Altyn Tagh Fault System Research Articles

U-Pb (SHRIMP) and 40Ar/39Ar geochronological constraints on the evolution of the Xingxingxia shear zone, NW China: A Triassic segment of the Altyn Tagh fault system

The development of structures and their age along the segment of the Altyn Tagh fault system, and the eastward extension of the Tianshan orogenic belt, remain speculative. Recent investigations on the structural framework, granitic intrusions, and metamorphic rocks in the eastern Tianshan and adjacent areas show that the NE-striking Xingxingxia sinistral ductile shear zone, NW China, is subparallel to the Altyn Tagh fault zone and is superposed on the eastern Tianshan orogenic belt. U-Pb zircon, sensitive high-resolution ion microprobe (SHRIMP) dating, and muscovite, biotite, and K-feldspar 40 Ar/ 39 Ar thermochronology indicate that sinistral shear along the Xingxingxia shear zone initiated at ∼240–235 Ma, broadly at the same time as initial formation of the Altyn Tagh fault zone, but later than initiation of dextral strike-slip motion along ∼EW-trending eastern Tianshan orogenic belt at ∼270–245 Ma. Formation of the Xingxingxia ductile shear zone was associated with Gondwanaland convergence along the southern margin of the Eurasian continent during the Late Permian–Early Triassic.

Evidence against Quaternary slip on the northern Karakorum Fault suggests kinematic reorganization at the western end of the Himalayan–Tibetan orogen

While the right-slip Karakorum fault is one of the most prominent structures in the Himalayan–Tibetan orogen, its evolution and role in accommodating deformation related to the collision between India and Asia is controversial. Different models interpret the Karakorum fault as either: 1) a long-lived, stable feature analogous to a plate boundary structure, or 2) an evolving fault system with limited displacement (< 200 km) and transient kinematics. While active deformation along the southern segment of the Karakorum fault is well established, neotectonic activity along the fault north of its intersection with the active left-slip Longmu–Co Gozha–Co fault system has not been documented. Analysis of Corona and ASTER satellite images along the northern end of the Karakorum fault zone provide several lines of evidence that show this portion is no longer active: 1) multiple generations of Quaternary glacial and fluvial deposits which can be correlated with previously dated deposits in the region, the oldest of which are > 150 ka, overly the trace of the two strands of the Karakorum fault and show no evidence of tectonic disturbance; 2) older (late Pliocene to early Quaternary) loess deposits which overlie the trace of the fault are either undisturbed, or are cut by small normal fault scarps with no evidence of strike-slip displacement; 3) east–west trending bedrock incised stream valleys up to 500 m deep cross both strands of the fault with no sign of lateral deflection. I suggest that termination of slip along the northern segment of the Karakorum fault occurred in the Pliocene due to southward propagation of the Altyn Tagh fault system along the Longmu–Co Gozha Co fault and impingement of the Karakorum fault. This study suggests that large intracontinental strike-slip faults embedded within orogenic plateaus are transient features which should be expected to have complicated kinematic histories and short life-spans relative to the life of an orogenic belt.

&lt;sup&gt;40&lt;/sup&gt;Ar-&lt;sup&gt;39&lt;/sup&gt;Ar thermochronological evidence for formation and tectonic exhumation of the northern-central segment of the Altyn Tagh Fault System in the Mesozoic, northern Tibetan Plateau

† School of Geophysics and Information Technology, China University of Geosciences, Beijing 100083, CHINA ‡ Geologic Laboratories Center and Department of Geology, China University of Geosciences, Beijing 100083, CHINA § Institute of Geology and Geophysics, Chinese Academy of Science, Beijing 100029, CHINA ¶ Institute of Geology, China Seismological Bureau, Beijing 100029, CHINA # Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, CHINA

Thin‐plate modeling of interseismic deformation and asymmetry across the Altyn Tagh fault zone

Creeping dislocations in an elastic half‐space are commonly used to model interseismic deformation. However, this semi‐infinite conventional model can lead to biased inferences of the slip rate and the fault locking depth. We therefore favor the use of a thin‐plate model sheared at its base in agreement with the current knowledge of the seismogenic thickness of the lithosphere. We apply these two approaches to interpret InSAR data across the Altyn Tagh fault system near longitude 94°E, in a region of clear asymmetry of interseismic velocity distribution. Our results suggest a locking depth of 7–9 km and a present‐day geodetic slip rate of 8–10 mm/yr, consistent with the rate based on GPS measurements at this longitude. We interpret the asymmetric pattern as the joint effect of a rigidity decrease from the Tarim basin north of the fault to the Qaidam basin south of it and of a 5–7 km southward offset of strain concentration from the quaternary northern active fault. This suggests that the rigidity contrast as well as most of the creep at depth occurs on the southern geological fault.

