Altyn Tagh Fault System Research Articles

The seismicity in the middle section of the Altyn Tagh Fault system revealed by a dense nodal seismic array

The left-lateral Altyn Tagh Fault (ATF) system is the northern boundary of the Qinghai-Xizang Plateau, separating the Tarim Basin and the Qaidam Basin. The middle section of ATF has not recorded any large earthquakes since 1598 AD, so the potential seismic hazard is unclear. We develope an earthquake catalog using continuous waveform data recorded by the Tarim-Altyn-Qaidam dense nodal seismic array from September 17 to November 23, 2021 in the middle section of ATF. With the machine learning-based picker, phase association, location, match and locate workflow, we detecte 233 earthquakes with ML -1-3, far more than 6 earthquakes in the routine catalog. Combining with focal mechanism solutions and the local fault structure, we find that seismic events are clustered along the ATF with strike-slip focal mechanisms and on the southern secondary faults with thrusting focal mechanisms. This overall seismic activity in the middle section of the ATF might be due to the northeastward transpressional motion of the Qinghai-Xizang Plateau block at the western margin of the Qaidam Basin.

Jurassic sedimentary migration characteristics and their geodynamic implications in the Dunhuang Basin and adjacent regions, Northwestern China

The Dunhuang Basin, situated in western China along the Altyn Tagh Fault (ATF) zone, intersects the Tethys and Paleo‐Asian Ocean tectonic domains. Influenced by both the ATF system and the far‐field effects of the Qiangtang‐Lhasa‐Eurasia collision during the Mesozoic, the mechanism of the Jurassic sedimentary migration of the basin in response to tectonic movements is unclear so far. The paper uses a comprehensive approach, including field geological surveys, lithologic and lithofacies discern, stratigraphic relationships analysis and 2D seismic profile interpretation, to examine the distribution of Jurassic residual strata in the basin. The comprehensive results of our study suggest that the Dunhuang Basin exists as an isolated block with unique tectonic and sedimentary evolution characteristics. In the Early Jurassic, the Dunhuang Basin underwent initial rifting, leading to the formation of small segmented intermontane sags. This phase was marked by the coarse particle sedimentary system of alluvial fans and braided rivers, represented the near source rapid deposition in the initial formation period of the basin. Stratigraphic distribution was primarily influenced by pre‐Jurassic basement topography and was not significantly constrained by faulting during this period. The formation of these isolated discontinuous small intermontane sags indicates the segmented activities of the ATF in the Early Jurassic period. In the Middle Jurassic period, influenced by the ATF dextral strike‐slip faulting, sedimentation extended eastward and the depocenter migrated clockwise compared with the distribution of the Middle Jurassic strata within the Dunhuang Basin. This period witnessed the development of coal measure strata at the basin's margins and lacustrine fine‐grained clastic deposition in the centre. The segmented fracture of the ATF gradually initiated a unified dextral strike‐slip tectonic movement. In the Late Jurassic period, sedimentary strata were locally present in the Wanyao Sag but absent in other sags. The depocenter migrated counterclockwise compared with the distribution of Middle Jurassic strata within the Dunhuang Basin, due to regional uplift accompanied by the ATF sinistral strike‐slip faulting caused by the collision between the Lhasa Block and the Eurasia Plate. The depocenter migration of the Dunhuang Basin constrained within the ATF system from the Early to Middle and Late Jurassic can be attributed to the transition of the ATF strike‐slip faulting in context of the stress relaxation and compression between the collision of the Qiangtang and Lhasa blocks to the Eurasia Plate, respectively.

