走滑断裂百万年时间尺度位移量估计及其在阿尔金断裂系中的应用  

Estimation of displacements along strike-slip fault on a million-year timescale:A case study of the AltynTagh fault system

作　　者：黄飞鹏 张会平[1] 熊建国 赵旭东 HUANG Feipeng;ZHANG Huiping;XIONG Jianguo;ZHAO Xudong(State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration,Beijing 100029,China)

机构地区：[1]中国地震局地质研究所地震动力学国家重点实验室,北京100029

出　　处：《地质力学学报》2021年第2期208-217,共10页Journal of Geomechanics

基　　金：国家自然科学基金项目(41761144071);第二次青藏高原综合科学考察研究项目(2019QZKK0704)。

摘　　要：断裂滑动速率不仅是新生代构造定量研究的重要参数之一,也是地球动力学研究的重要组成部分。但现有研究普遍缺乏介于长时间尺度(>Ma)地质体累积位移和短时间尺度(晚第四纪以来)地貌单元位错以及年—十年尺度的大地测量观测之间的断裂位移量,从而造成了理解百万年时间尺度下断裂演化历史的空区。由于走滑断裂破坏了山前洪积扇与其汇水盆地组成的系统,残留的断错洪积扇会沿断裂走向在空间上不均匀地展布。据此提出3种利用断错洪积扇确定走滑断裂大规模累积位移量的方法。第一,洪积扇面积与汇水盆地面积一般符合A_(f)=γA _(c)(A_( f)为洪积扇面积,A_(c)为汇水盆地面积,γ为常数0.5±0.35)对应关系,利用二者之比是否异常,获得断裂位错流域盆地走滑位移量;第二,利用断裂两盘的河流上下游分布相同岩性矿物组分,识别两盘对应地貌单元获得走滑位移量;第三,利用地貌单元残留标志与上游物源河道进行对比,估算走滑位移。同时,将上述3种方法应用于研究阿尔金断裂系百万年时间尺度以来的走滑位移量实例中,在现有速率分布前提下,可估算出地貌体的形成年龄,进一步验证了文中提出的走滑位移量估计方法能为精确厘定走滑断裂百万年尺度的演化历史提供新的解决途径和技术方法。Fault slip rate matters not only as one of the important parameters for quantitative study of Cenozoic tectonics but also a key element in geodynamic research.However,most studies have focused on the long-term(>Ma)cumulative displacement of geological mass,short-time(since the late Quaternary)dislocation of geomorphic units as well as annual-decadal geodetic observations,and few people studied the fault displacement on a timescale in between,leaving a gap in understanding the evolutionary history of fault on a million-year timescale.Since the strike-slip fault breaks the system of alluvial fans and their catchment basins,causing the spatially uneven distribution of residual offset alluvial fans along the fault direction,we proposed three methods to determine the large-scale cumulative displacement of strike-slip fault based on the offset alluvial fans.The first method commonly presents a correspondence between the alluvial-fan area and catchment basin area as A_(f)=γA_(c)(A_(f) is the alluvial-fan area,A_(c) is the catchment basin area,γ is a constant 0.5±0.35),which leads us to determine the strike-slip displacement of the offset basin by identifying whether the correspondence is unusual.The second method helps us to get the strike-slip displacement by distinguishing geomorphic units with the same lithological mineral components distributed at both sides of the fault.The third is to measure the strike-slip displacement by comparing the residual geomorphic unit with the corresponding stream outlet.In this study,we applied the above three methods to study the strike-slip displacement of the AltynTagh fault system on a million-year timescale,and to estimate the formation age of these geomorphic units based on the exiting fault slip-rate.It is further verified that the estimation methods proposed in this paper can provide a new angle and technical solution to accurately determine the evolution history of the strike-slip fault on a million-year scale.

关 键 词：断裂滑动速率 累积位移 洪积扇 走滑断裂 阿尔金断裂系 

分 类 号：P315.2[天文地球—地震学]