MODERN AND CENOZOIC EROSION RECORDS OF NORTHWEST TIBET AND PAMIR

Constraining erosion in the western Tarim Basin is critical to reconstructing the uplift of NW Tibet and determining the origins of the Taklimakan Desert. Sediment provenance of the desert and three major rivers draining this region is characterized using bulk sediment major element geochemistry, Nd and Sr isotope geochemistry, with detrital apatite fission track (AFT) and U-Pb zircon ages. The Hotan River drains the North Kunlun Block and is characterized by zircon populations at 160–230 Ma and 370–520 Ma. The Yarkand River shares these grain populations but also contains a very prominent population at 40–160 Ma commonly recognized in Karakoram basement, which suggests a higher sediment flux from these ranges. A stronger flux from the Karakorum indicates control on erosion by topographic steepness and precipitation mediated through glaciation. The zircon data confirm earlier studies indicating that Taklimakan Desert sediments are derived from both the Kunlun and Pamir Mountains. AFT ages are younger in the Hotan River than in the Kashgar River, which drains the Pamir, and both rivers yield ages younger than sourced from the Transhimalaya and adjacent parts of the western Tibetan Plateau. Comparison of modern river data with U-Pb zircon ages from Cenozoic foreland sedimentary rocks argues that the modern Yarkand River drainage is geologically young because that no sediment similar to the modern Yarkand River is recognized in the ancient record. Data here indicate uplift of the North Kunlun had started by ~17 Ma, somewhat after uplift of the Pamir and Songpan Garze of NW Tibet, dated before 24 Ma. Sediment sourced from the Kunlun Mountains first appears in the foreland basin between 14 and 11 Ma. AFT ages further constrain that North Kunlun exhumation accelerated before 3.7 Ma, likely linked to faster rock uplift rather than climate change.