Abstract Unravelling the complexity of tonian-cryogenian (950-680 Ma) evolution of ophiolites requires the search for rare mineral systems and their quantification with varied techniques. Ophiolites in the Brasiliano Orogen are widely distributed over 2,000 km along the eastern half of South America. We selected two ophiolites from different geotectonic settings of the Sul-Riograndense Shield, southern Brasiliano Orogen, to delimit the evolution of the oceanic phase of the orogen. The southern portion of the Bossoroca ophiolite is inserted in the Sao Gabriel juvenile terrane and contains rare metasomatic tourmaline in chloritite close to serpentinite and metamorphosed Cr-spinel. The southern Bossoroca ophiolite was intruded by Cerro da Cria and Ramada Granites and the U-Pb-Hf isotopic study of zircon from these rocks constrains the crustal evolution of the Sao Gabriel juvenile terrane. Capane ophiolite has similar age (793-715 Ma) as the Bossoroca ophiolite and was inserted in the Porongos fold-thrust belt with preserved Cr-spinel of mantellic composition. Integrated use of Cr-spinel mineral chemistry, B isotopes in tourmaline in the Bossoroca ophiolite and zircon U-Pb-Hf isotopes of granites associated with the southern Bossoroca ophiolite revealed several steps in the evolution of the ophiolites in the Dom Feliciano Belt. Capane Cr-spinel cores have mantle-derived compositions (Mg# 0.66 – 0.69; Cr# 0.51 – 0.53), tourmaline from the Bossoroca ophiolite is dravite and has δ11B = 0 to +3, and granites crystallization ages are 578 ± 3.2 and 612 ± 12 Ma (eHfzrn = -10 to -25). Zircon from other dravite occurrences of the Bossoroca ophiolite were previously dated at 920 Ma. We unraveled the main steps in the evolution of ophiolites from the southern Brasiliano Orogen, with emphasis on the Bossoroca and Capane ophiolites, during their trajectory from mid-ocean ridge (920 Ma), formation of dravite in oceanic crust, preservation of mantellic cores in Cr-spinel, and intrusion of craton-generated granites at 612-578 Ma.

中文翻译：

---

巴西利亚诺造山带南部托宁-低温蛇绿岩演化的海洋地壳和地幔证据

摘要 要解开蛇绿岩 tonian-cryogenian (950-680 Ma) 演化的复杂性，需要寻找稀有矿物系统并使用各种技术对其进行量化。巴西利亚诺造山带蛇绿岩沿南美洲东半部广泛分布超过 2,000 公里。我们从巴西利亚诺造山带南部 Sul-Riograndense Shield 的不同大地构造环境中选择了两种蛇绿岩，以划定造山带海洋阶段的演化。Bossoroca蛇绿岩的南部插入在Sao Gabriel幼年地体中，含有稀有的绿泥石中的交代碧玺，接近蛇纹石和变质铬尖晶石。南部 Bossoroca 蛇绿岩被 Cerro da Cria 和 Ramada 花岗岩侵入，这些岩石中锆石的 U-Pb-Hf 同位素研究限制了 Sao Gabriel 幼年地体的地壳演化。Capane蛇绿岩与Bossoroca蛇绿岩具有相似的年龄（793-715 Ma），并被插入Porongos褶皱逆冲带中，并保存着具有幔质成分的Cr-尖晶石。综合使用 Cr-尖晶石矿物化学、Bossoroca 蛇绿岩中电气石的 B 同位素和与南部 Bossoroca 蛇绿岩相关的花岗岩的锆石 U-Pb-Hf 同位素揭示了 Dom Feliciano 带蛇绿岩演化的几个步骤。Capane Cr-尖晶石核具有地幔衍生成分（Mg# 0.66 – 0.69；Cr# 0.51 – 0.53），来自 Bossoroca 蛇绿岩的电气石是水镁石，δ11B = 0 至 +3，花岗岩结晶年龄分别为 578±3.2 和 612±12 Ma（eHfzrn = -10 至 -25）。来自 Bossoroca 蛇绿岩的其他火成岩矿点的锆石先前的年代为 920 Ma。我们揭示了巴西利亚诺造山带南部蛇绿岩演化的主要步骤，重点是 Bossoroca 和 Capane 蛇绿岩，在它们从大洋中脊（920 Ma）的轨迹中，在大洋地壳中形成水辉石，在Cr-尖晶石和克拉通生成花岗岩在 612-578 Ma 的侵入。