青藏高原周缘流域尺度土壤产生方程的铀同位素破碎年龄学证据

SOIL PRODUCTION FUNCTION AT BASIN SCALE TESTED BY URANIUM COMMINUTION AGE IN TIBETAN CATCHMENTS

剥蚀速度与风化带深度的关系是理解构造和气候影响化学风化的关键。在土壤剖面尺度，经典土壤产生方程表明剥蚀速度随着土壤深度的增加呈指数级下降。但是，剥蚀速度与土壤厚度的关系在流域尺度还不明晰。细粒物质的（234U／238U）比值记录了颗粒自破碎以来经历的时间，受控于土壤厚度与物理剥蚀速度的比值，可能为研究流域尺度的土壤产生过程提供新的手段。本研究调查了青藏高原及其周边多个地貌单元河流沉积物的铀同位素破碎年龄。结果表明，流域尺度上土壤颗粒破碎年龄与剥蚀速度的关系符合经典土壤产生方程的预测。

The relationship between the erosion rate and weathering depth is of critical importance to an understanding o5 the influence of tectonic and climate on chemical weathering. At soil profile scale, the classical equation of soil production showed that the erosion rate decreased exponentially with increasing soil depth. However, the relationship between erosion rate and soil depth is not clear at basin scale. The （234U/238U） ratio of fine particles can record the time since the particle breaking, which depend on the soil depth and erosion rates, may provide a new technique to study the soil production function at basin scale. This study investigated the （234U//238U） ratio of the catchment sediments across several geomorphic units on the Tibetan Plateau and its surrounding areas, including Gobi Alluvial Fan （0.939±0.013）, the central Tibetan Plateau（0. 932±0. 022）, the upper Yellow River（0. 925±0. 001）, the catchments of Northern Qilian Mountains （0. 961±0. 004） , Golmud River basin （ 0. 973± 0. 007 ） , Minjiang River （ 1. 001± 0. 003 ） and Gongga Mountain （0. 992±0. 006）. The results show the （234U/238U） ratio of catchments on each geomorphic unit has a good positive correlation with the denudation rate. The comminution age of the fine particles decreases with the increasing denudation rate. The relationship between uranium comminution age of soil particles and erosion rates is consistent with the theoretical prediction, proving that the classical soil production function can be applied to the basin scale.