Underthrusting of Tarim Lower Crust Beneath the Tibetan Plateau Revealed by Receiver Function Imaging

AbstractThe left‐lateral Altyn Tagh Fault (ATF) system is the northern boundary of the Tibetan Plateau resulted from the India–Eurasia continental collision. How intracontinental deformation across the central ATF responds to the distal collision remains elusive, primarily due to unclear crustal structure. We obtained detailed crustal structure across the central ATF using receiver functions recorded by ∼NW–SE oriented linear dense array. The images reveal the Tarim lower crust is underthrusting beneath the Tibetan Plateau and reaches to a maximum depth of ∼75 km and undergoing partial eclogitization. The two south‐dipping interfaces imaged beneath the Altyn Tagh Range (ATR) represent the thrusting Northern Altyn Fault and its branch fault. Oblique convergent forces extruded upper crustal materials along the thrust faults, creating the pop‐up structure of ATR, supported by low Vp/Vs ratios. Our balanced cross‐section for the Moho suggests intracontinental deformation in the ATR has accelerated since the late Miocene.

Two-Stage Evolution of the Altyn Tagh Fault System during the Tertiary: Constraints from Heavy Mineral Chemistry in Sediments of the Northwestern Qaidam Basin, Western China

The tectonic evolution of the Altyn Tagh Fault (ATF) remains controversial during the Tertiary. Qaidam Basin is the largest and highest plateau inland basin inside the Tibet Plateau. Sediments in the basin provide sedimentary records of the evolution history of its surrounding orogens, such as the ATF, located on the northwest margin of the Qaidam Basin. Comprehensive analyses of sandstone petrography, heavy mineral assemblages, and mineral geochemistry were adopted to effectively indicate the tectonic evolution history of ATF. The result indicates that the sediments in a wide range of the northwestern Qaidam Basin (e.g., the Xichagou section, the Yueyashan section) were derived from the Altyn Mountains. The increasing immaturity of sediments, increased denudation, and sedimentation processes from the early-middle Miocene to the Pliocene can be explained by the active tectonic setting of the ATF. During the early Miocene (ca. 22 Ma), there was an abrupt change in the heavy mineral composition of sediments in the northwestern Qaidam Basin. This change may be attributed to the large-scale slip motion along the ATF. Therefore, ~22 Ma is the key transforming period of the ATF system. On the foundation of the above, we suggest a two-stage evolution model of the ATF during the Tertiary: (1) From the late Eocene to the Oligocene, the tectonic setting of the ATF was relatively calm; (2) During the early Miocene period, the ATF underwent large-scale tectonic activation. It is likely to be a strike-slip tectonic activity, accompanied by an uplift of the Altyn Mountains. The active tectonic setting of the ATF was sustained after the Miocene.

An Evolving Lithospheric‐Scale Wrench Fault System Along the Eastern End of the Altyn Tagh Fault: Kinematics and Quaternary Activity of the Heishan Fault System, Western China

AbstractThe Altyn Tagh fault (ATF) is a major intracontinental strike‐slip fault system that defines the northern margin of the Tibetan Plateau. The fault system loses its obvious surface expression north of the Qilian Shan fold‐and‐thrust belt, but may link eastward with multiple faults in the northern Hexi Corridor and southern Alxa block. To better understand the potential connectivity and displacement transfer between the ATF and the northern Hexi Corridor fault array, we carried out a multidisciplinary field and remote sensing‐based investigation of the actively deforming Heishan and Jinta'Nanshan region north of Jiayuguan City. We document Quaternary sinistral strike‐slip motion on the Heishan fault (HF) system and active sinistral transpression within a 70‐km‐long, E‐W deforming belt east of the Heishan, which is characterized by multiple left‐stepping, en‐échelon Quaternary folds and linking faults. Cosmogenic10Be dating of displaced terrace surfaces yields a vertical slip rate of ∼0.2 mm/a for the northern Heishan thrust and a sinistral strike‐slip rate of 0.6 ± 0.2 mm/a for the HF. Within the uplifted core of the Heishan massif, the HF contains ductilely deformed Paleozoic basement lithologies with dextral‐sense shear fabrics that indicate that the modern HF has reactivated and inverted an older shear zone. A previously published magnetotelluric profile across the HF system suggests that it roots into a steep, deeply penetrating fault that is unlinked to the Qilian Shan thrust wedge. Instead, we suggest that the active sinistral deformation belt of the Heishan‐Jinta'Nanshan represents the eastward‐evolving, upper crustal expression of the modern ATF system.

