低温热年代学重建贵德地区新生代构造地貌发育过程

The Guide region, located at the conjunction of the Qilian Shan and Western Qinling orogenic belts, is characterized by the well-preserved layered landforms and relative completed basin succession in the northeastern margin of Tibetan Plateau. The growth processes of its Cenozoic tectonogeomorphology are mainly governed by, and thus record the details of, the far-field effects of India-Asia collision and Tibetan uplift extended to the eastward of the Western Qinling syntaxis. Therefore, to accurately detect and decipher these documents (the in situ layered landforms and basin succession) can not only provide a key constraint to further understanding the formation and evolution of the Tibetan Plateau, but also increase the rare evidence till now. The low temperature thermochronology, the most fashions are the zircon and apatite fission-track and (U-Th)/He thermochronology (ZFT, AFT, ZHe and AHe), is the sensitive and precise tool for deciphering them, favored in this study. Because, their partial annealing zones rang from 300℃ to 40℃, thus can trace the details of activity crustal surface processes, with the deep even reaching to a dozen kilometers. Base on the increasing knowledges of regional geology and geomorphology, as well as the isotopic chronology methods in our interrelated studies recently, we try to conduct a throughly study on these archives using the low temperature thermochronology. Mainly focus on the bedrocks of high altitude mountains in the periphery of the Guide Basin, on which low-relief and layered landscapes has developed and relicted, as well as the synorogenic deposits, such as the Cenozoic sediments, river terraces and modern Yellow River deposits in the Guide basin, a metasynthesis study is carried out by an optimizing strategy of the multiple low temperature thermochronology, thus can achieve mutual compensation of advantages among ZFT, AFT, ZHe and AHe, to yield a whole Cenozic exhumation and evolution sequence of regional tectonogeomorphology. Futhermore, Integrating with the provenance analysis of the heavy mineral, paleocurrent and clastic composition, as well as the existed information, we finally try to reconstruct the growth history of such plateau region during the Cenozoic. These results can contribute to improve our understanding of the interaction among the “tectonic - uplift - denudation/planation - climate change”, regarding the formation and evolution history of the Tibetan Plateau.

祁连山与西秦岭两重要构造带交汇处的贵德地区处于高原东北向生长的构造敏感部位，在高原东北缘的盆山体系中具典型性和代表性。然而至今该区新生代构造地貌演化方面研究匮乏。本申请拟充分利用我们前期研究的积累，重点选取构造地貌发育过程中的直接信息载体（地质地貌岩体）以及相关沉积（盆地沉积物、现代河流沉积物、阶地序列），采用磷灰石和锆石裂变径迹和（U-Th）/He热年代学这些优势互补方法的优化策略，对这些相互区别又相互联系的信号载体进行综合集成分析，结合物源区分析（重矿物、古水流、砾石成分）和前人研究成果，重建新生代贵德地区的构造地貌发育过程，探讨区域内外力作用时限和耦合关系，揭示隆起过程，为深层次理解高原构造-隆升-剥蚀/夷平-气候变化相互作用重大理论问题提供高原东北缘关键的、相对完整的构造地貌低温热年代学序列。

本项目主要在贵德盆地及其周源进行阿米岗-甘加-阿什贡-尕让-革皮匝剖面（已精确定年）、现代河流沉积物和九级阶地序列、沉积物源区地貌面（夷平面、剥蚀面）的锆石和磷灰石优选测试矿物的(U-Th)/He 年代学和裂变径迹方法的综合集成研究。同时进行了沉积物的重矿物、古水流、砾石成分统计为主的物源区分析。解译出该区自白垩纪以来共发生约7个期次的重大构造构造活动事件序列,分别发生在63-48 Ma, 36-33 Ma, 29-27 Ma, 24-22 Ma, ~13 Ma, ~10 Ma and 7-6 Ma。精确厘定了包括研究区在内的整个西秦岭及其周缘层型地貌面的分布范围和展布规律。确定该区大地貌面（夷平面）共有两个期次，分别发育于始新世中期和渐新世末-中新世初。揭示出随着新生代印度-欧亚大陆碰撞和汇聚，该区自古近纪早期即开始同步响应，并且表现为构造活跃期和构造静止期相间出现。前者表现为盆地周缘的岩体第次隆起成为盆地新的物源区，有时构造变形深达地幔岩石圈，从而吸收高原汇聚的能量。而后者表现为地表在外力作用下的均夷过程，有时该作用持续时间高达10 Ma，具备形成准平原的条件；在此状态下，区域构造应力在地表表现为沿着走滑断裂以构造旋转等方式传递，而在下地壳乃至更深层次，汇聚应力可能主要由岩体流变传导。该区在新近纪以来经历至少3个期次的快速隆升过程，该区现代构造地貌格局最终在中新世晚期-上新世奠定。围绕上述研究结果，已发表SCI论文4篇，中文核心1篇。已投SCI论文两篇，正在撰写3篇。培养博士和硕士研究生各5名，本科生5名，参加国内外学术会议19人次（两次国际学术会议8人次）。邀请国外专家交流访问5人次。这些结果不仅对准确理解青藏高原东北缘构造隆起的过程和机制至关重要，而且还能为深入理解高原构造-隆升-剥蚀/夷平-气候变化相互作用重大理论问题提供关键的构造-地貌依据。