The Harihada–Chegendalai ophiolitic mélange, which is located between the Bainaimiao arc and the North China Craton, holds significant clues regarding the tectonic setting of the southern margin of the Central Asian Orogenic Belt. The ophiolitic mélange is mainly composed of gabbroic and serpentinized ultramafic rocks. Here, zircon U–Pb dating, in situ zircon Hf isotopic, whole-rock geochemical and in situ mineral chemical data from the ophiolitic mélange are reported. The zircons in the gabbroic rocks yielded concordia U–Pb ages of 450–448 Ma and exhibited slightly positive ϵHf(t) values (0.87–4.34). The geochemical characteristics of the gabbroic rocks indicate that they were generated from a mantle wedge metasomatized by subduction-derived melts from sediments with continental crust contamination, in a fore-arc tectonic setting. These rocks also experienced the accumulation of plagioclase. The geochemical characteristics of the ultramafic rocks and their Cr-spinels indicate that they may constitute part of residual mantle that has experienced a high degree of partial melting and has interacted with fluids/melts released from the subducted slab in the same fore-arc tectonic setting. The ophiolitic mélange may therefore have formed in this fore-arc tectonic setting, resulting from the northward subduction of the South Bainaimiao Ocean beneath the Bainaimiao arc during Late Ordovician time, prior to the collision between the Bainaimiao arc and the North China Craton during the Silurian to Carboniferous periods.

中文翻译：

---

白乃庙弧南缘晚奥陶世弧前蛇绿混杂岩：来自锆石U-Pb-Hf同位素和地球化学分析的制约

位于白乃庙弧与华北克拉通之间的Harihada-Chegendalai蛇绿混杂岩为中亚造山带南缘的构造环境提供了重要线索。蛇绿混杂岩主要由辉长岩和蛇纹岩化的超镁铁质岩组成。在这里，锆石 U-Pb 测年，原位锆石 Hf 同位素、全岩地球化学和原位报告了蛇绿混杂岩的矿物化学数据。辉长岩中的锆石产生了 450-448 Ma 的 concordia U-Pb 年龄，并表现出轻微的正ε氢氟酸(t) 值 (0.87–4.34)。辉长岩的地球化学特征表明，它们是在弧前构造环境中由受大陆地壳污染的沉积物俯冲衍生的熔体交代的地幔楔产生的。这些岩石也经历了斜长石的堆积。超镁铁质岩石及其Cr-尖晶石的地球化学特征表明，它们可能构成残余地幔的一部分，经历了高度的部分熔融，并与同一弧前构造背景下俯冲板片释放的流体/熔体相互作用. 因此，蛇绿混杂岩可能形成于这种弧前构造环境，是晚奥陶世时期南百乃庙洋向北俯冲到百乃庙弧之下的结果，