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Abstract The Wuhai Basin is located in the northwestern corner of the Ordos Block. Analyzing the geometry, along with the kinematic and dynamic characteristics of the boundary fault, the Zhuozishan West Piedmont Fault (ZWPF), will elucidate the regional tectonic environment and guide earthquake prevention and disaster reduction projects. Six representative sites were selected for topographic measurements, from the northern, middle and southern parts. Displacements of the ZWPF were calculated by measuring the top surface elevation of a widely distributed lacustrine layer in the footwall from outcrops at each site, and from boreholes in the hanging wall. The vertical slip rate of the ZWPF was then calculated based on the displacement and age of the lacustrine layer. Three to four normal fault-controlled terraces have developed on the footwall of the ZWPF, and the top surface of the lacustrine layer is at 1092–1132 m elevation. Data from boreholes showed that the top surface of the lacustrine layer is at an elevation of 1042–1063 m in the hanging wall. Vertical slip rates since 70 ka were estimated as 0.5 ± 0.2 to 1.0 ± 0.2 mm/a. The highest rate of vertical slip was observed at Fenghuang Ridge, in the central part of the fault system, and decreased to the south. In the northern Wuhai Basin, normal faulting still controls the piedmont landscape. However, NW-SE trending reverse faults and secondary folding have resulted from dextral strike-slip movement of the fault. The Wuhai Basin developed as a dextral-tensional negative flower structure. This study indicates that stress conditions of the northwestern margin of the Ordos Block include NE–SW compression and NW–SE extension, and an S-shaped rift zone has dominated the scale, structure, and evolution of the Yinchuan, Wuhai, and Hetao Basins, along with the active mode of faulting in these basins. Highlights • Vertical slip rates between 0.5 ± 0.2 and 1.0 ± 0.2 mm/a were calculated for the ZWPF. • The ZWPF has a larger strike-slip rate, resulting in development of reverse faults. • The Wuhai Basin has developed a dextral- tensional negative flower structure. • Stress conditions and S-shaped distribution dominate the development of basins. [ABSTRACT FROM AUTHOR]

Considerable post-breakup extensional deformation is recorded in the continental margins of the South China Sea (SCS). To recognize the nature and origin of the significant deformation during the syn-spreading stage (32-15.5 Ma) in the SCS, we comprehensively analyzed the geometry and kinematics of the faults and contemporaneous magmas in the Baiyun sag, northern margin of the SCS, using high-resolution regional three-dimensional seismic data. The kinematic analyses indicate that the faults in the Baiyun sag are recently formed following the onset of seafloor spreading in the SCS. The faults exhibit multiple episodes of growth history, with three active episodes, 32-29, 23.8-21 and 18.5-16.5 Ma, separated by periods of inactivity. Four volcanic groups comprising 98 volcanic mounds have been identified and described, located separately in the northwestern, the central, the southeastern and the northern slope areas. The occurrence of multiple palaeo-seafloors, complemented by the biostratigraphic and K-Ar dating data, reveals multiple extrusive events of the syn-spreading magmas in the Baiyun sag, with three active periods of 23.8-21, 18.5-17.5 and 17.5-16.5 Ma. This study confirms that the normal faulting has a shared genetic origin with the contemporaneous magmatism during the syn-spreading stage in the deep-offshore Baiyun sag, northern margin of the SCS. The episodic fault growth and magmatic extrusive events reveal that the Baiyun sag has undergone at least three episodic tectonic events during the syn-spreading stage, which evolved in response to the multi-stage seafloor spreading of the SCS. [ABSTRACT FROM AUTHOR]

