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The Qilian Mountains are situated on the northeastern margin of the Tibetan Plateau and serve as the leading edge of the plateau's northeastward expansion. The Menyuan Basin, characterized by typical basin landforms, provides valuable insights into the region's neotectonic activity and geomorphic evolution. As a representative mountain basin located in the central part of the Qilian Mountains, the Menyuan Basin's development pattern and geomorphic features are closely linked to tectonic activity. This study aims to investigate the variations in tectonic activity and their underlying causes along the north margin fault and different zones of the Menyuan Basin. To achieve this, 30 m resolution digital elevation model (DEM) data and ArcGIS spatial analysis technology were employed to extract the hypsometric integral (HI) and hypsometric integral curve (HC) of 15 rivers that traverse the northern edge of the basin. Subsequently, kriging interpolation was utilized to obtain the spatial distribution characteristics of HI within the basin. The findings reveal that HI values generally exhibit higher values on the western side and lower values on the eastern side of the Menyuan Basin, with the turning point (Laohugou) of the northern fault at the Menyuan Basin serving as the boundary. By combining the distribution of HI with field investigation results of active structures, it is observed that the eastern fault has extended into the basin's interior, giving rise to a series of active reverse fault–fold zones. This phenomenon may be attributed to changes in fault trends and the presence of northeastward faults. Additionally, a high HI anomaly is detected near Qingshizui Town in the basin's interior. Based on previous electromagnetic detection results, it is inferred that a buried fault exists within the basin. Furthermore, the study demonstrates that most rivers exhibit peak fluctuations in the stream length–gradient index (SL) at a specific position upstream of the main fault, indicating a strong correlation between the location of SL fluctuations and the position of the fault intersecting the river. In other words, tectonic activity can exert a significant influence on SL. Abnormal fluctuations near lithological transitions may suggest that local changes in lithology also impact the stream length-gradient index. The comprehensive analysis underscores the substantial differences in geomorphic development between the eastern and western sections of the northern edge of the Menyuan Basin, primarily controlled and influenced by the active structures in this region. Moreover, the aforementioned geomorphic parameters serve as sensitive indicators for evaluating tectonic activity.

The West Qinling Belt (WQB) situated in the central China continent, is an enormous structure on the crustal scale, which is not controlled only by the Tethyan tectonic domain but is more complex, involving additional tectonic domains. The composite WQB as the coordinate system, which underwent five major episodes of accretion and collision between discrete continental blocks, has distinct geological and geophysical structure, geomorphology and environment, characterized by complex structures, complex forming processes and mixed materials. Moderate-strong earthquakes occurred frequently in the WQB in recent years, attesting its tectonic activity. Numerous results from the studies related to active fault geological and geodesic observations gave us new insights into present-day crustal deformation characteristics and its dynamic mechanism and helped us in exploring the control effect of active tectonic system on significant earthquake events in the WQB. Two groups of faults striking in different direction (NWW-trending and NEE-trending) within the WQB have played significant roles in the tectonic deformation and the transference slip along the east end of the east Kunlun fault since the Quaternary. Recent results suggest that the < 2 mm/a slip rate at the tip of the east Kunlun fault is absorbed by low slip rate faults, crustal shortening, basin formation, mountain uplift and block rotation in the WQB. Whereas deformation in the shallow brittle crust does not occur on a major fault, deformation of a continuous medium at depth best describes the present-day tectonics of the WQB. Regionally, mantle magmatism, geophysical and geological data show that the actively deforming WQB crust is dominated by main mountain building contraction shortening strain in the upper crust, decoupled plastic deformation in the lower crust and extrusion of the mantle lithosphere below to the high-strain domains in the crust above, and such a transition zone (high and low velocity/resistivity anomalies) is relatively easy to accumulate stress, leading to occurrence of major earthquake in this area.

Two of the most popular mechanisms for thickening the crust beneath the Tibetan Plateau are (1) pure shear with faulting and folding in the upper crust and horizontal shortening below and (2) flow of lower or middle crust without significant shortening of the upper crust. To help discriminate between the relative contributions of these two mechanisms, well-constrained estimates of upper crustal shortening are needed. Here we document the Cenozoic shortening budget across the northeastern Tibetan Plateau margin with several balanced cross sections that exploit thermochronological and magnetostratigraphic constraints. These sections indicate 11 +2/-1% east-west shortening since middle Miocene time and ∼9 +2/-3% NNE-SSW shortening between middle Eocene and middle Miocene times with little subsequent shortening of this orientation. Shortening rates accelerate fivefold after middle Miocene time. Given the present-day crustal thickness of 56 4 km in northeastern Tibet, crustal restorations that remove Cenozoic shortening suggest that the northeastern Tibetan crust was 45±5 km thick prior to the India-Asia continental collision. This precollision thickness estimate is equivalent to average continental crustal thicknesses both adjacent to the Tibetan Plateau (44±4 km) and globally (41±6 km) and suggests that pure shear alone may account for Cenozoic crustal thickening in northeastern Tibet. In contrast to eastern Tibet where, in the absence of significant shortening structures, crustal flow has been invoked to explain the addition of crustal material since middle Miocene time, our results may obviate lower crustal flow as a necessary crustal thickening agent in northeastern Tibet. Copyright © 2012 by the American Geophysical Union.

