Abstract The main site and timing of the final closure of the middle segment of the Paleo-Asian Ocean (PAO) has been an issue of hot debate, which hampers us from better understanding the late-stage tectonic evolution of the Central Asian Orogenic Belt (CAOB). Synthesizing the available geological records for the ophiolitic melanges in the Beishan Orogenic Belt (BOB), we regard the Liuyuan ophiolitic melange as the main site of the final closure of the middle segment of the PAO. To determine the final closure time of the middle segment of the PAO, this study mainly applied field-based, systematic zircon U-Pb-Hf isotopic analyses for the Carboniferous and Permian sedimentary successions on the northern and southern sides of the Liuyuan ophiolitic melange. Our results indicate that the late Carboniferous sedimentary successions north of the Liuyuan melange consisting mainly of interbedded sandstone and siltstone with minor conglomerate show primarily affinity with a local, single source, i.e. the constituent units of the BOB north of the Liuyuan melange. They were closely associated with the northward subduction of the middle segment of the PAO. By contrast, the unconformably overlying Permian clastic deposition on both sides of the Liuyuan ophiolitic melange shows comparable lithology that fines from a thick sequence of conglomerate at the base to thin-bedded turbidite sequences up section. These Permian units were probably deposited in a progressively deepening basin within an extensional post-collision regime after the disappearance of the middle segment of the PAO. All the

中文翻译：

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碎屑锆石物源对古亚洲洋中段最终闭合的制约

摘要 古亚洲洋（PAO）中段最终闭合的主要地点和时间一直是争论的热点问题，这阻碍了我们更好地了解中亚造山带晚期构造演化（ CAOB）。综合北山造山带（BOB）蛇绿混杂岩的现有地质记录，我们认为柳园蛇绿混杂岩是PAO中段最终闭合的主要地点。为了确定PAO中段的最终闭合时间，本研究主要对柳园蛇绿混杂岩北侧和南侧石炭纪和二叠纪沉积层序进行了基于现场的系统锆石U-Pb-Hf同位素分析。我们的研究结果表明，柳园混杂岩以北的晚石炭世沉积层序主要由砂岩和粉砂岩夹层和少量砾岩组成，主要与当地的单一来源，即柳园混杂岩以北的 BOB 的组成单元有亲缘关系。它们与 PAO 中段向北俯冲密切相关。相比之下，柳园蛇绿混杂岩两侧不整合上覆的二叠纪碎屑沉积显示出类似的岩性，从底部的厚砾岩层序到上部的薄层浊积岩层序细化。在 PAO 中段消失后，这些二叠纪单元可能沉积在伸展后碰撞区域内逐渐加深的盆地中。所有 单一来源，即六源混杂岩以北BOB 的组成单元。它们与 PAO 中段向北俯冲密切相关。相比之下，柳园蛇绿混杂岩两侧不整合上覆的二叠纪碎屑沉积显示出类似的岩性，从底部的厚砾岩层序到上部的薄层浊积岩层序细碎。在 PAO 中段消失后，这些二叠纪单元可能沉积在伸展后碰撞区域内逐渐加深的盆地中。所有 单一来源，即柳园混杂岩以北BOB 的组成单元。它们与 PAO 中段向北俯冲密切相关。相比之下，柳园蛇绿混杂岩两侧不整合上覆的二叠纪碎屑沉积物显示出类似的岩性，从底部的厚砾岩层序到上部的薄层浊积岩层序。在 PAO 中段消失后，这些二叠纪单元可能沉积在伸展后碰撞区域内逐渐加深的盆地中。所有 柳园蛇绿混杂岩两侧不整合上覆的二叠纪碎屑沉积显示出类似的岩性，从底部的厚砾岩层序到薄层浊积岩层序向上段。在 PAO 中段消失后，这些二叠纪单元可能沉积在伸展后碰撞区域内逐渐加深的盆地中。所有 柳园蛇绿混杂岩两侧不整合上覆的二叠纪碎屑沉积显示出类似的岩性，从底部的厚砾岩层序到薄层浊积岩层序向上段。在 PAO 中段消失后，这些二叠纪单元可能沉积在伸展后碰撞区域内逐渐加深的盆地中。所有