The Aksay segment of the northern Altyn Tagh fault: Tectonic geomorphology, landscape evolution, and Holocene slip rate

Millennial slip rates have been determined for the Altyn Tagh fault (ATF) at three sites near Aksay (∼94°E) in northeastern Tibet by dating fluvial channels and terrace riser offsets with radiocarbon and 10Be‐26Al surface exposure dating. Up to nine main surfaces are defined on the basis of morphology, elevation, and dating. The abandonment age of some surfaces is constrained by radiocarbon dating, which typically coincides with the youngest cosmogenic ages for a particular surface. Older surface exposure ages are taken to represent the duration of terrace emplacement. Cumulative offsets range from 20 to 260 m and fall in distinct groups, indicative of climatically modulated regional landscape formation. Most samples are younger than ∼14 ka and postdate the Last Glacial Maximum. The end of the early Holocene optimum marks the boundary between the ages of the two main terrace levels at 5–6 ka. At this longitude the ATF is divided into a northern and southern branch. The northern ATF should thus yield a minimum rate for the ATF system. Slip rate estimates using the abandonment age of the overlying level for fill terraces or channels and the emplacement of the underlying level for strath terraces give 30 consistent results, yielding an average Holocene rate of 17.8 ± 3.6 mm/yr. It is ∼9 mm/yr less than the long‐term rate obtained near Tura at ∼87°E (26.9 ± 6.9 mm/yr), in keeping with the inference of an eastward decreasing rate on the ATF, due to increased thrusting to the south. However, it remains twice the rate determined by GPS studies.

40Ar/39Ar thermochronological evidence for formation and Mesozoic evolution of the northern-central segment of the Altyn Tagh fault system in the northern Tibetan Plateau

Research Article| September 01, 2005 40Ar/39Ar thermochronological evidence for formation and Mesozoic evolution of the northern-central segment of the Altyn Tagh fault system in the northern Tibetan Plateau Yu Wang; Yu Wang 1Geologic Laboratories Center and Department of Geology, China University of Geosciences, Beijing 100083, China Search for other works by this author on: GSW Google Scholar Xuemin Zhang; Xuemin Zhang 2School of Geophysics and Information Technology, China University of Geosciences, Beijing 100083, China Search for other works by this author on: GSW Google Scholar Erchie Wang; Erchie Wang 3Institute of Geology and Geophysics, Chinese Academy of Science, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Jinfeng Zhang; Jinfeng Zhang 4Department of Geology, China University of Geosciences, Beijing 100083, China Search for other works by this author on: GSW Google Scholar Qi Li; Qi Li 5Institute of Geology, China Seismological Bureau, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Guihua Sun Guihua Sun 6Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China Search for other works by this author on: GSW Google Scholar Author and Article Information Yu Wang 1Geologic Laboratories Center and Department of Geology, China University of Geosciences, Beijing 100083, China Xuemin Zhang 2School of Geophysics and Information Technology, China University of Geosciences, Beijing 100083, China Erchie Wang 3Institute of Geology and Geophysics, Chinese Academy of Science, Beijing 100029, China Jinfeng Zhang 4Department of Geology, China University of Geosciences, Beijing 100083, China Qi Li 5Institute of Geology, China Seismological Bureau, Beijing 100029, China Guihua Sun 6Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China Publisher: Geological Society of America Received: 20 Jul 2004 Revision Received: 12 Dec 2004 Accepted: 10 Jan 2005 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2005) 117 (9-10): 1336–1346. https://doi.org/10.1130/B25685.1 Article history Received: 20 Jul 2004 Revision Received: 12 Dec 2004 Accepted: 10 Jan 2005 First Online: 02 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 Yu Wang, Xuemin Zhang, Erchie Wang, Jinfeng Zhang, Qi Li, Guihua Sun; 40Ar/39Ar thermochronological evidence for formation and Mesozoic evolution of the northern-central segment of the Altyn Tagh fault system in the northern Tibetan Plateau. GSA Bulletin 2005;; 117 (9-10): 1336–1346. doi: https://doi.org/10.1130/B25685.1 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 SocietyGSA Bulletin Search Advanced Search Abstract To better constrain the probable timing of formation and evolution of the Altyn Tagh sinistral strike-slip system in the Mesozoic, a 40Ar/39Ar thermochronological study has been carried out in the north-central segment of the Altyn Tagh fault system, the northern margin of the Qaidam Basin, and the eastern Kunlun orogenic belt. Muscovite, biotite, and K-feldspar separated from mylonite, granite, pegmatite, and metamorphic rocks have been analyzed. The range of 40Ar/39Ar data and structural evidence indicate that a peak metamorphic event in terranes bordering the Altyn Tagh fault system occurred between 450 and 420 Ma. At ca. 250–230 Ma there is evidence for initial sinistral strike-slip shearing. Sinistral strike-slip deformation occurred later along the Altyn Tagh fault system at 165–160 Ma and 100–89 Ma, respectively.Cooling histories in the northern margin of the Qaidam Basin and the eastern Kunlun orogenic belt show that these areas also experienced rapid cooling ca. 250–230 Ma, as was the case for the early Altyn Tagh fault system. This regional tectonic and cooling process indicates that the initial formation of the Altyn Tagh sinistral slip fault system occurred in latest Permian–Early Triassic time and was coupled with, or related to, suturing in the northern margin of the Qaidam Basin and the Kunlun orogenic belt. Cooling events along the Altyn Tagh fault system between 165 and 160 Ma and 100–89 Ma were accompanied by differential closure along the Bangong Lake–Nujiang suture zone in its eastern and western sectors during the Middle-Late Jurassic and Early Cretaceous, respectively (Zhao et al., 2001; Wang et al., 2002). You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Oligocene‐Miocene Tectonics and Sedimentation along the Altyn Tagh Fault, Northern Tibetan Plateau: Analysis of the Xorkol, Subei, and Aksay Basins

