Abstract The southern region of the Espirito Santo State is located in the Aracuai-Ribeira Orogen System (AROS) limit, where neoproterozoic orthoderived rocks undergone metamorphism at high-grade condition exhibiting partial melting and deformation features. This study focuses on the Pre-collisional Opx-granitoids Unit that shows varied proportions of orthopyroxene and garnet. Petrographic, geochemical, geothermobarometric and U-Pb in zircon studies were carried out. We distinguished two mineral assemblages: (i) consisting of plagioclase, quartz, biotite, amphibole, orthopyroxene and ilmenite; and (ii) with plagioclase, quartz, orthoclase, biotite, amphibole, garnet and ilmenite. The former is related to the opx-metatonalite protolith and the latter to metamorphic paragenesis. The geochemical analyses of the Pre-collisional Opx-granitoids Unit reveal an arc-related environment, similar to the Rio Doce and Rio Negro - Serra da Prata Arcs defined in the Aracuai and Ribeira orogens, respectively. The temperature conditions obtained for assemblage (ii) were 670–860 °C (granulite facies) and pressure from 5.24 to 10.2 kbar. Four different intervals of concordant ages were yielded in the studied samples. The oldest age of 716 Ma is interpreted as related to the pluton emplacement (E1). The ages of 604 Ma and 595 Ma are associated with the same magmatic event (E2), and the magmatic age of 586 Ma (E3) indicates another magma injection event. The age of 574 Ma (E4) is related to a high-grade metamorphic event whose P-T conditions were obtained in assemblage (ii) from geothermobarometric calculations. These results confirm the extension of Rio Doce magmatic arc toward the south and establish a connection between Aracuai and Ribeira orogens.

中文翻译：

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巴西东南部 Araçuaí-Ribeira 造山带边界前碰撞 Opx-Metatonalite 的岩浆活动期和 PT 变质条件估计

摘要 圣埃斯皮里图州南部地区位于阿拉库艾-里贝拉造山带（AROS）界限内，新元古代正源岩在高品位条件下发生变质作用，表现出部分熔融变形特征。这项研究的重点是碰撞前 Opx-花岗岩单元，该单元显示了不同比例的斜方辉石和石榴石。进行了岩石学、地球化学、地热气压和锆石 U-Pb 研究。我们区分了两种矿物组合：(i) 由斜长石、石英、黑云母、角闪石、斜方辉石和钛铁矿组成；(ii) 斜长石、石英、正长石、黑云母、角闪石、石榴石和钛铁矿。前者与 opx-变质岩原岩有关，后者与变质共生有关。碰撞前 Opx-花岗岩单元的地球化学分析揭示了一个与弧相关的环境，类似于分别在 Aracuai 和 Ribeira 造山带中定义的 Rio Doce 和 Rio Negro - Serra da Prata 弧。组合 (ii) 获得的温度条件为 670-860 °C（麻粒岩相），压力为 5.24 至 10.2 kbar。在所研究的样本中产生了四个不同的一致年龄区间。最古老的 716 Ma 年龄被解释为与岩体侵位（E1）有关。604 Ma和595 Ma的年龄与同一岩浆事件（E2）有关，586 Ma（E3）的岩浆年龄表明另一个岩浆注入事件。574 Ma (E4) 的年龄与一个高等级变质事件有关，其 PT 条件是在组合 (ii) 中通过地温气压计算获得的。