From Left Slip to Transpression: Cenozoic Tectonic Evolution of the North Altyn Fault, NW Margin of the Tibetan Plateau

AbstractThe Cenozoic North Altyn Fault (NAF) is a major splay of the Altyn Tagh Fault along the northwestern margin of the Tibetan Plateau, but its role in the development of this plateau margin in response to the India‐Eurasia collision is highly debated. Here, we investigate fault geometry, kinematics, and shortening magnitude along the westernmost 120 km of the NAF. Seismic surveys reveal minimal Cenozoic shortening in the subsurface of the Southeast Tarim Basin and support for large‐scale (>120 km) left slip on the NAF. Based on the satellite imagery, two new faults are identified to define the northern boundary of the NAF system, which together with the NAF to the south constitute a narrow transpressional shear zone comprised of three basement‐cored, fault‐bound slivers. Fission track data and thermal modeling indicate that the NAF zone experienced broad reburial during early Cenozoic that was locally interrupted by ∼40 to 35 Ma exhumation proximal to the NAF, followed by widespread but heterogeneous exhumation since ∼17 to 15 Ma associated with ∼9 to 11 km of total shortening across the NAF system via thick‐skinned faulting. We conclude that the NAF initiated as a left‐slip fault at ∼40 to 35 Ma and then became transpressional at ∼17 to 15 Ma during the middle‐Miocene reorganization of the Altyn Tagh Fault system. We find no evidence to support prior inferences of large‐scale (∼100 km) underthrusting of the Tarim Basin beneath the Tibetan Plateau along the NAF.

Drainage Development in the Dunhuang Basin, NE Tibet, Controlled by Multi-Segment Fault Growth

The Dongbatu Shan (DBTS, also known as the Nanjie Shan), which interrupts the northern Tibetan foreland in the Dunhuang basin, is an active anticline. It has accommodated the northwestern growth of the eastern Altyn Tagh fault system (ATF). Although several thrust faults have been identified around the DBTS, their evolution history and influence on regional landscape have received little attention during the late-Quaternary. In this study, several geomorphic methods are used to investigate the interaction between drainage development and tectonic movement around DBTS. Based on high-resolution satellite images, field investigation, and cosmogenic nuclide 10Be dating method, the fluvial landform sequences around DBTS were constructed. Using quantitative geomorphology methods including landscape relief profile, asymmetry factor (AF), and transverse topographic symmetry factor (T), we hypothesize that drainage deflection is controlled by multi-segment fault growth. Combining the results of the above-mentioned methods, we propose that Yulin He, flowing across the DBTS, had gone through several abandonments since the late mid-Pleistocene due to the lateral propagation of DBTS. Affected by the discharge of channel and multi-segment fault growth, our research confirms that the direction of river abandonment may have decoupled with the mountain range propagation trend. Based on the chronology dating, the DBTS has gone through two severe uplifts since ∼208 ka and the shortening rate across the central DBTS is constrained to be ∼1.47 mm/yr since ∼83 ka. Given the fact that thrust faults are widely developed around DBTS, we propose that the flower-like structure formed by the northward growth of the eastern ATF could better explain the development of the secondary subparallel faults.

Middle Miocene climate transition in the Tibetan Plateau: identification and significance

