青藏高原东北缘黄土粒度组成及物质来源分析

Grain-size distribution and material source analysis of loess on the nort heastern margin of the Qinghai-Tibet Plateau

对青藏高原东北缘的民和黄土进行粒度分析发现,民和黄土粒度组成与兰州、洛川和西安等地差别较大,其黄土粒度明显大于上述地区。传统地把民和黄土划分为黄土带的南部过于简单化,它忽略了因青藏高原隆升而激发产生的高原物源区作用,应将民和黄土归属于黄土与砂黄土的过渡带。青藏高原因冰川反复消融和磨蚀产生的砂尘为民和黄土提供了可观的粗物质补给。事实表明,青藏高原第四纪冰川-冰融作用所产生的大量砂粉尘,不仅是高原腹地黄土区的主要物源,也是青藏高原边缘黄土的主要物源之一。

Grain-size analysis of the Minhe loess on the northern margin of the Qinghai-Tibet Plateau in-dicates that the grain-size distribution of t he Minhe loess is obviously different from that in other areas such as Lanzhou and Luochuan and Xi'an.Its grain size is notably much higher.It seems too sim ple to as-sign the Minhe loess to the southern part of the loess belt traditio nally because of ignorance of the effect of the plateau source area induced b y the uplift of the Qinghai-Tibet Plateau.It is advisable to assign the Minhe loess to a transition zone between loess and sandy loess.The sandy dust produc ed as a result of re-peated glacial ablation and abrasion of the plateau has supplied a substantial amount of coarse material for the Minhe loess.The vol uminous dust produced by the Quaternary glaciation and melting of glaciers on the Qinghai-Tibet Plateau is not only the principal material source for the l oess area in the interior of the plateau but alsoone of the principal materi al sources for the loess on the margins of the plateau.