On January 21st, 2016, a Ms 6.4 earthquake hit Menyuan County, Qinghai province, China. The nearest known fault is the Leng Long Ling (LLL) fault which is located approximately 7 km north of the epicenter. This fault has mainly shown sinistral strike-slip movement since the late Quaternary Period. However, the focal mechanism indicates that it is a thrust earthquake, which is different from the well-known strike-slip feature of the LLL fault. In this study, we determined the focal mechanism and primary nodal plane through multi-step inversions in the frequency and time domain by using the broadband regional seismic waveforms recorded by the China Digital Seismic Network (CDSN). Our results show that the rupture duration was short, within 0–2 s after the earthquake, and the rupture expanded upwards along the fault plane. Based on these fault parameters, we then solve for variable slip distribution on the fault plane using the InSAR data. We applied a three-segment fault model to simulate the arc-shaped structure of the northern LLL fault, and obtained a detailed slip distribution on the fault plane. The inversion results show that the maximum slip is 0.43 m, and the average slip angle is 78.8°, with a magnitude of Mw 6.0 and a focal depth of 9.38 km. With the geological structure and the inversion results taken into consideration, it can be suggested that this earthquake was caused by the arc-shaped secondary fault located at the north side of the LLL fault. The secondary fault, together with the LLL fault, forms a normal flower structure. The main LLL fault extends almost vertically into the base rock and the rocks between the two faults form a bulging fault block. Therefore, we infer that this earthquake is the manifestation of a neotectonics movement, in which the bulging fault block is lifted further up under the compresso-shear action caused by the Tibetan Plateau pushing towards the northwest direction. [ABSTRACT FROM AUTHOR]

The northwestern margin of the Hetao Graben, North China, is bounded by a pronounced 160-km-long Langshan Piedmont fault (LPF). The kinematics and recent tectonic activity of this rift-border fault and its accommodated extensional strain can help us better assess the seismic potentials. In this study, on the basis of high-resolution satellite images, digital elevation models acquired by small unmanned aerial vehicles using structure-for-motion techniques, field observations, and radiocarbon (14C) age dating, we demonstrate that (1) the LPF is a Holocene active normal fault with an average dip of ~607; the extension rate is estimated to be ~0.4-0.7mm/y, lower than geodetic strain rate; (2) the ongoing tectonic activity along this fault has played a significant role in controlling the present topography of the Langshan Mountains and neighboring areas; (3) slip partitioning probably occurred in the western Hetao Graben; namely, normal slip dominated the basin-bounding faults, and right-lateral slip occurred on the buried faults within the flat-lying graben. We suggest that precisely determined fault slip rates and geometry are needed with the aim of further quantifying the extensional strain distribution. The results of this study would be helpful in achieving a better understanding of fault development and evolution in actively extending regions. [ABSTRACT FROM AUTHOR]

The North China Plate (NCP) underwent multi-phase intracontinental deformation during the Mesozoic, which is a much-debated research subject. Here we present a case study of this deformation inferred from regional-scale Helanshan superposed folds in the west of the NCP. New structural analyses and fault kinematic analyses in the Helanshan Structural Belt (HSB) indicate a two-stage syn-folding paleo-stress field, comprising early NNE–SSW compression, with mean orientations 190°/01° (plunge direction/plunge) for σ 1 , 283°/26° for σ 2 , and 100°/63° for σ 3 , and later WNW–ESE compression with mean orientations of σ 1 , σ 2 , and σ 3 at 124°/07°, 213°/04°, and 001°/75°, respectively. These results, combined with geochronological analysis, indicate two episodes of shortening in this belt during the Mesozoic. Late Triassic–Early Jurassic NNE–SSW shortening, which produced ∼8.1 km of horizontal shortening, led to the development of open WNW-trending fold structures. Subsequent Late Jurassic–Early Cretaceous WNW–ESE shortening, which produced ∼18.7 km of horizontal shortening, reshaped the early WNW-trending structures and generated close, overprinting NNE-trending folds that resulted in the development of the regional-scale superposed folds in this area. In terms of geodynamics, the early NNE–SSW shortening is likely to be related to Indosinian intercontinental convergence between the North China Plate and the Yangtze Plate, and the later WNW–ESE shortening is likely to have been related to subduction of the Paleo-Pacific Plate. The regional structural analysis indicates that the whole of the western North China Plate experienced two-phase contractional deformation during the Mesozoic, as manifest by the early NNE–SSW and the late WNW–ESE shortening that characterized Mesozoic intracontinental deformation in the western NCP. [ABSTRACT FROM AUTHOR]