AbstractThe Middle Miocene Climatic Optimum is known for abrupt events during the global cooling trend of the past 20 Ma. Its identification in the Tibetan Plateau can help explain the cause of the critical Middle Miocene climate transition in Central Asia. In this study, fine-grained mixed sediments widely distributed in the Miocene Qaidam Lake in the northern Tibetan Plateau were used as a sensitive indicator for palaeoclimate. Their geochemical characteristics were investigated, together with an analysis of 2600 m long successive gamma-ray logging data from the whole JS2 drillcore, to understand the mid-Miocene climate transition in the Tibetan Plateau. By comparing the gamma-ray curve of the mixed sediments with global temperature, the Middle Miocene Climatic Optimum event can be easily identified. Further, the detailed petrological features and geochemical data of lacustrine fine-grained mixed sediments from a 400 m drillcore show oxidizing, high-sedimentation rate and brackish-saline water conditions in a semi-arid climate during the Middle Miocene period, demonstrating a dryer climate in the Qaidam Basin than in the monsoon-sensitive regions in Central Asia. These fine-grained mixed sediments have recorded climate drying before 15.3 Ma that represents a climatic transition within the Middle Miocene Climatic Optimum; increasing carbonate-rich mixed sediments, decreasing algal limestone layers and decreasing lacustrine organic matter are indicators of this transition. Regional tectonic events include the retreat of the Paratethys from Central Asia at ∼15 Ma and the synchronous tectonic reorganization of the Altyn-Tagh fault system and the northeastern Tibetan Plateau. We find that global climate change is the primary factor affecting the overall characteristics and changes of the Neogene climate in the Qaidam Basin, including the occurrence of the Middle Miocene Climatic Optimum and the cooling and drying tendency, while the regional events are a secondary factor.

Activity of the Baiganhu Fault of the Altyn Tagh Fault System, northern Tibetan Plateau: Insights from zircon and apatite fission track analyses

The geometry and kinematics of first-order structural systems on the Tibetan Plateau (TP) are key to understanding how the continental crust and lithosphere deformed during the India-Asia collision. The Altyn Tagh Fault (ATF), which is a large-scale fault bounding the northern edge of the Tibetan Plateau (NTP), absorbed as much as one-third of the total convergence in the collision between India and Eurasia. The Baiganhu Fault, in the western Qimen Tagh Mountains on the NTP, is recognized as belonging to the ATF and has played an important role in the development of its adjacent region. Due to the high elevation and harsh working conditions, this fault has received little attention, and the timing of its activation has not been thoroughly researched. In this study, we collected granite samples from close to the Baiganhu Fault in the Qimen Tagh Mountains, and used zircon and apatite fission track dating to constrain the timing of activation for this fault. The fission track ages and HeFTy modeling results reveal two rapid cooling stages along the Baiganhu Fault: one during the Jurassic-cretaceous (~180–120 Ma) and the second since the mid-Miocene (~15–10 Ma), consistent with other regions on the NTP. The first fast exhumation event was a far-field response to the Lhasa-Qiangtang collision, and the second stage most likely resulted from crustal thickening, with a connection to the ATF occurring at around ~15–10 Ma.

Development and Interplay of Two Orthogonal Fault Systems in the NW Qaidam Basin, Northern Tibetan Plateau

How fold and thrust belts (FTBs) evolve over time and space in a transpressional regime remains poorly understood. Based on high-resolution 3D seismic reflection data and remote sensing images, we herein present a detailed structural analysis of the Cenozoic faults in the NW margin of the Qaidam Basin that is bounded to the north by the left-reverse Altyn Tagh fault system. Two sets of orthogonal, basement-involved faults with contrasting geometries, kinematics, and temporal development are identified. One set consists of generally E-W-striking, N-dipping, reverse faults with a component of sinistral shear. They are parallel or subparallel to the Altyn Tagh fault system, led to southward tilting of the basement, and formed a local unconformity between the middle Miocene Shangyoushashan formation and underlying strata. They developed in an out-of-sequence order, and were mostly active during 43.8–15.3 Ma but in relatively tectonic quiescence with limited weak reactivation since then. The second set is mainly composed of the NNW-striking reverse faults with dextral shear components. They are approximately perpendicular to the Altyn Tagh fault system, and intensively active since ∼15.3 Ma, much later than the initiation of the E-W-striking faults. Together with published results, we ascribe the development of these two sets of orthogonal faults as the transition from transpression to left lateral slip on the central segment of the Altyn Tagh fault system. The two fault sets interplayed with each other in two ways: 1) the older E-W-striking faults were offset by younger NNW-striking faults, and 2) the younger NNW-striking faults curved to link with the preexisting E-W-striking faults. Our findings reveal that transpressional-dominated FTBs evolve in a more complicated way than the contractional-dominated ones, and more site-based case studies are needed to reveal the underlying primary principles.

