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... In this study, we document a previously unreported domain of active faulting and Quaternary basin development in the southern Beishan region. Three small NE-trending basins with Quaternary infill are documented; the easternmost and largest of the four basins is called the Jiujing Basin ( Figure 2) [11,14,15]. The origin of the Jiujing Basin in the wider context of the Late Cenozoic reactivation of the southern Beishan is the subject of our study (Figure 1). ...
... Hongqishan fault zone (HQSF) to the south and Jinmiaogou fault zone (JMGF) to the north (Figures 2 and 3(a), [14,15]). Statistical analysis of the strike of 681 subfaults between the HQSF and JMGF fault zones shows a dominant NEtrending distribution (insert map in Figure 3(a)). ...
... The NE-striking Jiujing fault system and Jiujing Basin are located within a 15-20 km-wide stepover zone between the E-W-striking HQSF and JMGF. The Jiujing fault (JJF) cuts across bedrock and range-front basin sediments forming offset gullies and risers, fault scarps, triangular facets, and knickpoints [14,15]. At the southern tip of the JJF, subdued topography limits the development of stream gullies; thus, evidence for strike-slip displacements along the fault that might be revealed by drainage offsets was not identified. ...
We present results from a multidisciplinary investigation of the Jiujing fault (JJF) system and adjacent Jiujing Basin in the southern Beishan block, western China. Structural and geomorphological fieldwork involving fault and landform investigations, remote sensing analysis of satellite and drone imagery, analysis of drill-core data, paleoseismological trench studies, and Quaternary dating of alluvial sediments suggest the JJF is a late Pleistocene to Holocene oblique sinistral-slip normal fault. Satellite image analysis indicates that the JJF is a connecting structure between two regional E-W-trending Quaternary left-lateral fault systems. The Jiujing Basin is the largest and best developed of three parallel NE-striking transtensional basins within an evolving sinistral transtensional duplex. Sinistral transtension is compatible with the orientation of inherited basement strike belts, NE-directed SHmax, and the modern E-NE-directed geodetic velocity field. Cosmogenic 26Al/10Be burial dating of the deepest sediments in the Jiujing Basin indicates that the basin began to form at ~5.5 Ma. Our study reveals a previously unreported actively deforming domain of transtensional deformation 100 km north of Tibet in a sector of the Beishan previously considered tectonically quiescent. Recognition of latest Miocene-Recent crustal reactivation in the Jiujing region has important implications for earthquake hazards in the Beishan and western Hexi Corridor/North Tibetan foreland sectors of the Silk Road Economic Belt. Additionally, we compare the timing of latest Miocene-Recent crustal reactivation in the southern Beishan with the documented onset of reactivation in other deforming regions north of Tibet.
... The south part of the Beishan Block is mainly composed of the Late Paleozoic-Mesozoic strata and the scattered Proterozoic strata (Fig. 2). The dominant deformation in the Beishan Block is north- south contraction accompanying with east-west extension since the Late Quaternary ( Wang et al., 2004). From the Northern Qilian Mountains to the Beishan Block, the geologic units along the MT profile are distinct in geomorphology. ...
Controversies exist on the tectonic models at the northern margin of the Qinghai-Tibetan Plateau. New magnetotelluric (MT) data, with a bandwidth of 0.001–5827.5 s, were collected along one profile starting from the Northern Qilian Mountains in the southern end, crossing the Hexi Corridor, the Kuantan Shan-Hei Shan uplift, the Huahai Basin, and coming into the Beishan Block. Two-dimensional (2D) and three-dimensional (3D) resistivity models of the data are derived using magnetotelluric inversion codes. The 2D models, and the electrical structures along the profile extracted from the 3D models, are comparable and complementary in defining reliable scales and shapes of anomalies in electrical resistivity. The crust-upper mantle structures beneath the northern plateau are characterized by two imbricated southward underthrusted blocks of continental crust or lithosphere. The Northern Qilian Fault is interpreted as a gently south-dipping décollement in the upper crust along the top of a high resistivity body below the Northern Qilian Mountains. The two high resistivity bodies below the Kuantan Shan-Hei Shan uplift are disconnected; the upper crustal one may connect with the high resistivity basement below the Northern Qilian Mountains in that the attitudes and deformations of the strata at these areas are coherent; whereas the lower crust-upper mantle one may be the cold lithospheric materials of the block north to the Hexi Corridor and that forms a south-dipping boundary between the Hexi Corridor and its northern neighbors. The observed high electrical resistivity beneath the Beishan Block provides further support for the notion that the Beishan Block should be rigid as a whole; only in this manner could it transfer stress from south to north. The northern boundary of the Qinghai-Tibetan Plateau is below the Kuantan Shan-Hei Shan Fault and underthrusting of continental crust or lithosphere is the main cause for the thickening of the plateau crust in the north.
