Evaluating the Detrital Record of Continental Collision in the Songpan-Ganzi Complex, Central China, the World's Largest Pre-Cenozoic Turbidite System

评估中国中部松潘-甘孜杂岩（世界上最大的前新生代浊积岩系统）的大陆碰撞碎屑记录

• 批准号: 0408752
• 负责人: Stephan Graham
• 金额: $ 28.43万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-07-01 至 2007-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0408752&HistoricalAwards=false
• 关键词: Evaluating; Detrital; Record; Continental; Collision

The Songpan-Ganzi region, an area the size of Kansas on the NE corner of the Tibet Plateau, is underlain by a vast expanse of Triassic-age deep-marine sedimentary sediments (turbidites). The Songpan-Ganzi Complex (SGC) is the world's largest ancient turbidite system, comparable in volume to the largest modern sedimentary accumulation, the Bengal submarine fan, yet the sources of these sediment are very poorly known. Continental blocks and volcanic arc systems fringing the SGC ocean basin could have provided considerable sediment to the SGC. Alternatively, a likely source for the sediments is the nearby suture belt between the North China and South China continental blocks, which collided during the Triassic. With collision-driven uplift, this suture belt rapidly eroded to great depths in the monsoonal climate of Triassic-Jurassic east Asia, removing a volume of crust comparable to the sediment volume in the SGC. By analogy, the occurrence of the SGC turbidite sequence structurally wedged into a coeval suture between two continental blocks is reminiscent of the temporal and geometric elements of the modern Himalayan collision system, including the ultimate repositories for Himalayan detritus, the Bengal and Indus submarine fans. However, whereas the Himalayan system will continue to evolve far into the future, the long extinct North China/South China/Songpan-Ganzi system contains a full record of continental collision. This study is identifying the sources of sediment for the SGC through a program of analytical studies of new samples and extensive pre-existent collections (600 kg, 400 samples) housed at Stanford University, complemented by field investigation of sediment transport directions. The study includes conventional sandstone petrographic analyses, as well as sophisticated analytical approaches such as use of the Stanford-USGS Sensitive High Resolution Ion Microprobe (in co-operation with J.L. Wooden, USGS) and Stanford's Raman spectroscopy facility to identify minerals (e.g., zircon with microdiamond or coesite inclusions) indicative of ultrahigh-pressure deep-crustal sources, currently the focus of major research efforts in the North China/South China suture zone. If suture-derived sediment can be identified in these sediments, then it may be possible to track the record of erosion of the North China/South China suture belt in much the same way that modern Bengal and Indus fan sediments archive a record of erosion of the Himalayan collision system. Thus, comparison of data from the SGC with the Himalayan system will yield better understanding of the long-term evolution of collisional systems and their sedimentary records.

松潘-甘孜地区位于青藏高原东北角，面积相当于堪萨斯州，其下分布着一大片三叠纪深海沉积（浊积岩）。松潘-甘孜杂岩（SGC）是世界上最大的古浊积岩系，其体积可与现代最大的沉积堆积孟加拉海底扇相媲美，但其沉积物来源却知之甚少。大陆块和火山弧系统边缘的SGC海洋盆地可能提供了大量的沉积物的SGC。另一种可能的沉积物来源是华北和华南大陆块之间的缝合带，它们在三叠纪碰撞。随着碰撞驱动的隆起，这条缝合带在三叠纪-侏罗纪东亚的季风气候中迅速侵蚀到很深的地方，去除了与SGC沉积物体积相当的地壳体积。通过类比，SGC浊积岩序列的发生在结构上楔入两个大陆块之间的同时代缝合线，让人想起现代喜马拉雅碰撞系统的时间和几何元素，包括喜马拉雅碎屑的最终储存库，孟加拉和印度的海底扇。然而，尽管喜马拉雅体系将继续演化到遥远的未来，长期灭绝的华北/华南/松潘-甘孜体系包含了完整的大陆碰撞记录。本研究通过对斯坦福大学的新样品和大量先前存在的样品（600公斤，400个样品）进行分析研究，并辅以对沉积物运移方向的实地调查，确定SGC的沉积物来源。该研究包括传统的砂岩岩相分析，以及复杂的分析方法，如使用斯坦福-USGS敏感高分辨率离子微探针（与J.L. Wooden，USGS）和斯坦福大学的拉曼光谱设施来识别矿物（例如，锆石与微金刚石或柯石英包裹体）指示超高压深地壳源，目前主要研究工作的重点在华北/华南缝合带。如果在这些沉积物中可以识别出缝合线衍生的沉积物，那么就有可能追踪华北/华南缝合带的侵蚀记录，就像现代孟加拉和印度扇沉积物记录喜马拉雅碰撞系统的侵蚀记录一样。因此，将SGC与喜马拉雅体系的数据进行比较，将更好地了解碰撞体系及其沉积记录的长期演化。