Contributions of Triassic Tectonism to Build the Northern Tibetan Plateau: Insights From Tectonic Evolution of the Jinhongshan Range, Central Altyn Tagh Fault System

AbstractClarifying the contributions of pre‐Cenozoic and especially the Mesozoic tectonism to build crustal architecture of the Tibetan plateau is important, especially for evaluating the role of Cenozoic Indo‐Asian collision in creating the present‐day plateau. However, how the Mesozoic tectonism evolved and its influence on the Cenozoic strain distribution remain enigmatic. We provide constraints on these issues by reporting evidence of Triassic (232–223 Ma) and Eocene crustal shortening in the Jinhongshan range of North Tibet, based on coupled structural, zircon U‐Pb, and40Ar/39Ar studies. Triassic shortening was accomplished by two stages manifested as top‐SSE thrust shear (D1) followed by sinistral oblique shear along the ENE trending Jinhongshan shear zone and tight folding (D2), related to ~NNE‐SSW transpression under greenschist‐ to amphibolite‐facies conditions. Such shortening occurred coevally with regional‐scale magmatism, cooling, and exhumation, indicating significant Mesozoic tectonism capable of generating thickened crust and high elevation of North Tibet. We attributed the shortening to far‐field stress effects of terrane collisions between Kunlun and Qiangtang, in which the comparable Jinhongshan and Dangjin shear zones might have formed a continuous, high‐strain zone accommodating relative motion between Tarim and Kunlun‐Qaidam. Eocene shortening (D3) is documented by ENE trending open folds and thrusts, kinematically compatible with left‐lateral activity along the Cenozoic Altyn Tagh fault system. The Triassic Jinhongshan‐Dangjin zone shows a spatial consistency with the Cenozoic Altyn Tagh fault system, implying that at least some segments of this Cenozoic fault system follow more ancient structures. Such evidence reinforces a decisive role of the Triassic tectonic discontinuity in localizing Cenozoic deformation.

Detailed mapping of the surface rupture of the 12 February 2014 Yutian Ms7.3 earthquake, Altyn Tagh fault, Xinjiang, China

Large-scale detailed mapping plays a key role in revealing the rupture characteristics and mechanisms of strong earthquakes. Relatively few studies have been performed on the surface ruptures of large earthquakes in central and western Tibet due to its remote nature and high elevation. Based on high-resolution unmanned aerial vehicle (UAV) photography, we mapped the coseismic surface rupture of the 2014 Yutian Ms7.3 earthquake. Along the western Altyn Tagh fault system, the earthquake produced ≈37 km of surface rupture along the South Xor Kol fault (southern section S1), Xor Kol fault (central section S2) and Ashikule fault (northern section S3). Section S1 has a 16-km-long surface rupture with an average sinistral offset of 52±25 cm and a maximum offset of ~90 cm, while section S3 has a 14.2-km-long surface rupture with an average sinistral offset of 36±21 cm and a maximum offset of ~84 cm. A compilation of 5308 cracks yields an average crack width along the southern section of 85±71 cm and a maximum width of ~700 cm; the average width along the central section is 39±21 cm, and the maximum width is 243 cm; and the average width along the northern section is 61±44 cm with a maximum of ~340 cm. In addition, the average cumulative opening across rupture zone is 3.4±2.9 m along the southern section, with a maximum of ~17 m; 4.3±3.6 m along the central section, with a maximum of ~13 m; and 1.7±1.6 m along the northern section, with a maximum of ~6 m. Evidently, the average crack width and cumulative opening decrease towards bends and steps along the fault. A global synthesis of surface rupture distributions corresponding to strike-slip earthquakes indicates that the rupture zone is wider near the complex parts of fault geometries (such as bends, steps and fault bifurcations) than along straight sections, suggesting that the fault geometry has an obvious control on the surface rupture width. The widespread cracks at the intersection between the Xor Kol and South Xor Kol faults may indicate that an extensional regime is more likely to produce distributed offfault deformation, which provides an observational constraint for the numerical simulation of dynamic rupture on a fault. In addition to coseismic surface rupture, the Yutian earthquake also produced a large number of gravity-driven slides on alluvial fans with gentle slopes. The friction efficiency of the water-bearing salt layer beneath fans could decrease the sliding threshold and trigger instability under surface shaking. These distributed deformations and gravity-driven slides reflect the coupling between the rupture propagation and fault geometry and indicate that the rupture may have propagated in two directions along the Ashikule fault after passing through a step. Therefore, the investigation of coseismic surface rupture provides important observational constraints on the dynamic rupture process.

