QUATERNARY GLACIATION OF TIBET AND THE BORDERING MOUNTAINS

Tibet and the bordering mountains is one of the best natural laboratories to examine the nature of landscape evolution within a glaciated continent–continent collision zone. Determining the extent and timing of Quaternary glaciation in this region is the first step in assessing the degree to which glaciers erode landscapes and may help to enhance mountain building by denudational unloading, limit relief production and fluvial incision, and upon deglaciation may lead to rapid landscape modification. New satellite remote sensing and analytical methods such as terrestrial cosmogenic nuclide and optically stimulate luminescence dating has increased the attention being paid to defining the extent and timing of Quaternary glaciation throughout the region. Much focus has been placed on the desire to examine the relative roles of the Asian summer monsoon and mid-latitude westerlies in driving glaciation for paleoclimatic/paleoenvironmental studies. These studies show significant glacier advances over the past several glacial cycles, with many valleys preserving glacial geologic evidence for at least four glacier advances during the Quaternary. Moreover, at least nine major regionally synchronous glacier advances are evident throughout the semi-arid and monsoon influenced regions over the past ~400 ka. Moreover, the higher resolution of the Holocene glacial geologic record allows ~12 regional glacier advances to be resolved, albeit somewhat restricted in extent. However, complex variations in the timing and extent of late Quaternary glaciation are apparent over relatively short distances (10–100 km). This is well illustrated at the western end of the Himalaya, where the local last glacial maximum occurred at different times with vastly different glacier extents. Within semi-arid regions, the style of glaciation has changed significantly over the last several glacial cycles, from expanded ice caps to entrenched valley glaciation. Rather than a single driver of Himalayan glaciation and its associated landscape change, the timing and extent of glaciation and the preservation of glacial evidence is likely governed by a complex combination of different factors specific to each locality, including climate and microclimate regimes, tectonic setting, topographic controls and geologic setting.