佛洞庙-红崖子断裂属于祁连山北缘断裂带中段逆冲推覆的前锋断裂,也是酒东盆地与祁连山之间的边界逆断裂.断裂运动学速率的准确限定对于理解青藏高原现今构造变形机制及其区域地震危险性至关重要.文中选取该断裂中、西段丰乐河口、石羊圈2个地点,通过地质地貌填图,综合应用地形剖面测量、光释光定年、宇宙成因核素定年和1℃定年等手段,获得了约40ka以来的断裂平均垂直滑动速率约为1.1 mm/a;考虑到断裂倾角为40°～50°,平均缩短速率为0.9～1.3mm/a.跨酒东盆地的GPS速度剖面给出的酒东盆地10a尺度缩短速率约为1.4mm/a,与地质缩短速率1.0～1.5mm/a几乎一致;酒东盆地内部的隐伏断裂或褶皱变形也可能吸收部分地壳缩短.酒东盆地总体地壳缩短速率约占整个祁连山造山带缩短速率的%,高原向NE方向扩展的前锋带现今仍具有强烈的地震活动性.%The Fodongmiao-Hongyazi Fault belongs to the forward thrust fault of the middle segment of northern Qilian Shan overthrust fault zone,and it is also the boundary between the Qilian Shan and Jiudong Basin.Accurately-constrained fault slip rate is crucial for understanding the present-day tectonic deformation mechanism and regional seismic hazard in Tibet plateau.In this paper,we focus on the Shiyangjuan site in the western section of the fault and the Fenglehe site in the middle part of the fault.Combining geomorphic mapping,topographic surveys of the deformed terrace surfaces,optically stimulated luminescence(OSL) dating,terrestrial cosmogenic nuclide dating and radiocarbon (14C)dating methods,we obtained the average vertical slip rate and shortening rate of the fault,which are ～1.lmm/a and 0.9 ～ 1.3mm/a,respectively.In addition,decadal GPS velocity profile across the Qilian Shan and Jiudong Basin shows a basin shortening rate of～ 1.4mm/a,which is consistent with geological shortening rates.Blind fault or other structural deformation in the Jiudong Basin may accommodate part of crustal shortening.Overall crustal shortening rate of the Jiudong Basin accounts for about 1/5 of shortening rate of the Qilian Shan.The seismic activity of the forward thrust zone of Tibetan plateau propagating northeastward is still high.
展开▼