The Shanxi Rift, an intracontinental belt along the eastern margin of the Ordos Block, North China Plate, has undergone multi-stage extensional deformation during the late Cenozoic. In this study, new fault kinematic analysis of boundary faults in the Shanxi Rift, constrained by geochronological data, defines a three-stage tectonic stress regime since the late Miocene, providing new structural evidence for deciphering the northeastward growth of the Tibetan Plateau. The earliest stage involved a transtensional stress regime of NW–SE extension and NE–SW compression in the late Miocene–early Pleistocene (ca. 10–1.8 Ma) and characterized by mean principal stress axes of σ 1 at 344.7°/87.2°, σ 2 at 217.6°/01.1°, and σ 3 at 128.1°/01.0°. The early transtensional stress regime was responsible for the opening of the Shanxi Rift and was very likely associated with intensive right-lateral pull-apart activity in the eastern Ordos Block due to the northeastward growth of the Tibetan Plateau. During the second stage, the stress regime changed to less intense NE–SW extension, with mean stress orientations of 323.3°/85.2° for σ 1 , 127.5°/02.9° for σ 2 , and 214.9°/02.6° for σ 3 in the early late Pleistocene (ca. 1.8–0.11 Ma). This stage is marked by a distinct shift from fluvio-lacustrine to fluvio-piedmont sedimentary facies at the end of the early Pleistocene, and the widespread eruption of basalt in the Datong Basin north of the Shanxi Rift. This short-lived extension appears to be the result of relaxation in the midst of crustal shortening during growth of the Tibetan Plateau. The third stage was transtensional, characterized by NNW–SSE extension and WNW–ESE compression ( σ 1 at 060°/88.9°, σ 2 at 074.9°/03.9°, and σ 3 at 164°/00°) since the late Pleistocene (ca. 0.11 Ma), causing dextral shear deformation in the Shanxi Rift and the disappearance of its paleo-lake. This stage resulted from regional ENE–WSW shortening due to northeastward growth of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Abstract: The Xianshuihe–Xiaojiang fault zone (XFZ) forms a prominent linear NW–SE trending tectonic feature along the southeastern margin of the Tibetan Plateau. The spatial and temporal evolution of the predominantly strike–slip movement along the fault remains unclear, as estimates for the initiation age of its different segments range from 5 to 13Ma. The Jinhe–Qinghe fault (JqF; the south part of the Longmen Shan thrust belt) provides a key for understanding the tectonic role and deformation history of the Xianshuihe–Xiaojiang fault zone in terms of timing, magnitude of displacement, and spatial–temporal evolution. This paper presents research on the structure and chronology of the JqF. The results of a geometric and kinematic study of the Jinhe–Qinghe fault show it to be a thrust fault with a left-lateral strike slip component; The strike slip offset extends at least 13–18km to southwest, based on the shortening of its folds and faulting, and based on stream deflection. Ten apatite fission track apparent ages show a pronounced change in age/elevation gradient at ~17±2Ma, consistent with an abrupt increase of exhumation due to uplift of the hanging wall of the JqF at that time. Combined with the age of deformed Tertiary strata in the footwall of the JqF and the geometric relationships of the JqF with the Chenghai fault and the XFZ, this indicates that the JqF was active between 17 and 5Ma. Based on the fault chronology, geometry, and movement, we suggest that the fault was a transpressional structure at the south end of the XFZ during the period from 17 to 5Ma. [Copyright &y& Elsevier]

Abstract: Determining the slip-rate history along the right-lateral Karakorum fault (KF) is fundamental to understanding its present-day kinematic role in the deformation of Tibet. Geodetic and geologic studies suggest slip-rates of 0–11mm/yr along this structure. Whether slip-rate variability exists along strike and/or time, or simply results from different measuring techniques/timescales, remains unknown. In order to constrain slip-rates within a timescale of 200ka, we studied fluvial and glacial geomorphic features that are right-laterally or vertically offset by the fault by varying amounts from 7±1m to 430±30m and up to 53±5m, respectively. We constrained their ages using 10Be surface exposure dating on 141 quartz-rich samples collected on 4 lateral moraines and at 3 alluvial sites along the southernmost segment of the KF (Menshi–Kailas basin) and along the Gurla Mandhata detachment fault in the Pulan graben. From the 30° fault bend at Baer (80.5°E) to Mount Kailas area, the slip-rate along the KF is >7.1+3.2/−1.7 mm/yr at Menshi and >7.9+3.2/−2.5 mm/yr at Kailas (slip on two parallel fault strands). In the Pulan graben, the normal fault slip-rate is >1.6+0.4/−0.3 mm/yr. Our data suggest that the Quaternary slip-rate along the southern KF does not decrease eastward but is constant along strike for at least 200km, from >5–11mm/yr in the Gar basin further north to >7–8mm/yr in the Menshi–Kailas basin. Because no expected along-strike slip-rate gradient is observed, it implies that the KF does not end at the Kailas but must extend where the slip rate decreases, i.e. eastward along the Yarlung Zangbo suture and southward along the Gurla Mandhata–Humla fault system. [Copyright &y& Elsevier]

