Uniform postglacial slip-rate along the central 600km of the Kunlun Fault (Tibet), from <SUP>26</SUP> Al, <SUP>10</SUP> Be, and <SUP>14</SUP> C dating of riser offsets, and climatic origin of the regional morphology

International audienceLate Pleistocene-Holocene sinistral slip-rates on several segments of the Kunlun Fault in northeastern Tibet have been determined. These determinations are based on the measured displacement of alluvial surfaces whose surface ages were determined by cosmogenic 26 Al and 10 Be dating of quartz pebbles, and by 14 C dating of charcoal. In the west, at three sites along the Xidatan-Dongdatan segment of the fault, near 94°E, terrace riser offsets ranging from 24 to 110m, with cosmogenic ages ranging from ~1800 to ~8200yr, yield a mean left-lateral slip-rate of 11.7+/-1.5mmyr-1 . Field observations indicate minimum offsets of 9-12m this offset, when combined with the long-term slip-rate, indicates that great earthquakes (M ~8) rupture this segment of the fault with a recurrence interval of 800-1000yr. At two sites along the Dongxi-Anyemaqin segment of the fault, near 99°E, terrace riser offsets ranging from 57 to 400 m with 14 C ages ranging from 5400 to 37000yr BP yield a minimum slip-rate of ~10mmyr-1 . At one site, the 1937 January 7, M =7.5 and the penultimate earthquakes produced 4 m of left-slip and 0.4 m of reverse-slip. The maximum recurrence interval of earthquakes with such characteristic slip is thus ~400yr. Farther east, near 100.5°E, along the Maqen segment of the fault, the 180moffset of a lateral moraine, emplaced between the last glacial maximum (20ka) and 11100yr BP, yields a mean slip-rate of 12.5+/-2.5mmyr-1 . The slip-rates are constant, within uncertainty, throughout the 600km of the Kunlun Fault that we studied. The average slip-rate is 11.5+/-2.0mmyr-1 . Extrapolating this rate to the reminder of the fault, we conclude that most (80 per cent) of the 300 morphological offsets measured in the field or on SPOT satellite images post-date the Last Glacial Maximum. Most of the terraces we studied were deposited during the humid period of the Early Holocene Optimum (9-5ka) the formation of younger terraces reflects Late Holocene climate change