西藏羌塘地块白垩纪晚期构造变形与高原早期隆升关系研究

How and when the Tibetan plateau developed has long been a puzzling question with implications for the global climate change and models of continental deformation. The deformation and its relationship to the surface uplift process of the plateau is an essential problem to the geologic evolution of the Tibetan plateau. However, the relevance is still debated. Some researchers suggest that the central Tibet was raised to the present elevation during Late Cretaceous, and attribute the geodynamics to the Lhasa-Qiangtang collision and subsequently underthrusting of the Lhasa block beneath the Qiangtang block. Others argue that no evidence exists in favor of the existence of a proto-Tibetan plateau prior to the Cenozoic. A major problem in tectonics is how crustal shortening contributed to the uplift of the plateau in central Tibet during Late Cretaceous. To better constrain the uplift history of the central Tibetan, the deformation and uplift of the Qiangtang block is crucial. However, it is poorly known. Due to the above problems, we propound this proposal. The aim of this proposal is to make clear the deformation, crustal shorten and uplift of the Qiangtang during Late Cretaceous. Firstly, we will confirm the deformation and crustal shortening of the Qiangtang block during Late Cretaceous by means of structure analyses, geochronology and balanced cross section. Secondly, we will carry out thermochronology, basin analyses to decipher the uplifting, and denudation of the Qiantang block prior to the Cenozoic. Finally, based of the above researches and analogy with the Lhasa block, we will reconstruction the geological evolution and uplifting history of the central Tibet during Late Cretaceous. We believe that our researches will provide robust evidences and new insight into development of the Tibetan plateau.

青藏高原隆升过程和机制是国际地学界研究的前沿领域，而高原复杂的构造变形过程及其与高原隆升的时空关系一直是该领域研究的核心内容之一。由拉萨地块构造变形研究提出的青藏高原中部在白垩纪晚期因拉萨-羌塘碰撞导致早期隆升是该区长期存在争议的问题，本申请针对国际上目前对上述认识存在的问题与争议，以同类研究程度较低的羌塘地块为研究对象，以构造变形分析、构造年代学和平衡剖面等技术为主要手段，在查明白垩纪晚期构造变形特征及其与地壳缩短增厚关系的基础上，结合构造热年代学、沉积盆地分析、以及区域对比等研究，确定羌塘地块白垩纪晚期构造变形特征与高原早期隆升的关系，进而探索青藏高原中部白垩纪隆升过程及其动力学机制。研究成果不仅对认识青藏高原中部早期隆升历史和机制具有重要的意义，而且对全面认识整个高原隆过程和时空演变规律具有重要的科学意义。

青藏高原隆升过程和机制是国际地球科学研究的前沿领域和热点问题，而高原复杂的变形过程及其与高原隆升的时空关系一直是该领域研究的核心内容。本项目以青藏高原中部羌塘地块白垩纪晚期以来构造变形和高原隆升关系研究为重点，分析地块白垩纪以来变形特征、性质及其与地壳缩短增厚、地表隆升的关系，探讨高原中部隆升过程及其动力学机制，为全面认识整个高原隆过程和时空演变规律提供依据。项目主要研究内容包括：1）羌塘地块白垩纪晚期以来构造变形与地壳缩短作用；2）白垩纪晚期以来隆升历史；3）白垩纪晚期以来构造演化与高原隆升的关系。通过研究取得了如下主要认识：1）通过精细的构造研究，查明地块白垩纪以来变形特征、缩短量及其与地壳增厚的关系，提出地块在~100Ma和50-38 Ma发生2期强烈变形，两期变形分别代表了拉萨-羌塘和印度-欧亚碰撞作用，其中第二期缩短量为42-50%，是导致青藏高原中部强烈地壳缩短与地表隆升的主要原因。2）羌塘地块构造热年代学研究结果表明，地块主要经历了120–100 Ma和55-38 Ma两期快速剥露，两期剥露与该地区的地壳变形时间一致，构造变形和地壳增厚是导致该地区隆升和剥露的主要原因。3）通过对羌塘盆地典型地层剖面研究和沉降史恢复，恢复了不同单元沉降曲线，提出青藏高原中部最早的地壳增厚发生于150-130 Ma，即早白垩世高原中部可能开始隆升。4）对羌塘盆地晚侏罗世-白垩纪岩浆作用机制进行了研究，建立了盆地白垩纪岩浆事件序列、以及岩浆作用与班-怒洋闭合、拉萨-羌塘、印度-欧亚碰撞以及高原隆升的关系。上述认识对青藏高原中部存在的重大地质问题提出了新的认识和观点，深化了对青藏高原中部构造演化及其与高原隆升的关系认识，同时对全面认识整个高原隆升历史具有重要的科学意义。