青藏高原东缘新生代隆升剥露与断裂活动的低温热年代学约束

Cenozoic exhumation and fault activities across the eastern Tibet:constraints from low-temperature thermochronological data

青藏高原东缘作为高原生长的东边界,其新生代以来隆升剥露与扩展模式备受关注.高原内部平缓的地貌和边界构造带不显著的缩短变形被认为是下地壳流作用的重要证据.然而近年来,越来越多的低温热年代学研究结果表明,中-晚新生代以来跨不同断裂带存在显著的差异性隆升剥露,指示了断裂体系在青藏高原东缘构造变形与演化中的重要作用.本文系统收集区域内现有不同封闭温度体系的低温热年代学数据,综合分析结果表明青藏高原东缘隆升剥露及生长扩展与整个高原抬升具有准同步性.最为广泛和显著的剥露主要发生在~30 Ma以来,且高原东缘的最大侵蚀量区受控于断裂活动,快速侵蚀带的空间分布与鲜水河断裂带相一致.在区域尺度上,现有数据所揭示的剥露事件启动、持续时间及速率的显著差异性揭示了断层活动对青藏高原东缘地表剥露过程的控制作用.本文提出青藏高原向东扩展是多阶段、非均匀过程,新生代以来不同断裂带在青藏高原向东扩展过程中起到了至关重要的作用,不支持“下地壳流假说”强调的“东缘上地壳变形不显著”的认识.

The growth pattern of the eastern Tibet is still mysterious,where the remnant upland with low relief has been hypothesized as the response to lower crustal flow originating from the over-thickened crust of central Tibet.In recent decades,however,a growing number of low-temperature thermochronological studies have revealed a striking different sight.In this paper,we collected the apatite and zircon(U-Th)/He and fission track ages across the eastern Tibet,and found where the exhumation type is quasi-synchronized with the entire plateau uplift,the early uplift and exhumation occurred mainly in the fault zone,the most extensive and rapid exhumation process is occurred since^30 Ma and the fault system controlled the magnitude of exhumation,the Xianshuihe fault represent the rapidest erosion zone.The significant differences in the time and duration of these events,and the exhumation rates indicate the faulting mainly controls the pattern of surface process.Moreover,the multi-stage,differential denudation process across the eastern Tibet challenge the lower crustal flow model.