New Tonian-Ediacaran zircon U-Pb ages and Hf isotopes from arc-related magmatism with adakite-like signatures in the Araçuaí-Ribeira Orogenic System (SE-Brazil): Implications for early Western Gondwana assembly

• AROS records Tonian and Cryogenian magmatic stages (Serra da Prata, Rio Negro) • Tonian (882–829 Ma) high-silica adakite-like show juvenile mantle isotopic signatures. • Cryogenian-Ediacaran (640–609 Ma) C-type adakite-like record crustal contamination. • Earliest records of subduction-related magmatism at the AROS. • Results link Western Gondwana amalgamation to recurrent subduction. Arc-related rocks preserved in Neoproterozoic orogenic belts provide key evidence for Precambrian subduction and plate-tectonic-style processes. Within the Neoproterozoic-Cambrian Araçuaí-Ribeira Orogenic System (AROS, SE-Brazil), two major arc systems are recognized. The Inner Magmatic Arc System (IMAS) is characterized by a short-lived Cordilleran-type magmatic arc, while the Outer Magmatic Arc System (OMAS) records two distinct evolutionary stages: Tonian juvenile Serra da Prata stage, and a Cryogenian-Ediacaran Cordilleran Rio Negro stage. We present new geochemical and geochronological data from orthogneisses at the northern termination of the OMAS within the AROS. Whole-rock geochemistry, Sm–Nd and Sr isotopes, and zircon U–Pb and Hf data reveal two distinct magmatic stages. Samples showing high-silica adakite-like (HSA) affinities yield Tonian ages (892 ± 28 to 829 ± 11 Ma), corresponding to the Serra da Prata stage. In contrast, samples displaying C-type adakite-like affinities and Cryogenian–Ediacaran ages (640 ± 7 to 609 ± 2 Ma), and are related to the Rio Negro stage. The Tonian HSA-adakite-like samples display juvenile, mantle-derived isotopic signatures (εNd t = +3.2 to +5.8; zircon εHf t = +12.2 to +9.9), indicating limited crustal involvement and signatures compatible with partial melting of young, hot oceanic lithosphere. In contrast, the Cryogenian samples with C-type adakite-like affinity show more evolved isotopic compositions (εNd t = −10.1 to −5.3; zircon εHf t = −11.6 to −2.4), suggesting contributions from lower-crustal sources and/or metasomatized mantle. These results support a two-stage evolution model for the OMAS: (1) early subduction of young oceanic lithosphere forming a primitive intra-oceanic arc (Serra da Prata), and (2) subsequent development into a more mature arc (Rio Negro), analogous to the modern Japanese arc system and related to crustal thickening, ridge subduction, or slab break-off. The preservation of Tonian and Ediacaran arc-related rocks in the AROS records recurrent convergent margins during the Neoproterozoic and highlights the critical role of juvenile crustal accretion in Gondwana assembly. The temporal and compositional correlations between the OMAS and other juvenile Neoproterozoic belts reinforce that Western Gondwana amalgamation involved multiple subduction and collision episodes, recording over 200 Myr of episodic events of subduction process around its cratonic nuclei.