NEW DISCOVERY OF XIARIHA FAULT ZONE AROUND DULAN AREA, QINGHAI PROVINCE AND ITS TECTONIC IMPLICATIONS

doi:10.3969/j.issn.0253-4967.2021.03.009

Abstract

Abstract: The deformation pattern in the northeastern margin of Tibetan plateau is characterized by NE compression, clockwise rotation and eastward extrusion, forming the NNE trending dextral strike-slip faults which further divide the region into several sub-blocks. The deformation of Qaidam secondary block is dominant by northwestward extrusion and rotation, which is controlled by the Elashan and East Kunlun faults. However, the deformation style of Dulan area, the junction of these two faults, remains unclear. We discovered a new active fault zone with a length of 60~70km west to Elashan Fault during our recent field geological survey around Dulan area, named Xiariha fault zone(XFZ), which is a dextral strike-slip fault zone trending NW, consisting of the Xiariha and Yingdeerkang faults. According to the remote sensing interpretation and field investigation, it is found that the Xiariha fault zone showed distinct linear characteristics, reverse scarp, sag pond and ridge dislocation on the satellite images and displaced multi-levels of alluvial fans and river terraces. According to previous studies, the exposed age of T1 terraces is Holocene in the Elashan area, which is located at east of Dulan. During the field investigation, we used the unmanned aerial vehicle(UAV)to get the fine geomorphology features along the XFZ. Also, to define the active era, we tried to find the fault section of the XFZ that could provide the information of the contact between the fault and late Quaternary strata. Based on the high-resolution DEM obtained by UAV, the offset of T1 is about 2.5m, indicating its activity in Holocene compared with the Elashan area. Along the XFZ, the fault displaced late Quaternary strata revealed on the section. The geomorphic features and fault section show that the XFZ is a late Pleistocene to Holocene active fault. The Dulan area is located at the convergence of East Kunlun Fault and Elashan Fault, the southeastern end of Qaidam secondary block, which is affected by the regional NE and SW principal compressive stress and shear stress. Under this circumstance, the Qaidam block is experiencing extrusion and rotation and there are a series of NW-trending dextral strike-slip faults parallel to the Elashan Fault and EW-trending sinistral strike-slip faults parallel to the East Kunlun Fault, such as Reshui-Taosituo River Fault, developed in the Dulan area. Therefore, we suggest that the Xiariha Fault and the nearly EW trending, Holocene sinistral Reshui-Taosituo River Fault adjust the extrusion rotation deformation jointly at the southeast end of the Qaidam block under the control of the Elashan Fault and the East Kunlun Fault, respectively. Meanwhile, the new discovery of Xiariha Fault and its activity in Holocene is not only of great significance to understand the regional tectonic deformation model, but also leads to a great change in the understanding of regional seismic risk because of its capabliliby of generating strong earthquakes. Therefore, it is urgent to carry out further research work in this area, improve the understanding of regional strain distribution mode, and provide reference for regional seismic safety issues.

Key words: northeast margin of Tibetan plateau, Qaidam block, Xiariha fault zone, tectonic deformation, seismic risks

摘要： 青藏高原东北缘地区的构造变形以NE向挤压缩短、顺时针旋转和向E挤出为主要特征, 在NE向挤压作用下形成了NNW向的右旋走滑断裂, 进一步将东北缘地区分为多个次级块体。其中, 鄂拉山断裂与东昆仑断裂围限形成的柴达木次级块体整体以向NW方向的旋转挤出为主要特征, 但处于这2条边界断裂交会部位的柴达木盆地东缘都兰地区的构造变形方式却不清楚。近期在针对都兰地区的野外地质调查中, 发现了一条NW走向、长60~70km的右旋走滑断裂带, 即夏日哈断裂带。该断裂带位于鄂拉山断裂西侧, 由2条近平行的断裂组成, 分别为夏日哈断裂和英德尔康断裂。经遥感解译与野外地质调查发现, 该断裂线性特征明显, 断错了多期冲积扇、河流阶地等晚第四纪地质地貌体, 发现了多个断错晚第四纪沉积物的剖面, 显示该断裂带为晚更新世—全新世活动断裂。综合分析认为, 该断裂与前期发现的近EW走向的热水-桃斯托河全新世左旋走滑断裂, 分别在鄂拉山断裂和东昆仑断裂的影响下共同调节柴达木块体端部的挤出旋转变形。同时, 该断裂为该区新发现的活动断裂, 具有中强地震的潜在发震能力, 这不仅对理解区域构造变形模式具有重要意义, 也导致对该区域地震危险性的认识发生较大改变。因此, 亟待在该区域开展更进一步研究工作, 以增进对区域应变分配模式的理解, 为区域地震安全问题提供参考。

关键词: 青藏高原东北缘, 柴达木块体, 夏日哈断裂带, 构造变形, 地震危险性

CLC Number:

P315.2

HA Guang-hao, REN Zhi-kun, LIU Jin-rui, LI Zhi-min, LI Zheng-fang, MIN Wei, ZHOU Ben-gang. NEW DISCOVERY OF XIARIHA FAULT ZONE AROUND DULAN AREA, QINGHAI PROVINCE AND ITS TECTONIC IMPLICATIONS[J]. SEISMOLOGY AND GEOLOGY, 2021, 43(3): 614-629.

哈广浩, 任治坤, 刘金瑞, 李智敏, 李正芳, 闵伟, 周本刚. 青海都兰地区夏日哈活动断裂带的发现及其构造意义[J]. 地震地质, 2021, 43(3): 614-629.

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