Late Mesozoic exhumation of metamorphic core complexes from the Xiaoqinling to Dabie orogen, central China: a record of Paleo-Pacific slab rollback

A series of metamorphic core complexes, including the Xiaoqinling, Xiong’ershan, and Dabie Mountains, span from west to east within the Qinling-Dabie Orogen of Central China. Despite their similar formation timelines and tectonic trends, they exhibit distinct geochemical signatures and exhumation processes. In the Xiaoqinling region, magmatic source temperatures initially increase with depth from approximately 606°C, reaching a peak around 847°C, and then decrease to approximately 660°C at greater depths, whereas in the Xiong’ershan area, they consistently decrease (811→609°C). The Dabie Mountains show consistent source temperatures (~800°C) across depths, suggesting their location above the ‘kink’ of Late Mesozoic Pacific subduction mantle wedge. Multi-method thermochronological analysis indicates that from 139 Ma to 85 Ma, the Xiaoqinling region cooled at 15.1°C/Ma initially, followed by deceleration to 2.7°C/Ma. Similarly, the Xiong’ershan and Dabie Mountains experienced two-stage exhumation processes, with cooling rates of 10.2°C/Ma, 3.7°C/Ma, and 20.3°C/Ma, 3.2°C/Ma, respectively. High-angle subduction and rollback of the ancient Pacific Plate during the Jurassic–Cretaceous transition facilitated the formation and rapid exposure of these metamorphic core complexes. Subsequent Pacific subduction reorientation during the Late Cretaceous reduced regional extension and thereby decreased the uplift and exhumation rates of these complexes.

中国中部秦岭-大别造山带内自西向东展布有一系列变质核杂岩（metamorphic core complexes），包括小秦岭、熊耳山与大别山。尽管三者在形成时限与构造走向方面均具有相似性，却展现出截然不同的地球化学特征与折返过程。就小秦岭地区而言，其岩浆源区温度大致随深度变化：从约606℃开始升高，峰值达847℃左右，随后在更深部降至约660℃；而熊耳山地区的源区温度则持续降低（811℃→609℃）。大别山地区的源区温度在不同深度均保持一致（约800℃），这表明其位于晚中生代太平洋俯冲地幔楔的“拐点”上方。多方法热年代学分析结果显示，在139 Ma至85 Ma期间，小秦岭地区的冷却速率最初为15.1℃/Ma，随后减速至2.7℃/Ma。同理，熊耳山与大别山也经历了两阶段折返过程，其冷却速率分别为10.2℃/Ma、3.7℃/Ma与20.3℃/Ma、3.2℃/Ma。侏罗纪-白垩纪过渡期，古太平洋板块发生高角度俯冲与板片回撤，促进了这些变质核杂岩的形成与快速出露。晚白垩世时期，太平洋俯冲方向发生改变，使得区域伸展作用减弱，进而降低了这些杂岩的抬升与折返速率。