The evolution of the Meso-Tethys Ocean has received much research attention, but whether there was intra-oceanic and the starting time of subduction remains controversial. In this study, we present detailed petrological, U-Pb geochronology, geochemical, and Sr-Nd isotope investigations on Yurongguo ultramafic rocks from the western part of the Shiquanhe-Lagkor-Jiali suture zone, south of the Bangong-Nujiang suture zone, including harzburgites and websterites. The harzburgites are characterized by V-shaped REE patterns and significant Eu depletion, showing significant sediment influence. The websterites are classified into two groups based on their petrological and geochemical, but they all show distinctly Nb-Ta enrichment. Yurongguo ultramafic rocks have low Sr/Sr(t) but high εNd(t) values (+4.84 to + 8.55), indicating that these rocks evolved from a depleted mantle without the influence of arc. The zircon U-Pb age group includes 640 ± 30 Ma, 805 ± 13 Ma, 1002 ± 17 Ma, and 1781 ± 40 Ma, similar to the Precambrian basement of the central Lhasa subterrane. The harzburgites are the remnant of ∼ 30 % partial melting of the depleted mantle and metasomatized by a small amount of sediment melt. The websterites I are a cumulation of depleted mantle melt followed by metasomatized with Nb-Ta-rich material. The websterites II are the result of the reaction between the websterites I and sediment melt. Combined with previous studies, we proposed that these rocks may have formed during initial intra-oceanic subduction, which are the product of the early Jurassic subduction of the Meso-Tethys Ocean. The ancient continental basement of central Lhasa subterrane impacted the Early Jurassic igneous rock formed in the Bangong-Nujiang Tethys Ocean.

中文翻译：

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玉荣国蛇绿岩演化重建：对班公-怒江特提斯洋向南洋内俯冲的制约

中特提斯洋的演化备受研究关注，但是否存在洋内以及俯冲起始时间仍存在争议。在这项研究中，我们对班公-怒江缝合带以南狮泉河-拉格尔-加里缝合带西部的玉荣国超镁铁质岩石进行了详细的岩石学、U-Pb年代学、地球化学和Sr-Nd同位素研究，包括哈茨山岩和韦氏岩。方辉橄榄岩具有V型稀土分布特征和显着的Eu损耗，显示出显着的沉积物影响。根据岩石学和地球化学的不同，网沸石可分为两类，但它们都表现出明显的 Nb-Ta 富集。玉荣国超镁铁质岩石的Sr/Sr(t)值较低，但εNd(t)值较高(+4.84～+8.55)，表明这些岩石是由贫化地幔演化而来，没有受到弧的影响。锆石U-Pb年龄组包括640±30Ma、805±13Ma、1002±17Ma和1781±40Ma，与拉萨地中部的前寒武纪基底相似。方辉橄榄岩是贫化地幔约 30% 部分熔融的残余物，并被少量沉积物熔融交代。网背岩 I 是贫化地幔熔体的累积物，随后与富铌钽物质交代。韦氏石 II 是韦氏石 I 与沉积物熔体之间反应的结果。结合前人研究，我们提出这些岩石可能是在最初的洋内俯冲过程中形成的，是早侏罗世中特提斯洋俯冲的产物。拉萨中部地下的古老大陆基底撞击了班公怒江特提斯洋中形成的早侏罗世火成岩。