渐新-中新世珠江流域变迁和珠江口盆地碎屑沉积物低温热年代学响应

Based on the theory of source-to-sink, this proposal intends to do low-temperature thermochronologic study on the Oligocene and Miocene sediment in the Pearl River Mouth Basin.We will build a basin-wide framework for filling sequences and stratigraphic sequences for these sediments. In addition, we will also quantify its sedimentary fills and the rates of accumulation by dividing the sediment volume by the duration of each depositional episode. The detrital (U-Th)/He and fission track (FT) dating will be employed in our study. Together with the result from the detrital zircon U-Pb dating, we will simulate the erosion rates for the Pearl River. We will decipher the erosion rates and estimate the eroded volume by low-temperature thermochronologic dating on the rocks in the catchment area. According to the mass balance theory, we will compare the erosion rate in the source areas and subsidence in the sedimentary basin to constrain the style and time for the reorganization of the Pearl River, which will get critical information about the coeval relationship between the South China block, the Pearl River and the basin subsidence. The Pearl River catchment’s evolution is closely relationship with the uplift the Tibet, relief inversion of the East Asia and oceanic crust formation in the South China Sea, which must be a key scientific question for studying source-to-sink in the East Asia. This study will enhance our understanding on this question after our evidence from onshore-offshore study, which will be helpful to the petroleum exploration in the Pearl River Mouth Basin.

本课题基于“源-汇系统”的研究思路，选择珠江口盆地内与珠江流域演化的关键时期—渐新世-中新世同时代的沉积物开展系统的低温热年代学研究。建立盆地高精度层序地层格架，定量计算盆地渐新世-中新世不同时期的沉积物通量；开展珠江口盆地碎屑岩(U-Th)/He年龄和裂变径迹热年代学、碎屑锆石U-Pb年龄等测试分析和数值模拟计算；根据物质平衡的原理，确定珠江流域关键构造部位的剥蚀速度和珠江口盆地沉降过程的定量对比关系，明确限定珠江流域最终重组和变迁演变的时间，进而揭示华南陆缘构造转换、珠江流域水系演化和盆地沉降之间关系的关键信息。珠江水系的变迁受控于新生代青藏高原的崛起、东亚地形的倒转和南海洋盆的形成的宏观格局下，是东亚“源-汇系统”领域重要的科学问题之一，本研究将有助于为该问题的解决提供来自“海陆结合”方面的综合证据，并对珠江口盆地的油气勘探有实际的应用价值。

陆缘盆地堆积了来自大陆丰富的沉积物，保存了记录大陆构造、沉积、气候和河流演化等地球表层动力学信息。本次研究以南海北部珠江口盆地为研究对象，建立由海向陆统一的时空对比框架，重点刻画了珠江口盆地深水/超深水区地壳尺度上的拆离断层的三维结构及其所控制的沉积充填序列；确定了T70界面（~33Ma）和T40界面（~16Ma）限定的地层为裂解层序，厘定该层序是南海北部陆缘岩石圈破裂过程的沉积记录；根据构造地层分析和年代学研究发现岩石圈地壳的强烈伸展作用改变了南海西北部源汇系统；对珠江口盆地深水区开展了系统的碎屑锆石U-Pb定年研究，确定了南海北部大型水系对深水区的影响至少应从中新世开始；基于高精度数字高程模型分析和宇宙成因核素10Be定年法确定珠江口盆地西部海南岛现今剥蚀速率较低；同时，开展了珠江口盆地关键钻井岩石样品的采集，开展了碎屑岩低温热年代学研究，识别记录的陆缘大型水系的演化。基于以上认识，建立了华南陆缘隆升-珠江口盆地沉降-陆缘大型水系演化的大陆边缘演化模式，研究成果丰富了大陆边缘动力学。