ABSTRACT Glaciers in central Asia that developed under a range of climatic conditions from arid to humid provide an excellent opportunity to test glacial responses to changes in climate. To do this, we mapped and dated glacial deposits at 11 sites spread over five mountain ranges in central Asia: the Altai, Tian Shan, Altyn Tagh, Qilian Shan, and Kunlun. The glacial chronologies for these sites were determined from new 10 Be and 26 Al exposure ages for the mapped moraines, in addition to 10 Be ages available in the literature. Paleo–equilibrium-line altitudes were estimated for past glacier extents from the dated moraines. The equilibrium-line altitudes (ELAs) were also estimated for existing glaciers to characterize the spatial pattern in modern climate across the study region. Differences between the modern and paleo-ELAs (∆ELAs) were used to explore the climatic reasons for variations in the glacier sensitivities and responses to past changes in climate. The results show that the glaciers in more humid regions advanced to their maximum during marine oxygen-isotope stage (MIS) 3–2 with ΔELAs of ~1100–600 m. However, glaciers in the arid interior of central Asia, in the rain shadows of the Karakorum and Pamir ranges and in the Gobi Desert ranges, reached their maximum between MIS 6 and 4, and glacier extents during the subsequent colder/drier MIS 3–2 were significantly smaller or did not extend beyond their cirques. Comparisons of our results and the sensitivity analysis of modern glaciers suggest that depression of air temperature was the primary driver of glacier advances in central Asia but that precipitation played a major role in shaping the spatial and temporal heterogeneity of glacier advances. Precipitation was especially important in hyperarid conditions. Therefore, inferences about paleoclimate parameters from past glacial extents must be made after careful consideration of the climatic setting in which the glaciers are found, as well as their sensitivity to climatic factors.

Abstract Following the c. 50 Ma India–Kohistan arc–Asia collision, crustal thickening uplifted the Himalaya (Indian Plate), and the Karakoram, Pamir and Tibetan Plateau (Asian Plate). Whereas surface geology of Tibet shows limited Cenozoic metamorphism and deformation, and only localized crustal melting, the Karakoram–Pamir show regional sillimanite- and kyanite-grade metamorphism, and crustal melting resulting in major granitic intrusions (Baltoro granites). U/Th–Pb dating shows that metamorphism along the Hunza Karakoram peaked at c. 83–62 and 44 Ma with intrusion of the Hunza dykes at 52–50 Ma and 35 ± 1.0 Ma, and along the Baltoro Karakoram peaked at c. 28–22 Ma, but continued until 5.4–3.5 Ma (Dassu dome). Widespread crustal melting along the Baltoro Batholith spanned 26.4–13 Ma. A series of thrust sheets and gneiss domes (metamorphic core complexes) record crustal thickening and regional metamorphism in the central and south Pamir from 37 to 20 Ma. At 20 Ma, break-off of the Indian slab caused large-scale exhumation of amphibolite-facies crust from depths of 30–55 km, and caused crustal thickening to jump to the fold-and-thrust belt at the northern edge of the Pamir. Crustal thickening, high-grade metamorphism and melting are certainly continuing at depth today in the India–Asia collision zone.

Abstract Group velocities for a period range of 6–60 s for the fundamental mode of the Rayleigh wave passing across the Himalaya–Karakoram–Tibet orogen are used to delineate the structure of the upper lithosphere using the data from 35 broadband seismic stations. 2D tomography velocity maps of group velocities were obtained at grids of 1° separation. Redefined local dispersion curves are inverted non-linearly to obtain 1D velocity models and to construct a 3D image of the S-wave structure down to a depth of 90 km. The Moho discontinuity is correlated with c. 4.0 km s −1 S-wave velocity. The results depict a NE-dipping trend of the Moho depth from c. 40 km beneath the frontal part of the Himalaya to up to c. 70–80 km beneath the collision zone before shallowing substantially to c. 40 km beneath the Tarim Basin. The study also reveals thick deposits of sediments in the Indo-Gangetic plains and the Tarim Basin. A broad low-velocity zone at mid-crustal depth in the western Tibetan Plateau, the Karakoram region and the surface-collision part of the India–Eurasia tectonic plates is interpreted as the effect of partial melting and/or the presence of aqueous fluid. The high velocities in the southern deeper part indicate that the lower crust and uppermost mantle of the Indian Plate are dense and cold.