Juvenile contribution of the Neoproterozoic Rio Negro Magmatic Arc (Ribeira Belt, Brazil): Implications for Western Gondwana amalgamation Miguel Tupinambá a, ⁎, Monica Heilbron a , Claudio Valeriano a , Rubem Porto Júnior a, b , Fátima Blanco de Dios a, c, d , Nuno Machado e, 1 , Luiz Guilherme do Eirado Silva a , Júlio Cesar Horta de Almeida a a TEKTOS, Geotectonics Research group, UERJ Rio de Janeiro State University, Rua S. Francisco Xavier, 524/4006-A. Rio de Janeiro RJ, Brazil 20550-900 b Petrology research group, Universidade Federal Rural do Rio de Janeiro. Instituto de Agronomia, Departamento de Geociências. BR-465, Km 7. Seropédica. Rio de Janeiro RJ Brazil 23890-000 c Petróleo Brasileiro SA, PETROBRAS. Av. República do Chile d Petróleo Brasileiro SA, PETROBRAS., 330/24th Torre Leste Rio de Janeiro RJ Brazil 20031–170 e GEOTOP, Université du Québec à Montréal, Canada abstract article info Article history: Received 4 January 2011 Received in revised form 3 May 2011 Accepted 16 May 2011 Available online 6 June 2011 Keywords: Western Gondwana Ribeira belt Neoproterozoic Magmatic arc Tectonics The ca. 790–600 Ma Rio Negro Complex (RNC) of the Ribeira belt (Brazil) consists of a plutonic portion of a magmatic arc built by the E-vergent subduction of the ESE border of the São Francisco paleoplate during the amalgamation of Western Gondwana. The plutonic series comprises low- to medium-K granitoids (ca. 790–620 Ma) and high-K granitoids and shoshonite rocks (ca. 610–605). The age span of 185 m.y. is suggestive of a long history of arc-related magmatism, continuously or not in time. The Nd isotopic signatures of the RNC consist of εNd(t) ratios from -3 to + 5 for the medium-K series shoshonite series and from -14 to -3 for the younger high-K group. This time-dependent trend of Nd isotopes is indicative of progressive maturity of the arc over time. The same evolution is indicated by Sr data, as the medium-K rocks have 87 Sr/ 86 Sr initial ratios b 0.705 while the high-K rocks yield values between 0.705 and 0.710. The predominance of intermediate rocks over mafic ones suggests an initial intra-oceanic to transitional stage, possibly developed in a distal portion of a passive margin, such as the Japanese arc, evolving to a more developed, differentiated felsic rock associations. The role of transform fault zones, such as the Luanda shear zone, is emphasized in order to explain the consumption of a wide oceanic plate in the inner portion of Western Gondwana. © 2011 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. 1. Introduction At the onset of Western Gondwana amalgamation, east-verging subduction was in course along the eastern and southern margins of the São Francisco–Congo proto-continent (Ribeira and Araçuaí belts) and along the western margin (Coastal terrane) of the Angola-Kasai paleo-plate, presently in the Kaoko Belt (Heilbron et al. 2008; Babinski et al., 2011; Tohver et al., 2011). The active margin and the arc-related rocks of this episode are well preserved both in the Ribeira belt and in the Coastal terrane of Africa. The Ribeira belt (Fig. 1) extends for almost 1400 km along the Atlantic coast of SE-Brazil (Almeida et al., 1981; Campos Neto, 2000; Trouw et al., 2000; Heilbron et al., 2000, 2004a,b, 2008). Its African counterpart, in Angola and Namibia, is represented from north to south by the West Congo belt, the Angola craton and the Kaoko belt (Goscombe et al., 2003, 2005a,b; Gray et al., 2006; Goscombe and Gray, 2007, 2008). Rio Negro Complex is the plutonic portion of a 790–600 Ma magmatic arc (foliated tonalites, granodiorites, granites and gabbros) that presently crops out in the central segment of the Ribeira Belt (Tupinambá et al., 2000a; Heilbron and Machado 2003). The Rio Negro Arc is located in the central portion of western Gondwana between large cratonic blocks (Fig. 1). Despite the internal location within the agglutinating supercontinent, subduction of a large oceanic lithospheric plate is suggested by great longitudinal extension and protracted history (Heilbron and Machado, 2003; Heilbron et al., 2008). Gondwana Research 21 (2012) 422–438 ⁎ Corresponding author at: Faculdade de Geologia, UERJ. Universidade do Estado do Rio de Janeiro, R. S. Francisco Xavier, 524 s. A4016. Maracanã. Rio de Janeiro RJ, Brazil 20550–900. Tel.: +55 21 2334 0533#210; fax: +55 21 2334 0533#214. E-mail addresses: tupi@uerj.br, tupinambamiguel@gmail.com (M. Tupinambá). 1 In memoriam. 1342-937X/$ – see front matter © 2011 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.gr.2011.05.012 Contents lists available at ScienceDirect Gondwana Research journal homepage: www.elsevier.com/locate/gr