Active normal faulting and the seismogenic fault of the 1739 M ∼8.0 Pingluo earthquake in the intracontinental Yinchuan Graben, China

The NNE-trending Yinchuan Graben is one of several intracontinental grabens that have developed in the extensional environment around the Ordos Block, northern-central China, and is bounded by active normal faults at both its eastern and western margins. In this study, we present new evidence for the Holocene activity and paleoseismicity of the active normal faults developed in the Yinchuan Graben. Interpretations of high-resolution WorldView and Google images, field investigations, trench excavations, seismic data, and radiocarbon dating results reveal the following: (i) two main active fault zones, the Helanshan Piedmont Fault Zone (HPFZ) along the western margin of the graben and the Huanghe Fault (HHF) along the eastern margin, are characterised by conspicuous fault scarps developed on both Holocene alluvial fans and terrace risers; (ii) the active faults are dominated by normal faulting; (iii) the Holocene normal slip rate is estimated to be ∼2–3 mm/yr, and the recurrence interval of morphogenic earthquakes is estimated to be ∼1500–2000 yr for both the HPFZ and HHF; and (iv) the HHF is the most likely seismogenic fault for the triggering of the 1739 M ∼8.0 Pingluo earthquake. Our results show that the HPFZ has the potential to produce a destructive earthquake in the near future, because no large earthquake has occurred on this fault during the past ∼1500 years. This contrasts with previous findings that the fault scarps of the HPFZ were caused by the 1739 Pingluo earthquake and that therefore the likelihood of a large and destructive earthquake on that fault in the near future is relatively small because of the <300 years elapsed since the earthquake. Therefore, it is necessary to reconstruct the model of faulting, tectonic activity, and paleoseismicity of the intracontinental graben and to reassess the seismic hazard of the active normal faults for the densely populated Yinchuan region

Reevaluation of the offset of the Great Wall associated with the ca. M 8.0 Pingluo earthquake of 1739, Yinchuan graben, China

In this study, we reevaluate, based on our investigation, the ground deformation caused around the area of the Great Wall by the ca. M 8 Pingluo earthquake of 1739 along an active fault zone in the Yinchuan graben, on the western margin of the Ordos Block in northern central China. Previous studies have shown that the Great Wall of China was damaged and right-laterally offset by the 1739 M 8 Pingluo earthquake up to ∼1.6–2 m, with a 0.1–1.9-m vertical component, at three locations. However, our recent fieldwork and in-situ measurements have shown that the Great Wall was not affected by the ca. M 8 Pingluo earthquake of 1739, as reported previously, but was actually built on preexisting active fault scarps. This study reinterprets the offset of the Great Wall based on these new field observations and attempts to identify the seismogenic source fault that triggered the 1739 Pingluo earthquake. More work is required if we are to better understand the deformation characteristics of the seismogenic source fault and also improve our ongoing assessments of the seismic hazard within the densely populated area of the Yinchuan graben, central China

Fission track ages and Mesozoic tectonic uplift in the Niushoushan-Luoshan area on the western edge of the Ordos Basin

The western margin of the Ordos Basin and its adjacent regions have undergone a complex tectonic evolution from the Mesozoic to the Cenozoic era. However, the question of tectonic uplift since the Cenozoic era remains a topic of contention, and the regional thermal evolution history necessitates precise chronological evidence. Situated close to the thrust belt within the western margin of the Ordos Basin, the Niushoushan-Luoshan area holds pivotal significance in unraveling the Mesozoic tectonic events within the basin's confines. Through a meticulous exploration employing apatite fission track (AFT) analysis and thermal history simulation, this study delineates the Mesozoic uplift sequence and its temporal confines in the Niushoushan-Luoshan area. The results reveal that the Mesozoic uplift within this region predominantly occurred during the Middle Jurassic period (170 Ma) to the end of the Early Cretaceous (110 Ma). Furthermore, we observe a slightly earlier onset of uplift in the Luoshan area (170 Ma) compared to the Niushoushan area (160 Ma). This uplift is primarily attributed to the north-eastward extrusion of the Qilian orogenic belt. Combining our findings with existing research, we propose that the Cenozoic uplift in the western margin of the Ordos Basin and its adjacent areas started during the Late Triassic, comprising two distinct phases: the first phase unfolding from the Late Triassic (220 Ma) to the end of the Early Jurassic (185 Ma), and the second phase occurring from the Middle Jurassic (175 Ma) to the end of the Early Cretaceous (110 Ma); the uplift in the Niushoushan-Luoshan area is part of the second phase of uplift along the western margin of the Ordos Basin. The two Cenozoic tectonic uplift phases along the western margin of the Ordos Basin display characteristics of north-to-south and southwest-to-northeast propagation, respectively. It is inferred to be associated with the Late Triassic collision between the North China and South China blocks, as well as the movement of the Lhasa Block converging toward the northeast during the Middle to Late Jurassic

Provenance and tectonic significance of late Mesoproterozoic detrital zircons from the Tonian system, northern margin of the North China Craton

<p>The involvement of the North China Craton (NCC) in the assembly or breakup of Rodinia has long been debated. Studies of palaeomagnetism, mafic sills (dikes), igneous events, and sedimentary records have led to contrasting opinions on this topic. No igneous events related to the late Mesoproterozoic assembly of Rodinia have been reported in the NCC. However, the authors found numerous late Mesoproterozoic zircons in the Tonian system on the northern margin of the NCC. The Tonian Zhulazhagamaodao formation is composed of meta-sandstone, siltstone, slate, carbonate, and dolomine of the littoral to neritic facies and occurs mainly in the western part of the Bayan Obo–Zhaertai–Langshan rift. U–Pb dating of detrital zircons from the Tonian system reveals age peaks at 1079 ± 23 Ma, 1092 ± 22 Ma, 1175 ± 50 Ma, 1175 ± 18 Ma, 1260 ± 45 Ma, 1266 ± 16 Ma, and 1270 ± 26 Ma, which correspond to the timing of Rodinia assembly. Considering that coeval igneous rocks and orogenic belts developed mostly in the Laurentia–Baltica cratons, we propose that these cratons supplied clastic material to the northern margin of the NCC and that they had a close spatial relationship between each other during the Tonian.</p