Abstract The Tonian Serra da Prata magmatic arc is part of an association of several magmatic arcs of the Ribeira orogenic system in Southeastern Brazil. Along with the Cryogenian Rio Negro arc, the Serra da Prata arc represents an intra-oceanic arc system while the Ediacaran Rio Doce arc represents an active continental margin arc. Here, we characterize the northernmost segment of the Serra da Prata arc, based on lithochemical and isotopic (whole-rock Sm-Nd and Rb-Sr, and zircon U-Pb and Lu-Hf) data from the Caxixe batholith, located in Espirito Santo State. The Caxixe batholith mostly consists of granodioritic to granitic and minor tonalitic to gabbroic rocks, with calc-alkaline, metaluminous to slightly peraluminous, magnesian, I-type signature and magmatic arc affinity. The rocks display LREE enrichment, positive to slightly negative Eu and negative Nb-Ta anomalies. Zircon U-Pb (LA-ICP-MS and SHRIMP) data reveal magmatic crystallization ages from 859±7 Ma to 847±8 Ma (for zircon cores) and a probably metamorphic age of 834±9 Ma (for zircon rims). Hf Isotopic data yield positive eHf(t) values between +10 and +14, and TDM Hf model ages from 1.01 Ga to 0.84 Ga, in agreement with whole-rock Nd and Sr data, with eNd(t) values from +0.9 to +6.4and TDM Nd model ages between 1.2 Ga and 0.8 Ga, and 87Sr/86Sr(i) of 0.6979-0.7035. Our data characterize a juvenile magmatic arc with striking mantle contribution, formed on a supra-subduction intra-oceanic setting similar to modern island arcs. As a whole, the Serra da Prata juvenile arc points to a large ocean that underwent intra-oceanic subduction in the Early Tonian. As a corollary, the Angola, Congo – Sao Francisco and Paranapanema paleocontinental blocks should be far from each other during the Early Tonian, separated by that large ocean. In a broad scenario, involving ophiolites and juvenile arcs of southern and central Brazil, several cratons of Western Gondwana once had been parts of paleocontinental pieces separated by very extensive Tonian-Cryogenian oceanic realms, including the Neoproterozoic Goias–Pharusian and Adamastor oceans.

中文翻译：

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Tonian Island Arc Remnants in the Northern Ribeira Orogen of Western Gondwana: The Caxixe Batholith (ESPÍRITO SANTO, SE BRAZIL)

摘要 Tonian Serra da Prata 岩浆弧是巴西东南部里贝拉造山系统几个岩浆弧组合的一部分。与 Cryogenian Rio Negro 弧一起，Serra da Prata 弧代表一个洋内弧系统，而 Ediacaran Rio Doce 弧代表一个活跃的大陆边缘弧。在这里，我们根据位于 Espirito 的 Caxixe 基岩的岩石化学和同位素（全岩 Sm-Nd 和 Rb-Sr，以及锆石 U-Pb 和 Lu-Hf）数据表征了 Serra da Prata 弧的最北段圣州。Caxixe 基岩主要由花岗闪长岩至花岗质和次要调质岩至辉长岩组成，具有钙碱性、金属铝质至微过铝质、镁质、I 型特征和岩浆弧亲和性。岩石显示 LREE 富集，正到微负的 Eu 和负的 Nb-Ta 异常。锆石 U-Pb（LA-ICP-MS 和 SHRIMP）数据显示岩浆结晶年龄从 859±7 Ma 到 847±8 Ma（对于锆石核）和可能的变质年龄为 834±9 Ma（对于锆石边缘）。Hf 同位素数据在 +10 和 +14 之间产生正 eHf(t) 值，TDM Hf 模型年龄从 1.01 Ga 到 0.84 Ga，与全岩 Nd 和 Sr 数据一致，eNd(t) 值从 +0.9 到+6.4 和 TDM Nd 模型年龄介于 1.2 Ga 和 0.8 Ga 之间，87Sr/86Sr(i) 为 0.6979-0.7035。我们的数据表征了具有惊人地幔贡献的幼年岩浆弧，形成于类似于现代岛弧的超俯冲洋内环境。总的来说，Serra da Prata 幼年弧指向一个大洋，它在托尼阶早期经历了洋内俯冲。作为推论，安哥拉，刚果-圣弗朗西斯科和帕拉纳帕内马古大陆块在托尼阶早期应该彼此远离，被那片大洋隔开。在涉及巴西南部和中部蛇绿岩和幼年弧的广泛情况下，冈瓦纳西部的几个克拉通曾经是古大陆碎片的一部分，被非常广泛的托尼亚-低温纪海洋领域分隔开来，包括新元古代戈亚斯-法鲁斯和阿达马斯托大洋。