基于ESR年代的川西高原河流下切速率

Quaternary fluvial incision rates of the Western Sichuan Plateau inferred from ESR chronology

根据野外地质地貌调查,查明了川西高原大渡河泸定段、鲜水河炉霍段的阶地序列,并应用ESR法测定了河流阶地的形成年代.结果表明:这些河流阶地序列均形成于更新世以来,由阶地拔河高程及形成年代确定的大渡河泸定段、鲜水河炉霍段更新世以来的平均下切速率分别为0.38,0.39 mm/a,与杂谷脑河理县段下切速率0.39 mm/a一致,也与(U-Th)/He低温热年代学反映的下切速率一致,这也反映出川西高原更新世以来构造抬升的整体性.这些河流下切速率比由磷灰石裂变径迹数据得出的鲜水河断裂与龙门山断裂所夹的三角区域的隆升速率(>2.6±0.7 mm/a)要小得多.

Based on field observation, the fluvial terrace sequences of the Xianshui River at Luhuo, and the Dadu River at Luding were identified and dated by ESR method. The results show that all the terraces were developed during Pleistocene. The average incision rates of the Xianshui River and Dadu River were 0.38 and 0.39 mm/a, respectively. The incision rates calculated by the height of river terraces and their formation age were coincident with the exhumation rates inferred from low-temperature （U-Th）/He thermochronology. The consistent incision rates of the different rivers had recorded the coherently phased rise of the plateau during Quaternary. The river incision rates were lower than the uplift rates of the triangle area between the Xianshui River fault and the Longmenshan fault（〉2.6±0.7 mm/a） inferred from the apatite fission track （AFT） dating.