东北印度洋尼科巴扇沉积记录及其对喜马拉雅东段水系演化和隆升剥露历史的意义

喜马拉雅东构造结是地球上岩石隆升和剥露速率最快的地区之一，其快速隆升剥露被认为是由布拉马普特拉河对雅鲁藏布江的袭夺触发的。然而目前无论是雅鲁藏布江-布拉马普特拉河的贯通时间，还是东构造结快速隆升剥露的开始时间都存在争议。尼科巴扇作为雅鲁藏布江-布拉马普特拉河的最终沉积区，是了解喜马拉雅东段水系演化和隆升剥露历史的重要窗口。IODP 362航次在尼科巴扇成功钻取了早中新世以来的沉积物。本项目拟在航次工作基础上，通过微体化石加密分析提高生物地层框架的分辨率，利用地球化学以及碎屑锆石U-Pb年龄和Hf同位素分析示踪沉积物源区，利用碎屑锆石裂变径迹定年反演源区岩体的隆升剥露历史。综合以上工作，我们可以根据冈底斯弧物质的出现来约束雅鲁藏布江-布拉马普特拉河的贯通时间；结合沉积速率、源区属性和源区岩体隆升剥露历史限定东构造结快速隆升剥露的开始时间；并进一步探讨东构造结隆升剥露与河流袭夺贯通的成因联系。

The eastern Himalayan syntaxis is one of the areas suffering most rapid exhumation on Earth. The rapid exhumation is regarded as the result of capture of the Yarlung Tsangpo by the Brahmaputra River. However, both the timing of the integration of the Yarlung Tsangpo-Brahmaputra River and initiation of the rapid exhumation of the eastern syntaxis are debated. As the ultimate sedimentary trap of the Yarlung Tsangpo-Brahmaputra River, the Nicobar Fan becomes a window to look into the drainage evolution and exhumation history of the eastern Himalaya. International Ocean Discovery Program (IODP) Expedition 362 drilled the Nicobar Fan for the first time, recovering fan sediments dated back to the Early Miocene. We plan to conduct higher density analysis on microfossils to improve the resolution of the biostratigraphic framework base on the onboard and post-cruise study. Bulk sediment geochemistry and detrital zircon U-Pb chronology and Hf isotope will be investigated to trace the provenance. Detrital zircon fission track dating will be conducted to interpret the exhumation history of the bedrock in source areas. Particularly, we aim to constrain the timing of the integration of the Yarlung Tsangpo-Brahmaputra River by detecting the first appearance of the Gangdese arc material in the Nicobar Fan sediments, and to constrain the timing of the rapid exhumation of the eastern Himalayan syntaxis by integrating the variations of sedimentary rate and provenance and the exhumation history of the bedrock in source areas. Therefore, we will further understand the coupling between the rapid exhumation of the eastern Himalayan syntaxis and the river capture event.