Segmentation and termination of the surface rupture zone produced by the 1932 Ms 7.6 Changma earthquake: New insights into the slip partitioning of the eastern Altyn Tagh fault system

AbstractThe 1932 Ms 7.6 earthquake struck the active Changma fault in the NE Tibetan Plateau, and produced a distinct surface rupture along the fault zone. However, the segmentation and termination of the surface rupture zone are still unclear. In this paper, the active tectonic analyses of multiple satellite images complemented by field investigations present the 120-km-long surface rupture zone, which can be divided into five discrete first-order segments, ranging from 14.4 to 39.56 km in length, linked by step-overs. Our results also indicate that the 1932 rupture zone could jump across step-overs 0.3–4.5 km long and 2.2–5.4 km wide in map view, but was terminated by a 6.3-km-wide restraining step-over at the eastern end. The left-lateral slip rates along the mid-eastern and easternmost segments of the Changma fault are 3.43 ± 0.5 mm/yr and 4.49 ± 0.5 mm/yr since 7–9 ka, respectively. The proposed tectonic models suggest that the slip rates on the Changma fault are similar to the slip rate on the eastern segment of the Altyn Tagh fault system near the junction point with the Changma fault. These results imply that the Changma fault plays a leading role in the slip partitioning of the easternmost segment of the Altyn Tagh fault system.

Structural analysis and tectonic evolution of the western domain of the Eastern Kunlun Range, northwest Tibet

AbstractThe Tibetan Plateau, the largest highland on Earth, formed due to the collision of India-Asia over the past 50–60 m.y., and the evolution of the Tibetan Plateau impacts our knowledge of continental tectonics. Examination of the northernmost margin of the Tibetan Plateau is key to unravelling the deformation mechanisms acting in northern Tibet. The left-slip Altyn Tagh fault system defines the northwest margin of the Tibetan Plateau, separating the Western and Eastern Kunlun Ranges in the southwest. Both Cenozoic and pre-Cenozoic crustal deformation events at this junction between the Altyn Tagh and Kunlun Ranges were responsible for the construction of northwestern Tibet, yet the relative contribution of each phase remains unconstrained. The western domain of the Eastern Kunlun Range is marked by active NE-trending, left-slip deformation of the Altyn Tagh fault and an E-striking Cenozoic thrust system developed in response India-Asia collision. To better constrain the Paleozoic Altyn Tagh and Kunlun orogens and establish the Cenozoic structural framework, we conducted an integrated investigation involving detailed geologic mapping (∼1:50,000 scale), U-Pb zircon geochronology, and synthesis of existing data sets across northwestern Tibet. Our new zircon analyses from Paleoproterozoic–Cretaceous strata constrain stratigraphic age and sediment provenance and highlight Proterozoic–Paleozoic arc activity. We propose a tectonic model for the Neoproterozoic–Mesozoic evolution of northwestern Tibet wherein restoration of an ∼56-km-long balanced cross section across the western domain of the Eastern Kunlun suggests that Cenozoic minimum shortening strain was ∼30% (∼24 km shortening). Field evidence suggests this shortening commenced after ca. 25–20 Ma, which yields an average long-term shortening rate of 1.2–0.9 mm yr–1 and strain rates of 4.7 × 10–16 s–1 to 2.3 × 10–16 s–1. Geometric considerations demonstrate that this contractional deformation did not significantly contribute to left-slip offset on the Altyn Tagh fault, which has ∼10 mm/yr slip rates.