Tertiary basins adjacent to the northern edge of the Tibetan Plateau include both giant intracontinental sedimentary basins such as Tarim and Qaidam and smaller basins directly related to the evolution of the Altyn Tagh strike‐slip fault system and nearby fold‐thrust belts. Three examples of these smaller basins that formed during early evolution of the Altyn Tagh fault system are the Xorkol, Aksay, and Subei basins. The Xorkol basin was the site of nonmarine siliciclastic sedimentation in alluvial fan, playa, and fluvial environments from at least the mid‐Oligocene through the Miocene. Sediment was delivered to the basin from source areas uplifted by basin‐bounding thrust faults and from the opposite side of the Altyn Tagh fault. The age of the Aksay basin is more poorly constrained, but it also contains Oligocene(?)‐Miocene(?) nonmarine clastic strata that were derived from the southern side of the Altyn Tagh fault and adjacent thrust‐fault‐bounded uplifts. The Subei basin is characterized by similar Oligocene‐Miocene fluvial, playa, and alluvial fan deposits; however, in this basin, sediment was derived only from adjacent reverse‐fault‐bounded highlands rather than from across the Altyn Tagh fault. Differences in the lithostratigraphy, depositional environments, clast composition, and paleocurrent directions demonstrate that these basins formed as individual entities and do not represent remnants of a regionally extensive basin that was later dislocated by strike‐slip faulting. Thus, these basins do not represent piercing point pairs, as was previously suggested. However, because they are syn‐slip basins, they do record the relative timing of strike‐slip and reverse faulting and the surface response to deformation, and they provide fault offset data in the provenance relationships between sediment and source terranes on opposite sides of the fault.

Tectonic history of the Altyn Tagh fault system in northern Tibet inferred from Cenozoic sedimentation

The active left-slip Altyn Tagh fault defines the northern edge of the Tibetan plateau. To determine its deformation history we conducted integrated research on Cenozoic stratigraphic sections in the southern part of the Tarim Basin. Fission-track ages of detrital apatites, existing biostratigraphic data, and magnetostratigraphic analysis were used to establish chronostratigraphy, whereas composition of sandstone and coarse clastic sedimentary rocks was used to determine the unroofing history of the source region. Much of the detrital grains in our measured sections can be correlated with uplifted sides of major thrusts or transpressional faults, implying a temporal link between sedimentation and deformation. The results of our studies, together with existing stratigraphic data from the Qaidam Basin and the Hexi Corridor, suggest that crustal thickening in northern Tibet began prior to 46 Ma for the western Kunlun Shan thrust belt, at ca. 49 Ma for the Qimen Tagh and North Qaidam thrust systems bounding the north and south margins of the Qaidam Basin, and prior to ca. 33 Ma for the Nan Shan thrust belt. These ages suggest that deformation front reached northern Tibet only ∼10 ± 5 m.y. after the initial collision of India with Asia at 65–55 Ma. Because the aforementioned thrust systems are either termination structures or branching faults of the Altyn Tagh left-slip system, the Altyn Tagh fault must have been active since ca. 49 Ma. The Altyn Tagh Range between the Tarim Basin and the Altyn Tagh fault has been a long-lived topographic high since at least the early Oligocene or possibly late Eocene. This range has shed sediments into both the Tarim and Qaidam Basins while being offset by the Altyn Tagh fault. Its continuous motion has made the range act as a sliding door, which eventually closed the outlets of westward-flowing drainages in the Qaidam Basin. This process has caused large amounts of Oligocene–Miocene sediments to be trapped in the Qaidam Basin. The estimated total slip of 470 ± 70 km and the initiation age of 49 Ma yield an average slip rate along the Altyn Tagh fault of 9 ± 2 mm/yr, remarkably similar to the rates determined by GPS (Global Positioning System) surveys. This result implies that geologic deformation rates are steady state over millions of years during continental collision.

