-Pb age: 620-592 Ma, epsilon Nd-(t): -8.2 to -13.6, Nd T-DM age: 1.41-1.88 (Ga) and the Conceicao 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 Bolivia and Marceleza complexes, making the link between the Aracuai and Ribeira orogenic domains. We suggest three phases of arc development: i) eastward migration of arc front (632-605 Ma), ii) widespread magma production in the whole arc (605-585 Ma), and iii) late plutonism in the western arc region (585-575 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. (C) 2015 Elsevier Ltd. All rights reserved.