宇宙成因核素~(10)Be揭示的北祁连山侵蚀速率特征

山脉侵蚀速率的大小和时空分布信息是研究山脉构造—气候相互作用和地貌演化的关键切入点,其大小是受气候还是构造控制争论已久。宇宙成因核素10Be方法为从千年至万年尺度上定量研究流域平均侵蚀速率提供了一种先进和快捷的技术手段,为揭示侵蚀速率与现代气候和构造地貌因子的关系并进行相关分析提供了基础。利用该方法对北祁连山近现代侵蚀速率进行了研究。所采集的9个流域现代河沙样品,结合前人数据进行共同分析,结果显示该区侵蚀速率的变化范围为18.7~833 mm/ka,北祁连山中段的侵蚀速率约为323 mm/ka,该区侵蚀速率与降雨量没有明显的对应关系,但与流域平均坡度呈现很好的非线性关系,揭示坡度是该区侵蚀速率的最主要控制因素。通过对比北祁连山地表平均侵蚀速率和该区域的断层垂直滑动速率发现整体上该区域地表侵蚀速率要低于祁连山北缘断层的垂直滑动速率,反映了北祁连山正处于地形抬升和生长的过程之中。

Erosion Rates of Northern Qilian Mountains Revealed by Cosmogenic 10Be

Knowledge of temporal and spatial distribution of erosion is the key to understanding the climate-tectonic interaction and topographical evolution of mountain belts and to making clear the long debate whether erosion is controlled by tectonics or climate. The newly developed cosmogenic nuclides method provides us with an advanced and convenient tool to measure millennium basin-wide erosion rate, allowing us to analyze its relationship with modern climatic, geomorphic and tectonic factors. Hence, we adopted the ¹⁰Be method to investigate the basin-wide millennium erosion rates of Northern Qilian Mountains and aimed to find the controlling factors of erosion rates of this area. We collected and analyzed 9 samples from Heihe River and the front of the Northern Qilian Mountains. Our results, together with published ¹⁰Be derived erosion rates in this area, showed that the erosion rates of the basins we studied ranged from 18.7 mm/ka to 833 mm/ka, and that the weighted average erosion rates of the middle section of the Northern Qilian Mountains was about 323 mm/ka. Spatial distribution of erosion rates and correlation analysis reveal that the basin-wide erosion rate was nonlinearly correlated to the basin average slope, while no apparent correlation between erosion rate and precipitation was found. Altogether, it indicated that the slope or terrain steepness was the major controlling factor on erosion rate of the Northern Qilian Mountains area. By comparing the basin-wide average erosion rates and the vertical slip rates of faults of the Northern Qilian Mountains, our research also revealed that the surface erosion rates generally agreed with vertical slip rates of the Northern Qilian Mountains faults, implying that the Northern Qilian Mountains area was experiencing topographical uplift and outgrowth.