On the north side of the Hexi Corridor, two active faults, which belong to two different fault systems, have been discovered on the southern margin of Beishan, namely the Jiujing-Bantan fault and the Ebomiao fault. The NE-trending (40°~50°) Jiujing-Bantan fault with a NW-trending dip angle of 60° ~ 70° is ~ 28 km long and ~55 km away from Yumen City. It consists of 4 branches and presents a complex Y-shaped distribution, controlling the development of the two late Pleistocene basins on its west side. The nearly EW-trending Ebomiao fault with a NW-trending dip angle of 60°~80° is ~18 km long and ~50 km away from Jinta County. Base on results from the satellite image interpretation, offset geomorphological survey, trench excavation and optical luminescence dating, we discovered a series of ridges, gullies and terraces offset by the Jiujing-Bantan fault which has been active since ~20 ka ago mostly with normal left-lateral strike-slips. The northward thrusting of the Ebomiao fault formed a clear linear scarp and offset the gullies with left-lateral strike-slips. This fault has been active since ~30 ka ago, mainly with reverse left-lateral strike-slips. The neotectonic activities of these two faults evidences that the long-range strain transmission from the northern margin of the Tibetan Plateau has entered into the southern margin of the Beishan orogenic belt since the late Cenozoic.
在河西走廊北侧、北山南缘新发现属于不同断裂系统的两条晚第四纪活动断裂, 分别称之为旧井-板滩断裂和俄博庙断裂。其中, 旧井-板滩断裂长约28 km, 距玉门市约55 km, 由4 条分支断裂组成, 呈复杂的“ Y” 字形分布。总体走向北东40°~50°, 倾向北西, 倾角60° ~ 70°, 控制了西侧两个晚新生代 盆地的发育。俄博庙断裂长约18 km, 距金塔县城约50 km, 走向近东西, 倾向北西, 倾角60° ~ 80°。根据卫星影像解译、断错地貌调查、探槽开挖和光释光测年结果, 旧井-板滩断裂断错了一系列山脊、冲沟和阶地, 在距今约2 万年以来有过活动, 以正左旋走滑为主; 俄博庙断裂北向逆冲形成清晰的线性陡坎,并左旋断错了冲沟, 在距今约3 万年以来有过活动, 以逆左旋走滑为主。以上两条断裂的新构造活动揭示了青藏高原北缘晚新生代以来的远程应变传递已经进入北山造山带南缘。
Fault influenced zone is one of the key factors in site selection and design for high-level radioactive waste repository. Field survey and chart analysis were used to obtain the relationship between the fault distance and mean length of traces, the midpoint density of both sides of fault. When the distance increases, the mean trace length increases and the midpoint density decreases. The correlations obey a negative exponential function. When the distance exceeds the width of the fault influenced zone, the mean trace length and the midpoint density fluctuate at a certain value. Accordingly, both sides of the fault can be divided into two regions: serious influenced zone I and influenced zone II. The width of the maximum influenced zone and the distribution are markedly different among different fault types, the one of the normal fault is the smallest, the one of the strike-slip fault is the second, and the one of the reverse fault is the largest. Meanwhile, the influenced zone of the strike-slip fault shows a symmetrical distribution, and the normal and reverse faults show asymmetrical distribution. The width of fault influenced zone and the length of fault obey a power function approximatively.
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