Abstract The Rio Doce magmatic arc, developed from ca. 630 to ca. 580 Ma on an active continental margin, linking the Aracuai and Ribeira orogens in southeastern Brazil. The arc plutonic portion comprises the G1 supersuite, a calc-alkaline, magnesian, I-type pre-collisional rock-assemblage, mostly composed of tonalite to granodiorite, frequently containing dioritic to mafic enclaves, and their metamorphosed equivalents. We carried out field, petrographic, lithochemical and isotopic (Sm–Nd and Sr) studies on a segment of the Rio Doce arc located in the transition region between the Aracuai and Ribeira orogens. The studied samples include metamorphozed granitic rocks (referred to by their igneous names in the QAP diagram), consisting of syenogranite, monzogranite, granodiorite, tonalite, quartz diorite, orthopyroxene-bearing tonalite and orthopyroxene-bearing quartz diorite. This rock assemblage defines an I-type, magnesian, metaluminous to slightly peraluminous, medium-to high-K, expanded calc-alkaline series. The numerous mafic to dioritic enclaves and related features indicate magma mixing processes. Isotopic data show moderately to strongly negative eNd(t) values (−2.9 to −13.6) and intermediate to high 86Sr/87Sr ratios (0.7067–0.7165) suggests assimilation of older crustal material (i.e., the Juiz de Fora and Pocrane complexes, enclosing paragneisses), which is also indicated by Nd TDM model ages from 1.19 Ga to 2.13 Ga. Magmatic orthopyroxene and high content of CaO in garnet suggest magma crystallization in the deep crust. Together, our data point out to a combination of partial melting of mantle wedge in the subduction zone, deep crustal anatexis, host rock assimilation, and crystal fractionation for magma genesis in the southeastern Rio Doce arc.

中文翻译：

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巴西东南部阿拉索伊-里贝拉边界段的埃迪卡拉里约多西岩浆弧：岩石化学和同位素（Sm-Nd 和 Sr）特征

摘要 里约多西岩浆弧，从大约发展。630 到大约 580 Ma 位于活动大陆边缘，连接巴西东南部的 Aracuai 和 Ribeira 造山带。弧深成岩部分包括 G1 超组，一种钙碱性、镁质、I 型碰撞前岩石组合，主要由闪长岩到花岗闪长岩组成，经常包含闪长岩到镁铁质飞地，以及它们的变质等价物。我们对位于 Aracuai 和 Ribeira 造山带之间过渡区的 Rio Doce 弧段进行了野外、岩相学、岩石化学和同位素（Sm-Nd 和 Sr）研究。研究的样品包括变质花岗岩（在 QAP 图中以其火成岩名称表示），由正长花岗岩、二长花岗岩、花岗闪长岩、闪长岩、石英闪长岩、含斜方辉石的闪长岩和含斜方辉石的石英闪长岩。这种岩石组合定义了 I 型、镁质、金属铝质至微铝质、中至高 K、扩展钙碱性系列。大量的镁铁质至闪长岩飞地和相关特征表明岩浆混合过程。同位素数据显示中度至强负的 eNd(t) 值（-2.9 至 -13.6）和中至高的 86Sr/87Sr 比率（0.7067-0.7165）表明旧地壳物质（即 Juiz de Fora 和 Pocrane paragneisses），这也由 Nd TDM 模型表明年龄从 1.19 Ga 到 2.13 Ga。岩浆斜方辉石和石榴石中高含量的 CaO 表明深地壳中的岩浆结晶。总之，我们的数据表明俯冲带地幔楔部分熔化的组合，