The northeastern Tibetan Plateau constitutes a transitional region between the low-relief physiographic plateau to the south and the high-relief ranges of the Qilian Shan to the north. Cenozoic deformation across this margin of the plateau is associated with localized growth of fault-cored mountain ranges and associated basins. Herein, we combine detailed structural analysis of the geometry of range-bounding faults and deformation of foreland basin strata with geomorphic and exhumational records of erosion in hanging-wall ranges in order to investigate the magnitude, timing, and style of deformation along the two primary fault systems, the Qinghai Nan Shan and the Gonghe Nan Shan. Structural mapping shows that both ranges have developed above imbricate fans of listric thrust faults, which sole into décollements in the middle crust. Restoration of shortening along balanced cross sections suggests a minimum of 0.8–2.2 km and 5.1–6.9 km of shortening, respectively. Growth strata in the associated foreland basin record the onset of deformation on the two fault systems at ca. 6–10 Ma and ca. 7–10 Ma, respectively, and thus our analysis suggests late Cenozoic shortening rates of 0.2 +0.2/–0.1 km/m.y. and 0.7 +0.3/–0.2 km/m.y. along the north and south sides of Gonghe Basin. Along the Qinghai Nan Shan, these rates are similar to late Pleistocene slip rates of ∼0.10 ± 0.04 mm/yr, derived from restoration and dating of a deformed alluvial-fan surface. Collectively, our results imply that deformation along both flanks of the doubly vergent Qilian Shan–Nan Shan initiated by ca. 10 Ma and that subsequent shortening has been relatively steady since that time.
Abstract In this study, channel steepness and main divide migration analysis were conducted on the Qinghai Nanshan to confirm the activity and evolution of the range. The results showed that the broad and gently dipping northern limbs correspond to relatively low steepness values, while the narrow and steeply dipping southern limbs are characterized by higher steepness distribution. In addition, main divide of the range is currently stable, despite its tendency migrating northward. Based on previous numerical simulations and our geomorphological results, we suggested that the Qinghai Nanshan thrust Fault is tectonically active. The sustained thrust activities of the fault have uplifted the Qinghai Nanshan, driven southward migration of the main divide and caused obvious regional crustal shortening and thickening. Given the same landscape characteristics as the Qinghai Nanshan, the Gonghe Nanshan was found to have appreciable influence on regional crust deformation. Secondary active tectonics (e.g. the Qinghai Nanshan and Gonghe Nanshan) could subdivide rigid blocks into smaller ones and promote the slip transferring and strain regulation between boundary strike‐slip faults. In summary, we concluded that continuous crustal deformation within the northeastern Qinghai‐Tibet Plateau is implemented through strain assimilation by minor faults in minor blocks.
On 8 January 2022, a seismic event of significant magnitude (Mw 6.7, Ms 6.9) occurred in the northeastern region of the Tibetan Plateau. This earthquake was characterized by left-lateral strike-slip motion, accompanied by a minor reverse movement. The Menyuan earthquake resulted in the formation of two main ruptures and one secondary rupture. These ruptures were marked by a left-lateral step zone that extended over a distance of 1 km between the main ruptures. The length of the rupture zones was approximately 37 km. The surface rupture zone exhibited various features, including left-lateral offset small gullies, riverbeds, wire fences, road subgrades, mole tracks, cracks, and scarps. Through a comprehensive field investigation and precise measurement using unmanned aerial vehicle (UAV) imagery, 111 coseismic horizontal offsets were determined, with the maximum offset recorded at 2.6 ± 0.3 m. The analysis of aftershocks and the findings from the field investigation led to the conclusion that the earthquake was triggered by the Lenglongling fault and the Tuolaishan fault. These faults intersected at a release double-curved structure, commonly referred to as a stepover. During this particular process, the Lenglongling fault was responsible for initiating the coseismic rupture of the Sunan–Qilian fault. It is important to note that the stress applied to the Tuolaishan fault has not been fully relieved, indicating the presence of potential future hazards.