Sedimentary rocks in Tibetan Plateau basins archive the spatiotemporal patterns of deformation, erosion, and associated climate change that resulted from Cenozoic continental collision. Despite growing understanding of basin development in northeastern Tibet during initial India-Asia collision, as well as in the late Miocene-Holocene, surprisingly little is known about the intervening period: a time when the plateau may have undergone fundamental tectonic changes. To fill this gap, we present new magnetostratigraphy from a >2300-m-thick fluviolacustrine succession that spans ca. 30-9.3 Ma. An integrated analysis of sedimentology, subsidence, and provenance from this section reveals the sequential, pulsed erosion of multiple ranges bordering the Xunhua Basin. Emergence of the WNW-trending Laji Shan is highlighted by a doubling of sediment accumulation rates between 24 and 21 Ma and a transition to coarse allu vial facies at 20.3 Ma. Detrital zircon U/Pb age spectra show that these coarse sediments came from basement terranes within the Laji Shan. Together these observations suggest accelerated growth of the Laji Shan and its coupled foreland basin at ca. 22 Ma. The most rapid accumulation rates in Xunhua Basin occur within the finest-grained strata and suggest an underfilled basin during the fastest interval of Laji Shan deformation. Growth of the Laji Shan occurred northward of the contemporaneous plateau margin, which had been defined since ca. 45-50 Ma by the West Qinling, lying ~60 km farther south. Hence, following ~20-25 m.y. of apparent stability, the deformation front in this region jumped ~60 km to the north at ca. 22 Ma. Subsequently, growth of the north-trending Jishi Shan occurred at ca. 13 Ma and is highlighted by an acceleration in Xunhua Basin accumulation rates between 12 and 9 Ma, as well as by a significant change in detrital zircon provenance of nearby Linxia Basin deposits by 11.5 Ma. Initial growth of the WNW-trending Laji Shan in the early Miocene and subsequent growth of the north-trending Jishi Shan ~10 m.y. later support interpretations of a middle Mio cene kinematic reorganization in northeastern Tibet. © 2012 Geological Society of America.

Understanding the three‐dimensional structure, segmentation, and kinematics of complex fault systems is essential to assessing the size of potential earthquakes and related seismic hazards. The Danghe Nan Shan thrust, a major splay of the Altyn Tagh fault (ATF) in north Tibet, is one of these complex fault junctions. Near the town of Subei, the western Danghe Nan Shan thrust composes two left‐stepping faults outlined by fault scarps in front of folded and uplifted alluvial fans and terraces. Age constraints and 2D reconstructions of the accumulated slip above a transient base level of four terraces standing 7–60 m above the present stream bed yield shortening and vertical uplift rates of 0.5 ± 0.1 and 1.1 ± 0.3 mm/yr, respectively, over the last 130 ka on the southern thrust. Along the northern thrust, vertical terrace offsets of 1.5–3.6 m and horizontal slip of 4.5 m documented in a paleoseismological trench occurred after 12 ± 4 ka, constraining coeval rates of 0.3 ± 0.1 mm/yr for uplift and shortening. Overall, 1.4 ± 0.4 mm/yr terrace uplift and 0.8 ± 0.2 mm/yr shortening rates are determined, in agreement with late Miocene long‐term exhumation rate estimates. Our fault mapping and geomorphic and structural observations imply that the western Danghe Nan Shan thrust accommodates slip transfer from the ATF to the west to thrusting and shortening farther east in the Qilian Shan region. Considering the scarp sizes, their lateral extent, the geometry of the faults at depth, and their slip‐rate, we suggest the possible occurrence of Mw 7+ earthquakes near Subei. Plain Language Summary: How faults slip is essential to understanding continental deformation and seismic hazards. In the western Qilian Shan region, the Danghe Nan Shan is one of the largest ranges bounded by active thrust faults. West and south of Subei, these thrusts can be followed for several kilometers along meter‐high scarps and folded terraces. Quantifying the cumulative deformation of the folded and uplifted terraces and fans enables to constrain shortening rates of about 1 mm/yr over the last 130 ka. Evidence from surface geomorphology and sub‐surface trenching across the faults indicates the occurrence of large magnitude potentially up to Mw 7 seismic events in the last 16 ka. Integrating age‐controlled cumulative geological observations with field‐documented co‐seismic deformation increases the knowledge of slip rate and co‐seismic displacement for seismic hazards. Key Points: Combined cosmogenic nuclides, optically stimulated luminescence, and 14C dating methods constrain the deposition age of four folded inset terraces over the last 130 kaThe shortening rate of 0.8 ± 0.2 mm/yr across the western Danghe Nan Shan thrusts is coeval with decreasing left‐slip along the Altyn Tagh faultConcurrent rupture of thrusts and strike‐slip fault strands could result in a Mw 7+ earthquake southwest of Subei town [ABSTRACT FROM AUTHOR]

Although detrital zircon has proven to be a powerful tool for determining provenance, past work has focused primarily on delimiting regional source terranes. Here we explore the limits of spatial resolution and stratigraphic sensitivity of detrital zircon in ascertaining provenance, and we demonstrate its ability to detect source changes for terranes separated by only a few tens of kilometers. For such an analysis to succeed for a given mountain, discrete intrarange source terranes must have unique U/Pb zircon age signatures and sediments eroded from the range must have well-defined depositional ages. Here we use ~1400 single-grain U/Pb zircon ages from northeastern Tibet to identify and analyze an area that satisfies these conditions. This analysis shows that the edges of intermontane basins are stratigraphically sensitive to discrete, punctuated changes in local source terranes. By tracking eroding rock units chronologically through the stratigraphic record, this sensitivity permits the detection of the differential rock uplift and progressive erosion that began ca. 8 Ma in the Laji Shan, a 10-25-km-wide range in northeastern Tibet with a unique U/Pb age signature. Keywords: detrital zircon, Tibet, provenance, unroofing, Miocene, U/Pb.