念青唐古拉山脉西段第四纪冰川作用

在念青唐古拉山脉西段南北两麓及切割山脉的各沟谷中,分布着3套更新世冰川沉积物。在本区最长的现代冰川———西布冰川的前端,也分布着3组全新世冰川沉积物。根据这些冰川沉积物的地层层序和冰川与湖泊沉积物的电子自旋共振(ESR)、U系等时线和光释光(OSL)年龄测定结果,本文将念青唐古拉山脉西段所发生的3次更新世冰川作用,分别命名为宁中冰期、爬然冰期和拉曲冰期,并与青藏高原的邻近地区进行了对比。各次冰期的冰川性质分别为大型山麓冰川、中小型山谷冰川和小型山谷冰川。全新世时期,现代冰川也有新冰期和小冰期的两次冰川前进。近期冰川则发生了明显的后退。本文还根据念青唐古拉山脉两麓冰前期、历次冰期和现代砾石层的砾石岩性及其与山脉各构造层岩性组成的对比,讨论了山脉的剥蚀与隆升问题

QUATERNARY GLACIATIONS IN THE WEST NYAIQENTANGLHA MOUNTAINS

Along the south and north feets as well as in individual valleys of the West Nyaiqentanglha Mountains, there are three sets of Pleistocene glacial deposits. The first set is distributed at the feet of Nyaiqentanglha, constituting the high piedmont moraine platforms 150～350 m higher than the valley bottoms. On their front margins, there are always simultaneous high fluvioglacial platforms. The second set is mainly distributed in glacial troughs cutting the mountains and their outlets, constructing the high lateral and terminal moraines 30～80m higher than the valley bottom. The third set is also distributed in glacial troughs, constituting the low lateral and terminal moraines 5～15m higher than the valley bottom. In front of the Xibu glacier extended over ten kilometers, the longest one in the West Nyaiqentanglha Mountains, there are also three groups of Holocene terminal moraines. Three glacitions corresponding to the three sets or groups of moraines are named in this paper the Ninzhong Glaciation (0.7～0.6MaB.P.), the Paran Glaciation (0.2～0.14 MaB.P.), and the Laqu Glaciation (0.07～0.03 MaB.P.). Their ages are determined by methods of ESR, U-series, and OSL. Glaciers due to the three Pleistocene glaciations are various: large-scale piedmont glaciers, middle- and small-scale valley glaciers and small-scale valley glaciers. The Xibu glacier advanced two times: one in the Neoglaciation and one in the Little Ice Age. In last decades, however, it retreated obviously. Finally, through compositional correlations of the preglacial, glacial and modern gravels with rocks in three structural strata of the Nyaiqentanglha Mountains, the denudation and uplift of the mountains were discussed and the history of glacial evolution was traced.