中文摘要：

为获得不受粒度分选效应影响的黄土矿物学风化指标,对甘肃西峰和山西吉县黄土-古土壤典型样品分离成9个粒级后进行了X射线衍射测试,分析了不同粒级中钾长石/斜长石比值（K/P比值）的变化规律。研究结果表明,黄土-古土壤中K/P比值受粒度分选效应的影响,细粒级（〈1μm,1~2μm）的K/P比值显著高于粗粒级（〉2μm）;黄土在源区的沉积旋回过程中和沉积区的成壤过程中斜长石都经历了一定程度的化学风化作用,呈现出大陆风化早期阶段特征,并且这种风化作用主要发生在细粒级中,因此,黄土和古土壤（2 um K/P比值能够有效地排除粒度分选效应的影响,直接指示黄土沉积在源区和沉积区风化作用。

英文摘要：

To develop a mineral index of weathering without effect of grain-xize sorting,loess and paleosol samples were separated into nine different particle fractions and the K-feldspars/plagioclase ratio（K/P ratio） was determined based on X-ray diffraction data.We also examine the spatial variations of the 2 μm K/P ratio from Huanxian to Weinan along the Loess Plateau.Results show that the K/P ratio of loess and paleosol is higher in the 2 μm fractions than in the 2 μm fractions,implying that plagioclase in loess deposits has experienced the incipient stage of chemical weathering in dust sorece regions and on the Loess Plateau.However,the spatial distributions of the 2 μm K/P ratio show that higher values in soil units than in loess Plateau transect.These are in good agreement with the temporal-spatial variations in the East Asia summer monsoon intensity identified by other monsoon proxies and soil development observations.The 2 μm K/P ratios thus attests to a good proxy indicator of the chemical weathering intensity of loess in the Loess Plateau.