Middle Miocene reorganization of the Altyn Tagh fault system, northern Tibetan Plateau

Middle Miocene reorganization of the Altyn Tagh fault system, northern Tibetan Plateau

Tectono-magmatic rejuvenation of the Qaidam craton, northern Tibet

Ascertaining the enigmatic characteristics of the crystalline basement of the Qaidam basin, the deepest intracontinental basin yet located in the highest orogenic plateau with the thickest continental crust, has broad implications for the Cenozoic basin evolution, in particular, and intracontinental tectonics of Asia, in general. We carried out a comprehensive investigation on the ages and geochemical-isotopic characteristics of the Qaidam and Suganhu basement rocks obtained from drill-cores. Petrological observations and U-Pb zircon dating (LA-ICP-MS) of granitoid samples from drill cores indicate that Early Neoproterozoic, Early Paleozoic and Late Paleozoic-Mesozoic intrusions are largely represented, suggesting that the Qaidam and Suganhu blocks were involved into three tectono-magmatic episodes. Similar whole-rock geochemistry and Sr–Nd isotopic characteristics between the Early Neoproterozoic granitoids beneath the Qaidam basin and the contemporaneous basement rocks in the surrounding orogenic belts confirm the existence of pervasive Early Neoproterozoic metamorphism and magmatism along the present-day northern Tibetan Plateau. By comparing the trace and rare earth elements patterns as well as the Sr-Nd compositions of the Ordovician arc-related granitoids and Silurian-Devonian post-collisional granitoids beneath the Qaidam and Suganhu basins with the corresponding granitoids from the surrounding orogenic belts, we assert that the Proto-Tethys subduction events that were recorded within the Eastern Kunlun, Altyn Tagh and the Qilian Shan orogenic belts, were different. They generated distinctive subduction-related arc magmas, whereas the closure of the oceanic basins resulted in the amalgamation of the orogenic belts inducing subsequent extensive post-collisional magmatism within the Qaidam block. The widespread Permian and Triassic granitoids beneath the northwestern/northern Qaidam basin mainly involved a lower crust or a crust-mantle source including Mesoproterozoic crust. They demonstrate that the influence of the Paleo-Tethys evolution penetrated the Qaidam block northwards, reaching to the northern edges of the block. We conclude that the Qaidam block is not a craton as typical as the rigid Tarim block, but pertains to a tectono-magmatic rejuvenated craton, which is not mechanically-stronger than its surrounding regions. However, trapped between the lithospheric left lateral strike-slip Altyn Tagh fault system to the northwest and the Qilian Shan transpressional system to the northeast, the Qaidam block forms a relatively stable domain that escaped from significant Cenozoic deformation.

Coseismic Surface Ruptures Associated with the 2014Mw 6.9 Yutian Earthquake on the Altyn Tagh Fault, Tibetan Plateau

Field investigations reveal that the 2014 M w 6.9 Yutian earthquake on the left‐lateral strike‐slip Altyn Tagh fault (ATF) system, Tibetan Plateau, produced an ∼25‐km‐long surface rupture zone that contains conjugate Riedel shear faults. The coseismic surface ruptures occurred mainly along two parallel east‐northeast‐trending active left‐lateral strike‐slip faults. Rupture also occurred in a conjugate, west‐northwest‐trending zone along an active right‐lateral strike‐slip fault. The east‐northeast‐trending ruptures are concentrated in a zone of <500‐m wide and ∼25‐km long, and are characterized by Riedel shear structures including distinct shear faults (Y) with a maximum sinistral displacement of ∼1 m, right‐stepping en echelon cracks, and mole tracks. In contrast, the west‐northwest‐trending ruptures occur within a zone of up to 1.5‐km wide and ∼4‐km long in the jog area between the two parallel east‐northeast‐trending faults, and this zone is characterized by discontinuous shear faults with dextral displacements of <0.5 m, left‐stepping en echelon cracks, and mole tracks, all oriented oblique to the east‐northeast‐trending rupture zones at an angle of 30°–40°. The lengths and displacements of the coseismic surface ruptures measured in the field are comparable with those obtained from the empirical relationships between magnitude and coseismic surface rupture length and displacement. Our findings demonstrate that the coseismic conjugate Riedel faulting was controlled mainly by preexisting active faults of the ATF system, reflecting the present‐day tectonic stress field associated with the ongoing penetration of the Indian Plate into the Eurasian Plate.