[1] Based on field investigations, aerial-photo morphological analysis, topographic profiling, and optically stimulated luminescence (OSL) dating of alluvial surfaces, we estimate vertical components of the slip rate along the South Heli Shan thrust fault, which lies on the northern margin of the Hexi Corridor and the northeastern edge of the Tibetan Plateau. The fault consists of three segments with scarp heights ranging from less than 1 m to more than 16 m. OSL dating indicates that most of the alluvial fans cut by fault scarps formed during the transition from the last glacial stage to the present interglacial stage from ~19 to ~9 ka along southern Heli Shan and from ~27 ka to ~22 ka along its northern margin. In addition, remnants of older alluvial fan have been abandoned after ~67 ka. Scarp heights increase from west to east and reach a maximum of more than 16 m near the eastern end. Using three approaches, we calculate late Quaternary slip rates for each of the three fault segments along the southern margin and the fault on the northern flank. These approaches yield maximum vertical slip rates from 0.18 to 0.2 mm/a for the western segment, 0.3 to 0.43 mm/a for the central segment, 0.36 to 0.53 mm/a for the eastern segment, and 0.21 mm/a for the Wutongjing Fault, which lies on the north side of the Heli Shan. For a range of likely fault dips, these correspond to 0.1–0.2 mm/a of average horizontal shortening for the western segment, and increase to 0.4–0.5 mm/a across the eastern segment of the southern Heli Shan Fault. Combining the height of the eastern parts of the Heli Shan (Daqing Peak) above the Hei He (a major river that incised the western end of the range) and the vertical component of the slip rate of the eastern segment, we suggest that the Heli Shan was uplifted by motion on the South Heli Shan Fault beginning sometime between 1 and 4 Ma, most likely since ~2 Ma. This age suggests that the Tibetan Plateau continues to grow northeastward across the Hexi Corridor.
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.
Abstract Altyn Tagh fault controls the deformation characteristics of the northern margin of the Qinghai‐Tibet Plateau. The sinistral slip rate of the eastern segment of the fault reduces gradually where the reduction transforms into the deformation within Qilian Mountain, forming a series of thrust faults and strike‐slip faults. Among them, the Yema River‐Daxue Mountain fault is one of the important structural transform faults in the study area. Based on the differences of the geometrical characteristics and activities, the fault is divided into four segments, the Yema River segment, the Shibandun segment, the Liushapo segment and the Baishitougou segment, among which the former three are Holocene active faults, and the Baishitougou segment belongs to late Pleistocene fault. The excavated trenches imply a total of 6 paleoearthquake events, and at least 4 events have occurred during Holocene, whose occurrence times are 8300±700 yr BP, 6605±140 yr BP, 4540±350 yr BP, 2098±47 yr BP, respectively. The recurrence interval is 2600±600 yr BP that is close to the lapsed time of the last one, 2098±47 yr BP, which suggests that the Yema River‐Daxue Mountain fault is in a high risk of major earthquakes in the future. The vertical coseismic displacements of the four Holocene paleoearthquake events are 100 cm, 42 cm, 40 cm and 50 cm, respectively, the horizontal coseismic displacements are 5 m, 4.5–5.5 m, 5–8 m and 4–5.5 m, separately, and then the reference magnitude of the paleoearthquake events is conjectured to be M7.6±0.1.
Research Article| March 01, 2007 Signatures of mountain building: Detrital zircon U/Pb ages from northeastern Tibet Richard O. Lease; Richard O. Lease 1Department of Earth Science, University of California-Santa Barbara, California 93106, USA Search for other works by this author on: GSW Google Scholar Douglas W. Burbank; Douglas W. Burbank 1Department of Earth Science, University of California-Santa Barbara, California 93106, USA Search for other works by this author on: GSW Google Scholar George E. Gehrels; George E. Gehrels 2Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar Zhicai Wang; Zhicai Wang 3State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Daoyang Yuan Daoyang Yuan 3State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Geology (2007) 35 (3): 239–242. https://doi.org/10.1130/G23057A.1 Article history received: 02 Jun 2006 rev-recd: 26 Oct 2006 accepted: 27 Oct 2006 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Richard O. Lease, Douglas W. Burbank, George E. Gehrels, Zhicai Wang, Daoyang Yuan; Signatures of mountain building: Detrital zircon U/Pb ages from northeastern Tibet. Geology 2007;; 35 (3): 239–242. doi: https://doi.org/10.1130/G23057A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract 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. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
