库车坳陷东部依奇克里克剖面新生代磁性地层年代及其对南天山变形隆升过程的制约

Since the Early Cenozoic, the continental collision between India and Eurasia plates and the continuous northward penetration reactivated the ancient Tianshan Orogenic Belts. Consequently, the very thick continuous sediments developed in the basins distributed on the north and south sides of the Tianshan. These sediments document the evolution history of the Tianshan in Cenozoic and provide abundant materials for the study of Asian inland aridity, the uplift of the Tianshan and the paratethys evolution. However, as a key for the forgoing studies, the previous Cenozoic strata chronology studies were mainly limited in Neogene, and the dating results were also controversial. This fact severely hindered the understanding of uplift history of the Tianshan and its environment-resources effect. .The south limb of the Yiqikelike anticline, located at the piedmont of eastern Kuqa depression of the South Tianshan, preserved huge successive sediments sequence. Based on high resolution magnetostratigraphic study of these sediments, combined with biostratigraphic data, a complete and continuous Cenozoic chronostratigraphic sequence in Kuqa depression will be presented in this study. Then, significant tectonic events and their time sequences will be tried to captured through the studies on tectonic rotations, sedimentation rate and deposition facies. The above studies are critical to provide accurate chronological constraints and new tectonic evidences for the understanding of tectonic-climatic evolution history and deformation process of the Cenozoic South Tianshan.

新生代早期，印度板块与欧亚板块的碰撞及其持续向北推挤和楔入作用，使得天山这一古老造山带重新复活，并在山体南北两侧的盆地堆积了厚层沉积物，它们不仅记录了天山新生代构造演化历史，而且为深入理解天山隆升的资源环境效应、亚洲内陆干旱化以及副特提斯海演化等重大科学问题提供了丰富材料。然而，作为上述研究核心基础的新生代地层年代研究多限于新近纪以来、并且存在很大争议，严重束缚了对天山新生代构造隆升过程及其资源环境效应、气候变化等的认识。天山南麓库车坳陷东部山前依奇克里克背斜南翼发育了巨厚且较连续完整的新生代沉积序列，本项目拟对其进行高精度磁性地层学研究，结合生物地层学资料建立库车坳陷完整的新生代地层年代序列。再通过构造旋转、沉积速率和沉积相研究，捕获研究区重大构造变形事件及其时间序列，以期为合理解释和完善南天山新生代构造演化历史、变形过程及气候变化提供年代学约束和新的构造证据。

新生代以来，天山南麓库车坳陷堆积的巨厚沉积物为研究南天山构造演化、亚洲内陆干旱化以及副特提斯海进退等热点问题提供了良好载体。然而，作为解析上述构造事件、古气候演化等核心基础的地层年代在该区存在较大争议且多数研究限于新近纪以来。为此，本项目选择了库车坳陷东部山前依奇克里克背斜南翼发育的巨厚且较连续完整的新生代沉积序列开展高精度磁性地层学研究，结合剖面孢粉组合特征以及前人古生物年代学资料，本项目获得了剖面底部为~42.2 Ma以及顶部为~6.5 Ma的较长尺度年代序列，确定了库车坳陷库姆格列木群、苏维依组、吉迪克组、康村组和库车组的磁性地层年代分别为~42.2-38 Ma、38-36 Ma、36-13 Ma、13-6.5 Ma和< 6.5 Ma。与此同时，通过野外详细勘察，前人古生物资料的系统梳理、归纳和总结并利用数学统计手段厘定了天山南麓库车坳陷早期有争议的新生代磁性地层年代，查明古地磁极性柱对比差异是造成地层年代分歧的主要原因。在上述基础上，本项目通过对库车坳陷2条地震剖面进行的平衡剖面恢复，发现新生代以来库车坳陷的地壳缩短在空间上（由西向东）具有逐渐减弱的特征，时间上具有逐渐加强的特点并在2.6 Ma以来达到顶峰。结合生长地层、沉积通量和沉积速率等构造指标，共同捕获了研究区新生代以来经历了36 Ma，13 Ma以及 6.5 Ma三期重大构造变形隆升事件，特别是6.5 Ma以来构造变形开始明显加速，它们可能是对南天山新生代构造隆升的同步响应。这为完善、深入理解和构建整个天山的形成演化模式提供了新的线索。