The First Quantitative Slip‐Rate Estimated Along the Ashikule Fault at the Western Segment of the Altyn Tagh Fault System

The First Quantitative Slip‐Rate Estimated Along the Ashikule Fault at the Western Segment of the Altyn Tagh Fault System

Late Quaternary slip-rate along the central Bangong-Chaxikang segment of the Karakorum fault, western Tibet

Insight into the spatial and temporal changes of slip-rate is essential to understand the kinematic role of large strike-slip faults in continental collision zones. Geodetic and geologic rates from present to several million years ago along the Karakorum fault range from 0 to 11 mm/yr. Here, we determine the first late Quaternary slip-rate at the southern end of the linear Bangong-Chaxikang segment of the Karakorum fault, using cumulative offsets (20–200 m) of fans and terraces at three sites, as well as 74 new 10 Be surface-exposure ages to constrain the age of these offset geomorphic markers. The rate is >3 mm/yr at sites Gun and Chaxikang, and it is >1.7–2.2 mm/yr at the Gar fan site. Together with rates obtained along the southernmost Menshi-Kailas segment, the Karakorum fault slip-rate seems to increase southeastward from south of Bangong Lake to Kailas (from >3 to >8 mm/yr). These Karakorum fault slip-rate data (>3–8 mm/yr), together with the total length of the fault (>1000 km) and its initiation age (>13–23 Ma), confirm that the Karakorum fault is the major fault accommodating dextral strike-slip motion NE of the western Himalayas. The dextral Karakorum fault in the south and the conjugate left-lateral Longmu Co–Altyn Tagh fault system in the north are thus the major strike-slip faults of western Tibet, which contribute to eastward extrusion of Tibet.

Middle Miocene–Pliocene activities of the North Altyn fault system: evidence from apatite fission track data

In this study, apatite fission track (AFT) analyses from opposite sides of the Jianglisai fault are used to constrain the timing of fault activity. Samples collected on the hanging wall have AFT ages between 10 ± 1 and 15 ± 2 Ma and a mean track length ranging from 13.1 ± 0.2 to 13.5 ± 0.2 μm. Samples collected on the footwall have AFT ages between 7.4 ± 0.6 and 9.0 ± 0.9 Ma and a relatively short mean track length that ranges from 11.3 ± 0.2 to 11.6 ± 0.2 μm. AFT modeling revealed that each side experienced two rapid cooling events that were related to tectonic stresses and deformation propagating in a northwestern direction. Combined with electron spin resonance dating constraints, we interpret the rapid cooling of the hanging wall during the Middle Miocene (17–14 Ma) as having recorded that the Jianglisai fault has been active at or prior to ~17 Ma. Both sides of the fault recorded the exhumation event that occurred at approximately 8 Ma, which is responsible for developing the fold-and-thrust belt along the mountain front. The Early Pliocene (about 5 Ma) cooling event indicated that the thrusting-related exhumation in the Jianglisai fault system was a continuously gradual intensified process. The North Altyn Tagh fault system was formed through stepwise thrusting from southeast to northwest during the Middle Miocene to Early Pliocene (17–5 Ma). Since then, the rigid Tarim plate provided constraint on the northward propagation, which likely caused the change from compressional thrusting to thrusting with a left-lateral strike-slip component of the North Altyn Tagh fault system.