塔里木克拉通上元古界和下古生界碎屑锆石物源示踪及其对冈瓦纳大陆重建的意义

Due to the paucity of key geological evidence, controversy has long surrounded the paleogeographic-position and tectonic evolution of the Tarim Craton through late Neoproterozoic to early Paleozoic time, during which the Gondwana continent evolved into its final amalgamation stage. Neoproterozoic and early Paleozoic strata occur widely on the Tarim Craton and provide an ideal target for sedimentary provenance studies, since our preliminary data analysis has revealed a major provenance transition during this period. This proposal focuses on the Kepingtage, Kuluketage and Tiekelike regions in the Tarim Craton and plans to carry out systematic sedimentological investigation and detrital zircon provenance analyses on these sedimentary rocks. Tectonic settings during sedimentary deposition will be determined on the basis of the modal detrital content and whole-rock geochemical analyses. Paleocurrent direction data collected from the field are combined with U-Pb dating results of detrital zircons to precisely constrain the age of the provenance transition. Zircon hafnium and oxygen isotopes will be determined and linked to age data to reveal subduction and accretion processes at depth. Through a comprehensive comparison between detrital zircon data and magmatic, metamorphic and structural data, this study aims to constrain the paleogeographic-position of the Tarim Craton with respect to Gondwana in the early Paleozoic, the amalgamation time between them, and the tectonic history of the Proto-Tethys Ocean. This project could potentially generate new insights and ideas in understanding the coupling between the amalgamation of mega-continent and the subduction initiation along the continent’s peripheral margin.

因缺乏关键地质证据，塔里木克拉通在新元古代晚期至早古生代冈瓦纳大陆最终拼合阶段的相对古位置和演化历史存在诸多争议。上元古界和下古生界地层在塔里木克拉通较为发育，初步分析表明沉积物源在此阶段曾发生明显的转变，是开展物源示踪和古陆块重建的理想对象。项目拟以塔里木柯坪塔格、库鲁克塔格和铁克里克一带为主要研究区，对新元古代晚期和早古生代沉积岩开展系统的沉积学和碎屑锆石物源分析工作。通过碎屑组分统计和全岩地球化学测试判定沉积大地构造背景。依据野外古水流方向统计和碎屑锆石U-Pb年代学分析，更加准确地限定沉积物源变化的规律和时间，结合锆石Hf和O同位素特征反演俯冲增生的深部过程。通过对碎屑锆石数据与岩浆、变质、构造等资料的广泛对比，约束早古生代塔里木克拉通与冈瓦纳大陆的相对位置、二者的拼合时间以及原特提斯洋的演化历史，为深入理解大陆碰撞拼合与周缘俯冲增生事件的耦合关系提供新的线索和思路。

新元古代晚期至早古生代时期是冈瓦纳大陆主体部分最终碰撞拼合的时期，也是全球构造体制与表生环境转换的关键阶段，然而中国各陆块，特别是塔里木克拉通与冈瓦纳大陆的相对古地理位置和演化历史仍存在诸多争议。项目组成员围绕这些科学问题对塔里木克拉通周缘广泛发育的新元古界-下古生界地层和岩浆岩开展了野外地质调查、沉积物源分析、构造解析、地球化学、同位素年代学和古地磁学等综合研究并取得了一系列研究进展，其中最重要的研究进展包括：（1）重建了东亚陆块群在罗迪尼亚（Rodinia）、冈瓦纳（Gondwana）和潘基亚（Pangea）超大陆演化中的古地理位置；（2）在阿尔金造山带识别出Mariana型初始俯冲蛇绿岩，探讨了其对冈瓦纳大陆聚合期间全球板块构造体制与表生环境转换的重要指示意义；（3）根据对塔里木和天山造山带的研究，提出“受地幔柱改造的碰撞造山作用”新大地构造模式；（4）通过对阿尔金造山带的构造解析，揭示出中生代构造活动对青藏高原地壳结构的控制意义；（5）限定了塔里木克拉通在罗迪尼亚超大陆和冈瓦纳大陆中的位置，并探讨了其大地构造演化历史；（6）厘定出原特提斯洋西昆仑段经历了双向俯冲并最终闭合于430-420 Ma；（7）通过古地磁证据进一步限定了古亚洲洋的闭合过程与时间；（8）定量化约束了全球碎屑锆石记录和大地构造背景之间的联系。这些研究成果约束了塔里木克拉通在冈瓦纳大陆中的古地理位置及其演化历史，为深入理解大陆碰撞拼合与周缘俯冲增生事件的耦合关系、为揭示全球构造体制转换时间与过程提供了原创性的线索和思路。这些研究进展体现在项目组成员在过去五年内所发表的39篇SCI论文（其中25篇为课题第一标注，6篇为Nature Index检索论文）。