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：

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新发现的古生代 Dacaotan 复合混合带的结构解剖：对中亚造山带西南部北天山洋俯冲-增生过程的影响


北天山带在中亚西南部造山带中占据着关键的地质位置，是揭示北天山洋长期演化历史的理想地点。然而，天山洋盆地如何以及何时最终被吞噬和关闭仍存在很大争议。为了解决这些问题，我们在这里对北天山带 Dacaotan 复合混合带的不同岩石-构造组合进行了全面调查。使用详细的地质测绘、结构分析、岩石关联以及新的地球化学和地质年代学数据，我们将 Dacaotan 复合混合带分为三个岩石构造组合：（1） 南部沉积前弧（约 423-398 马）组合，其特征是相对连贯和层理良好的 flysch 序列;（2） 中央俯冲带型蛇绿岩混合组合（约 468-461 马），由岩石成因相连的上地幔和海洋地壳成分组成，它们以蛇纹岩和沉积基质内的构造切片或块状形式暴露出来;（3） 北部增生的海洋板块地层混合组合（约 448-398 马），由散布在沙质至泥质基质中的增生沟槽填充浊积岩、海山（类似 OIB 的基岩）和海底岩石（类似 MORB 的基岩）组成。后运动学冥王星和岩脉揭示了最后的增生事件在约371 马之前完成。结合不同岩石构造组合的时空构型，我们得出结论，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，北天山洋流域的最终消耗发生在最新泥盆世之前，导致天山中部区块和北天山带之间沿着 Kanggguertag-Dacantao 复合混合带形成最终缝合线。