The Mongol-Okhotsk suture belt represents the result of the final closure of the Mongol-Okhotsk Ocean between the Siberian Craton and Erguna Block (also called Amuria), which played an essential role in the formation and tectonic evolution of eastern Eurasia during Mesozoic times. However, the timing of the final closure and subduction polarity of the Mongol-Okhotsk Ocean are still debated. In this study, provenance analysis of Multidimensional scaling and crustal thickness variation based on zircon Eu anomaly were used for the first time to reveal the tectonic evolution of the Mongol-Okhotsk Ocean during Mesozoic times. The results show that the evolution of the Mongol-Okhotsk Ocean can be divided into several stages. From Early Triassic (∼245 Ma) onwards, the Mongol-Okhotsk Ocean started to shrink due to southward subduction beneath the Erguna Block. The closure of western segments of the Mongol-Okhotsk Ocean occurred in the Late Triassic, leading to a weakening or cessation of oceanic plate subduction, and the prevalence of an extensional environment during 225–215 Ma. Subsequently, after the Late Triassic (starting at ca. 205 Ma), subduction of the Mongol-Okhotsk Ocean continued until the middle segments closed during Middle Jurassic (∼165 Ma). From 165 to 155 Ma, many magmatic arc rocks and metamorphic core complexes formed in the central and western segments of the Mongol-Okhotsk suture belt within a post-orogenic extensional setting. The eastern part of the Mongol-Okhotsk Ocean rapidly closed in a scissor-like manner, resulting in the collision between the Erguna Block and the Siberian Craton during the Late Jurassic (∼150–145 Ma). Collision also caused uplift of the southern margin of the Siberian Craton and the sediment deposition in the Mohe Basin. The subsequent crustal shortening associated with the collision led to the formation of nappes and the emplacement of adakites along the northern margin of Greater Xing'an Mountains. Since the Early Cretaceous, the compressional environment transitioned into a post-orogenic extensional tectonic environment influenced by the west-directed slab rollback of the Paleo-Pacific Plate and detachment of the subducted Mongol-Okhotsk oceanic plate after closure of the Mongol-Okhotsk Ocean.

中文翻译：

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蒙古-鄂霍次克洋的性质和多阶段演化：漠河盆地沉积记录的新见解


蒙古—鄂霍茨克缝合带是西伯利亚克拉通与额尔古纳地块（又称阿穆里亚）之间蒙古—鄂霍茨克洋最终闭合的结果，对中生代欧亚大陆东部的形成和构造演化发挥了重要作用。然而，蒙古-鄂霍茨克洋最终闭合的时间和俯冲极性仍然存在争议。本研究首次利用基于锆石Eu异常的多维标度和地壳厚度变化的物源分析揭示了蒙古-鄂霍茨克洋中生代的构造演化。结果表明，蒙古-鄂霍次克洋的演化可分为几个阶段。从早三叠世（∼245 Ma）开始，由于额尔古纳地块向南俯冲，蒙古-鄂霍次克洋开始缩小。蒙古-鄂霍茨克洋西段的闭合发生在晚三叠世，导致大洋板块俯冲减弱或停止，并在 225-215 Ma 期间普遍存在拉张环境。随后，在晚三叠世（大约从 205 Ma 开始）之后，蒙古-鄂霍茨克洋继续俯冲，直到中侏罗世（∼165 Ma）期间中段闭合。 165至155Ma期间，蒙古-鄂霍茨克缝合带中西段在造山后伸展背景下形成了许多岩浆弧岩和变质核杂岩。蒙古-鄂霍茨克洋东部以剪刀状迅速闭合，导致晚侏罗世（∼150–145 Ma）额尔古纳地块与西伯利亚克拉通发生碰撞。碰撞还造成西伯利亚克拉通南缘隆起和漠河盆地沉积物沉积。 随后与碰撞相关的地壳缩短导致了推覆体的形成以及大兴安岭北缘埃达克岩的侵位。早白垩世以来，受古太平洋板块西向板块回滚和蒙古鄂霍茨克洋闭合后俯冲蒙古鄂霍茨克洋板块脱离的影响，挤压环境转变为造山后伸展构造环境。