Abstract: Determining the relationship between deformation and exhumation history in the footwall rocks of major low-angle normal faults (i.e., detachment faults) provides a way to quantify different models of continental extension. Although pressure–temperature–time (P–T–t) datasets are commonly used to infer magnitude and rates of slip across detachment faults, correct use of these datasets requires a sound understanding of coupling effects between footwall deformation and advection of isotherms on the distribution of cooling ages. In this study we present thermo-kinematic modeling results which examine the relationship between different footwall kinematic models, erosion, and the spatial distribution of muscovite and biotite 40Ar/39Ar cooling ages. Our results show that large magnitudes of footwall erosion during normal faulting significantly affect cooling age patterns as footwall rocks at different distances from the fault surface pass through different thermal gradients. We apply our modeling results to simulating muscovite and biotite cooling-age patterns from the footwall of the Cenozoic Kongur Shan normal fault system in the Pamir. Previous studies had interpreted a documented ~5-fold increase in cooling rate at ~2Ma to indicate an increase in exhumation rate during the Quaternary. However, our results show that the observed cooling age patterns and increase in cooling rate can be produced by a constant exhumation rate over the last 7Ma due to the effect of changes in the rate of isotherm advection during exhumation. [ABSTRACT FROM AUTHOR]

Structural style along the active, NW-striking, right-slip Karakoram fault in western Tibet ranges from transpression in the north (37° to 34°N) to transtension in the south (34° to 32°N). This transition in structural style occurs at a 27-km-wide bend in the fault. Our new neotectonic mapping has documented the long-asserted structural linkage between the ENE-striking Gozha–Longmu Co fault system and the similarly oriented active, leftslip Altyn Tagh fault to the northeast. This mapping also indicated that the restraining bend in the Karakoram fault is located where this fault intersects the Gozha-Longmu Co extension of the Altyn Tagh fault to the west. Additional observations from remotely sensed imagery suggest that the total left-separation along the Gozha-Longmu Co fault system is 25-32 km. We use the new neotectonic mapping and published slip rates to develop a simple kinematic model for the main active faults in western Tibet to explore the genetic relationship between slip along the Gozha- Longmu Co fault system and the geometric and kinematic evolution of the Karakoram fault. This model combines published geodetic and Quaternary slip rates with the known fault geometries and demonstrates that the transition from transpression to transtension along the Karakoram fault can be explained by differential motions between the NW Himalaya, the Tianshuihai terrane, and the Tibetan Plateau. These motions produce bending and transtension along the central and southern Karakoram, respectively, and movement of the Tibetan Plateau at a rate of 6–13 mm/ yr toward the east-southeast relative to the Pamirs. We also fi nd that the Gozha–Longmu Co fault system likely initiated between 10 and 3 Ma to accumulate 25–32 km of total left separation. We suggest that the Gozha-Longmu Co fault system formed during late Miocene to Pliocene structural reorganization of the southwestern Altyn Tagh and southern Karakoram fault systems to allow eastward migration of the Tibetan Plateau and northward migration of the Pamir syntaxis. [ABSTRACT FROM AUTHOR]

The collision of the Indian subcontinent with Asia drives the growth and evolution of the greater Tibetan Plateau region. Fault slip rates resulting from the relative motion between crustal blocks can provide a kinematic description of the distribution of present-day deformation. I construct a three-dimensional, regional-scale elastic block model of the India-Asia collision zone that is consistent with geodetic observations of interseismic deformation, mapped fault system geometry, historical seismicity, and the mechanics of the earthquake cycle. This mechanical model of the elastic upper crust yields a set of kinematically consistent fault slip rates and block motions that may serve to constrain dynamic models of continental crustal dynamics. [ABSTRACT FROM AUTHOR]