Transformation of displacement between strike-slip and crustal shortening in the northern margin of the Tibetan Plateau: Evidence from decadal GPS measurements and late Quaternary slip rates on faults

摘要

Studies of Late Quaternary geological slip-rates and the GPS decadal slip-rates along the major strike-slip faults in the northern margin of the Tibetan Plateau show that slip-rates remain relatively constant along the middle sections of each fault and decrease rapidly toward the ends. Our recent studies suggest that the slip rates are low (<. 10. mm/yr) along the major strike-slip faults, i.e., Altyn-Tagh fault and Qilian-Haiyuan fault. West of 95°E, the slip rate on the Altyn-Tagh fault has been determined to be 8-12. mm/yr, and gradually decreases from 95°E eastward to about 1-2. mm/yr at the easternmost segment of the fault. The slip-rate of Qilian-Haiyuan fault is about 1-2. mm/yr near the Halahu Lake, near the western tip of the fault, then increases to a relatively constant value of 4-5. mm/yr in the Qilian area (101°E and eastward). Eastward, the fault merges into the NS trending Liupan Shan fault zone east of Haiyuan, and the slip rate drops to 1-3. mm/yr, or even lower. Our present observations on the variation and distribution of slip rates along the major strike slip faults indicate that slip on the Altyn-Tagh fault is mainly dissipated through internal deformation, by thrust faulting within the Qilian Shan and shortening within the adjacent Cenozoic basins. Left-lateral strike-slip on the Qilian-Haiyuan fault might be transformed into shortening and growth of the Liupan Shan to the east, and may also contribute partially to the deformation in the western Qilian Shan. In conclusion, the distribution of slip rates from both late Quaternary geological records and the current GPS observations suggest a decrease in slip rate, a redistribution of strain, and the transformation of displacement along the major strike slip faults into crustal shortening, basin formation and mountain uplift that characterize present-day deformation of the northern margin of the Tibetan Plateau.