New UePb ages and lithochemical attributes of the Ediacaran Rio Doce magmatic arc, Araçuaí confined orogen, southeastern Brazil Leonardo Gonçalves a, * , Federico Farina a , Cristiano Lana a , Antônio C. Pedrosa-Soares b , Fernando Alkmim a , Hermínio A. Nalini Jr. a a Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro, Morro do Cruzeiro, 35400-000 Ouro Preto, MG, Brazil b Universidade Federal de Minas Gerais, CPMTC-IGC-UFMG, Av. Antônio Carlos 6627, Pampulha, 31270-901 Belo Horizonte, MG, Brazil article info Article history: Received 30 July 2013 Accepted 18 February 2014 Keywords: G1 supersuite Rio Doce arc Rhyacian basement Araçuaí-West Congo orogen abstract The 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, sug- gesting 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) enclave- rich 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 per- aluminous, 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 HT- melting of granulitic (H 2 O-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. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The Araçuaí orogen (SE Brazil) and its counterpart located in Africa, the West Congo belt, represent a branch of the Brasiliano e Pan-African orogenic network (Fig. 1) formed during the amal- gamation of West Gondwanaland by the end of the Neoproterozoic (Trompette, 1994; Brito Neves et al., 1999). In contrast to typical plate margin orogens, the Araçuaí e West Congo orogenic system developed inside an embayment of the São Francisco-Congo palaeocontinent, i.e., a gulf-like basin, partially floored by ocean crust and connected to the Adamastor Ocean (Pedrosa-Soares et al., 1992, 1998, 2001, 2008; Cordani et al., 2003; Alkmim et al., 2006). Such a peculiar geotectonic scenario, together with the occurrence of ophiolites and a pre-collisional magmatic arc, inspired the concept of a confined orogen (Pedrosa-Soares et al., 2001), as an intermediate term between the typical continental margin or intercratonic orogens, and the wholly ensialic intracontinental orogens or inverted aulacogens (Rogers and Santosh, 2004). Despite this confined environment, the Araçuaí orogen shows a well-developed calc-alkaline magmatic arc, the Rio Doce arc, which occupies an area of over 20,000 km 2 (Figueiredo and Campos Neto, 1993; Nalini Jr. et al., 2005; Pedrosa-Soares and Wiedemann- Leonardos, 2000; De Campos et al., 2004; Martins et al., 2004; Gonçalves et al., 2010; Novo et al., 2010; Pedrosa-Soares et al., 2011). * Corresponding author. Tel.: þ55 31.87101840. E-mail addresses: leonardo@degeo.ufop.br, leonardogeologo@hotmail.com (L. Gonçalves), fannak@gmail.com (F. Farina), cristianodeclana@gmail.com (C. Lana), pedrosa@pq.cnpq.br (A.C. Pedrosa-Soares), ffalkmim@gmail.com (F. Alkmim), herminio.nalini@gmail.com (H.A. Nalini). Contents lists available at ScienceDirect Journal of South American Earth Sciences journal homepage: www.elsevier.com/locate/jsames http://dx.doi.org/10.1016/j.jsames.2014.02.008 0895-9811/Ó 2014 Elsevier Ltd. All rights reserved. Journal of South American Earth Sciences 52 (2014) 129e148