Polygon-Veins along the Qinghai-Xizang Highway
Liang Fengxian and Cheng Guodong ( Lanzhou Institute of Glaciology and Geocryology, Academia Sinica )
Based on the principle scheme of polygon-veins suggested by Roman-ovskiy, the polygon-veins along the Qinghai-Xizang Highway have been investigated in detail, some new points of view obtained, and their classification according to activity and size attempted. Small-sized polygon-veins, both active and fossil, belong to orignal sand vein of high temperature type, the active middle-sized polygon-veins belong to original sand vein of transitional type, while the fossil middle-sized polygon-veins though belong to transitional type also, but according to different humidity on-ground surface are separated into original sand vein, original soil vein, residual ice-soil vein or sand-ice vein respectively, differing from the ice wedge cast regarded before. Most of the fossil large-sized polygon-veins are of transitional type, only a few of them may be ice wedge casts. From statistical analyses,the relationships between distributive elevation and latitude or longitude have also been found. Further analysis indicates that both the large-sized and middle-sized fossil polygon-veins were formed by the end of the Late pleistocene period. Based on the temperature for the formation of polygon-veins suggested by Romanovskiy with our revision for mountain uplift,it is estimated that the mean annual air temperature in Late Glaciation might be 6-8℃ lower than that at present, coincident with estimations through other methods.