CLIMATIC IMPLICATION AND GRAINS SIZE COMPOSITION FROM MINHE LOESS IN QINGHAI PROVINCE

The sample collecting and grading analysis of Minhe loess in Qinghai Province,located in the northeast fringe of Qinghai-Tibet Plateau,indicates that the grains size of Minhe loess is coarser than that of other regions such as Lanzhou.The 30 μm and 50 μm coarse grains respectively denote intensity change of winter monsoon and the role of loess source area stimulated by the uplift of Qinghai-Tibet Plateau.The surface of plateau supplies abundant coarse matters for Minhe loess with cold weathering material and glacial till.It is the uplift of plateau and other regional tectonic movement that leads to the diversification of the source area of loess.This mainly explains the difference of grain sizes in the loess that plateau uplifting and intensity change of winter monsoon induced by the uplift of plateau,and regional tectonic movement and the difference in configuration of topography,of the interaction between plateau monsoon and ambient flow,as well as the difference in source area of loess and the variation in the range of the source area.