摘要
喀喇昆仑断裂(KKF)在普兰裂谷以东的存在状况有两种推论:1大陆逃逸模式,认为喀喇昆仑断裂的活动状况在普兰裂谷以东和以西没有差别,都是沿雅鲁藏布江缝合带经历长时间、大尺度的右旋走滑;2分散变形模式,认为喀喇昆仑断裂的活动终止于普兰裂谷,断裂的走滑错距均被普兰裂谷吸收。然而,长久以来并没有针对喀喇昆仑断裂在普兰裂谷以东活动的野外调查。近年来,在普兰—仲巴一线针对喀喇昆仑断裂展开了详细的断裂几何学、运动学和年代学研究。野外调查表明,普兰—仲巴一线断层活动的构造地貌特征显著,如线性排列的断层三角面和断层陡坎、断塞塘、错断脊以及不同级别的水系右旋弯曲等,表明活动的喀喇昆仑断裂不仅仅局限于普兰裂谷以西。冲沟和错断脊显示霍尔地区喀喇昆仑断裂最大右旋错距为(11±1)km,而马攸木山以东的冈底斯花岗岩被右旋错断(7±1)km。喀喇昆仑断裂不同断层分支在马攸木山侧接,形成局部的挤压区。该挤压区吸收了约4km的走滑错距,造成马攸木山成为雅鲁藏布江和印度河的分水岭。仲巴地区罗布岗日峰以东,喀喇昆仑断裂失去其地表踪迹,表明马攸木山附近的7km走滑错距完全被隆格尔裂谷—罗布岗日峰—琼果盆地组成的盆山体系所吸收。霍尔附近一个右旋错距(84±2)m的错断脊光释光测年结果表明该错断脊形成于(9.4±0.8)^(21.7±1.6)ka,由此计算出喀喇昆仑断裂在本区的最大右旋走滑速率为每年(4.0±0.3)mm。如果晚新生代以来喀喇昆仑断裂在本区均保持这样的走滑速率,则喀喇昆仑断裂在普兰—仲巴一线的起始活动时间在3 Ma左右,远小于阿里地区喀喇昆仑断裂的12 Ma起始活动时间。因此,断裂在研究区的几何学、运动学和年代学特征表明喀喇昆仑断裂在青藏高原陆内变形中具有分散变形的构造模式特征。
The existence active slip along Karakorum fault （KKF） in the east of Pulan graben is debated. One interpretation is that the KKF extends eastward along the Indus-Yalu suture zone and accommodates large magnitudes right-lateral shear; another interpretation is that the displacement along the KKF is absorbed by structures bounding Pulan graben and Gurla Madhata detachment system. The kinematic and geometric characteristics of the KKF along a 400 km long segment of the Indus-Yalu suture zone between Mt. Kailas and Lopugangri ranges were reported. The results show that the evidence of recent deformation is characterized by offset streams, fault scarps, sag ponds, and shutter ridges; streams show a consistent right-lateral deflection; offsets vary from as little as tens of meters to as much as （11±1）km, and basement rocks also show the same sense of offset with （7±1）km; a region of transpression at Mayoumu Pass is interpreted to have absorbed 4 km of right-lateral displacement along the KKF, and about 7 km offset is transferred to Darong-Qiongguo Basin and possibly as far east as Lopugangri Range; a Holocene slip rate of （4.0±0.3）mm per year for this segment of the KKF is calculated based on （84±2）m right-lateral shutter ridge offset and optically stimulated luminescence ages of samples from sands and clays in the ridge ranging from （9.4±0.8）ka to （21.7±1.6）ka; the KKF is interpreted to have propagated to south-central Tibet since 3 Ma if the （11±1）km offset occurs at Holocene slip rate keeping steady since Pliocene; right-lateral shear along the KKF in the western Himalaya is comparable to the distributed left-lateral shear documented from Dinggye to Chigu Co along the Indus-Yalu suture zone in the eastern Himalaya. It is suggested that this spatial distribution of strike-slip deformation is best explained by active oroclinal bending of Himalayan thrust wedge.
出处
《地球科学与环境学报》
CAS
2016年第4期483-493,共11页
Journal of Earth Sciences and Environment
基金
国家自然科学基金项目(41172192)
中国地质调查局地质大调查项目(121201101000150014)
关键词
喀喇昆仑断裂
冈底斯花岗岩带
错断脊
水系位错
构造地貌
光释光测年
走滑速率
Karakorum fault
Gangdise granite belt
shutter ridge
stream channel offset
geomorphic evidence
optically stimulated luminescence
slip rate
