Pleistocene Glaciations on the Northwestern Tibet

As a result of its immense size and high elevation, the Tibetan plateau plays a major role in affecting global climatic changes, and in particular the Asian monsoon system. Consequently knowledge of its glacial evolution during the Quaternary is an essential parameter. However, the chronology and extent of Quaternary glaciations on the Tibetan plateau is still in debate. Based on ice cores and other geological settings from the Tibetan plateau, it is inferred that temperatures during LGM were depressed by 6-9 ° C. Kuhle (1998) proposed an extensive ice sheet on the Tibetan plateau during LGM, whereas others believe that, because of extreme aridity, the ELA depression in the western and interior sections is less than 300m. Thus, given that a large fraction of the Tibetan plateau surface would be below the ELA during LGM times, the extent of the proposed ice sheet would presumably be limited. We determined in situ cosmogenic nuclides Be-10 and Al-26 in young volcano samples located in Ashikule basin, western Kunlun Shan. The eruption ages of the samples are 130+/-40ka, 340+/-10ka and 780+/-140ka, dated by the K-Ar method. The exposure ages of the samples are, however, 70+/-7ka, 150+/-7ka, 160+/-8ka, respectively. All samples analyzed possess lava flowing textures, which suggests no erosion since eruption. Field observations indicate no sediment nor vegetation on the samples. Thus, the age differences most likely reflect ice and snow cover on the samples. The current ELA in western Kunlun Shan is about 6000m, whereas the samples are located at an elevation of 4800m. This implies that ELA depression in the western part of the Tibetan plateau was most likely larger than 1200m during LGM. If the interior of Tibetan plateau has a similar ELA depression, a large part of Tibetan plateau surface would be above the ELA during LGM. Therefore, Pleistocene ice coverage on the Tibetan plateau may be more extensive than previously recognized. Kuhle (1998) Quaternary International 45/46,71-108.