The North Tianshan Belt occupies a pivotal geological position within the southwestern Central Asian Orogenic Belt, making it an ideal location to unravel the long-term evolutionary history of the North Tianshan Ocean. However, how, and when the Tianshan oceanic basin was finally consumed and closed remains highly debated. To resolve these questions, here, we conducted a comprehensive investigation of the different litho-tectonic assemblages of the Dacaotan composite mélange belt in the North Tianshan Belt. Using detailed geological mapping, structural analyses, rock associations, and new geochemical and geochronological data, we divide the Dacaotan composite mélange belt into three litho-tectonic assemblages: (1) the southern sedimentary forearc (ca. 423–398 Ma) assemblage that is characterized by relatively coherent and well-bedded flysch sequences; (2) the central supra-subduction zone-type ophiolitic mélange assemblage (ca. 468–461 Ma) consisting of petrogenetically linked upper mantle and oceanic crustal components, which are exposed as tectonic slices or blocks within a serpentinite and sedimentary matrix; and (3) the northern accreted ocean plate stratigraphy mélange assemblage (ca.448–398 Ma) that is composed of accreted trench-fill turbidites, seamounts (OIB-like basic rocks) and ocean floor rocks (MORB-like basic rocks) dispersed in a sandy to pelitic matrix. Post-kinematic pluton and dyke reveal that the final accretionary event was completed prior to ca. 371 Ma. In conjunction with the spatial–temporal configurations of the different litho-tectonic assemblages, we conclude that the North Tianshan Ocean underwent bi-directional subduction and intra-oceanic subduction events during the Early Paleozoic. Our findings suggest the final consumption of the North Tianshan Ocean basin occurred before the Latest Devonian, resulting in the formation of the ultimate suture between the Central Tianshan Block and the North Tianshan Belt along the Kanggguertag-Dacantao composite mélange belt.

中文翻译：

---

新认识的古生代大草滩复合混杂岩带的构造解剖：对中亚造山带西南部北天山洋俯冲-增生过程的启示


北天山带在中亚造山带西南部具有举足轻重的地质地位，是揭示北天山海洋长期演化历史的理想地点。然而，天山洋盆如何以及何时最终被消耗和关闭仍然存在激烈争论。为了解决这些问题，我们对北天山带大草滩复合混杂岩带的不同岩石构造组合进行了综合考察。利用详细的地质填图、结构分析、岩石组合以及新的地球化学和年代学数据，我们将大草滩复合混杂岩带分为三个岩石构造组合：(1) 南部沉积弧前组合（约 423–398 Ma），即以相对连贯且层理良好的复理石序列为特征； (2) 中央俯冲带上型蛇绿混杂岩组合（约 468–461 Ma），由岩石成因相关的上地幔和大洋地壳成分组成，这些成分以构造片或块体的形式暴露在蛇纹岩和沉积基质中； (3) 北部增生洋板块地层混杂岩组合（约 448–398 Ma），由分散的海沟充填浊积岩、海山（类 OIB 基性岩）和海底岩石（类 MORB 基性岩）组成。在沙质至泥质基质中。运动后的岩体和岩脉揭示了最终的吸积事件在大约 10 年前完成。 371 马。结合不同岩石构造组合的时空配置，我们认为北天山洋在早古生代经历了双向俯冲和洋内俯冲事件。 我们的研究结果表明，北天山洋盆的最终消耗发生在晚泥盆世之前，导致中天山地块和北天山带之间沿康古尔塔格-大坎套复合混杂岩带的最终缝合带形成。