青藏高原中段活动断层运动速度及驱动机理

Slip Rates and Driving Mechanism of Active Faults in Middle Tibetan Plateau

在大比例尺活动断层勘测调查基础上,通过测定典型断层位移和活动时代,计算重要活动断层运动速度,分析青藏高原中段地壳水平运动规律。发现青藏高原中段晚更新世—全新世发育大量NW—NWW—近EW向活动断裂,其中昆仑山活动断裂、可可西里南缘活动断裂、通天河活动断裂、崩错活动断裂、念青唐古拉山东麓活动断裂和雅鲁藏布江活动断裂水平运动速度达6～10mm/a,风火山活动断裂、乌丽活动断裂和雁石坪活动断裂水平运动速度达3～4mm/a ,唐古拉山活动断裂与格仁错活动断裂水平运动速度约2mm/a。自晚更新世以来,青藏高原中段存在显著的地壳东向运动,相对于柴达木地块的地壳东向运动速度自南北两侧向中部逐步增大,至唐古拉山地区达最大值约4 0mm/a。青藏高原中段断裂活动、地壳运动与近SN向构造挤压及地壳内部东向水平剪切存在动力学成因联系。

Slip rates of typical active faults were estimated and eastward motion of the crust was analyzed in the middle part of Tibetan Plateau based on large-scale geological survey and dating of active faults along the Golmud-Lhasa Railway. NW-NWW-EW trending Late Quaternary active faults were identified in the middle part of Tibetan Plateau. Active faults such as Kunlun, Hohxil, Tongtianhe, Bengcuo, Nianqingtanghla and Yaluzangbu had 6～10 mm/a average slip rates, Fenghuoshan, Wuli and Yanshiping had 3～4 mm/a average sliprates, whereas Tanggula and Gelincuo had 2 mm/a average slip rates in Late Pleistocene-Holocene. Since Late Pleistocene, the crust in the middle part of Tibetan Plateau has experienced evident eastward motion relative to the Qaidam block, with the eastward motion rate increasing gradually from both sides to central Tibetan Plateau and reaching 40 mm/a in the Tanggula Range. The displacement of active faults and the eastward crustal motion are very likely to have been caused by the coherence of S-N compression and the eastward shearing within the crust in Tibetan Plateau.