Glacial Landform Chronology and Environment Reconstruction of Peiku Gangri,Himalayas

Xixabangma-Qomolangma(Xixabangma-Everest) region is an intensively glaciation centre in monsoonal Himalayas,and relic glacial landforms are widely distributed in the glacial valley.Relatively well preserved geomorphic and sedimentary sequences make the region to be a key region for reconstructing Quaternary glaciations and environmental evolution in the Tibetan Plateau.Based on field geomorphologic surveying and 10Be terrestrial cosmogenic nuclide(TCN) exposure dating,Quaternary glacial events in the Laqu valley on the northern slopes of Mount Xixabangma are examined;the equilibrium line altitude(ELA) and their climatic implication are discussed.The glacier expanded down to pediment and became pediment glacier in Laqu Valley during the Last Glacial.The glacierized area was 99.9 km2 and the equilibrium line altitude was 5 620 m for Laqu I;the glacierized area was 97.6 km2 and the equilibrium line altitude was 5 600 m for Laqu II.Compared with the ELA at present,the equilibrium line altitude of Laqu I and Laqu II declined 380 m and 400 m,respectively.There were several glacial advances in the Laqu Valley during the Last Glacial,10Be exposure age is 42.1～22.3 ka for Laqu I,and 10Be exposure age is 18.6～14.8 ka for Laqu II.Based on geomorphologic methods,the climate at ELA of Laqu I and Laqu II were reconstructed,and the temperature was-10.7 ℃ and precipitation was 251～461 mm for Laqu I;the temperature was-10.6 ℃ and precipitation was 261～480 mm for Laqu II;the temperatures at the ELA are considerably close to that at present,but the precipitations are much less than that at present,showing the glacier belonged to sub-continental type during the Last Glacial with weak Indian Monsoon.