Large N–S convergence at the northern edge of the Tibetan plateau? New Early Cretaceous paleomagnetic data from Hexi Corridor, NW China

Nine Early Cretaceous paleomagnetic sites have been collected in the Yumen area of the Hexi Corridor (NW China). Magnetic directions isolated at lower temperatures fail the fold test, and lie close to the geocentric axial dipole field direction before tilt correction. High temperature components are carried by magnetite and/or hematite, all with normal polarity, and pass the fold test. The average paleomagnetic pole from the nine sites is at λ=75.5°N, φ=169.9°E ( A 95=7.7°). These results are consistent with those from other areas of the North China block (NCB), but significantly different from those from the Qaidam Basin on the southern side of the Qilian Mountains. They suggest that: (1) the Yumen region behaved as a rigid part of the NCB since at least the Early Cretaceous; (2) 740±500 km of north–south directed convergence has taken place between the NCB and Qaidam, within the Qilian Mountains and (3) extrusion of Qaidam was accompanied by a 23±5° relative rotation with respect to North China. This is larger than implied by the maximum left lateral slip on the Altyn Tagh fault system. The same data imply some 1000±800 km of Cenozoic motion between the Tarim and NCB blocks, which were so far believed to have formed a rigid entity since at least the Jurassic. One interpretation could be that all Tarim and Qaidam Cretaceous paleomagnetic samples from red beds, but not those from Yumen and the NCB, suffered significant inclination shallowing, as observed in Cenozoic red beds from Central Asia. So far, we do not find support for this possibility. Possible tectonic interpretations include: (1) the existence of a large, as yet uncharted, tectonic discontinuity between Tarim and the NCB in the vicinity of the desert corridor near 95–100°E longitude; (2) the occurrence of significant deformation within southwestern Tarim, to the north of Yingjisha where paleomagnetic sites were obtained, or (3) persistent clockwise rotation of Tarim with respect to the NCB, for at least 20 Ma, at the rate found for current block kinematics.

Crustal deformation along the Altyn Tagh fault system, western China, from GPS

We collected GPS data from the southern Tarim basin, the Qaidam basin, and the western Kunlun Shan region between 1993 and 1998 to determine crustal deformation along the Altyn Tagh fault system at the northern margin of the Tibetan plateau. We conclude from these data that the Altyn Tagh is a left‐lateral strike slip fault with a current slip rate of ∼9 mm/yr, in sharp contrast with geological estimates of 20–30 mm/yr. This contrast poses an enigma: because the GPS data cover a wider region than the geologic data, they might be expected to reveal somewhat more slip. We also find that the Tarim and Qaidam basins behave as rigid blocks within the uncertainty of our measurements, rotating clockwise at a rate of ∼11 and ∼4.5 nrad/yr, respectively, with respect to the Eurasia plate. The rotation of the Tarim basin causes convergence across the Tian Shan, increasing progressively westward from ∼6 mm/yr at 87°E to ∼18 mm/yr at 77°E. Our data and other GPS data suggest that the Indo‐Asia collision is mainly accommodated by crustal shortening along the main Himalayan thrust system (∼53%) and the Tian Shan contractional belt (∼19%). Eastward extrusion of the Tibetan plateau along the Altyn Tagh and Kunlun faults accommodates only ∼23% of the Indo‐Asia convergence.

Geodetic evidence for a low slip rate in the Altyn Tagh fault system

The collision between India and Asia has been simulated with a variety of computational models that describe or predict the motions of the main faults of east Asia. Geological slip-rate estimates of 20-30 mm yr(-1) suggest that the largest of these faults, the 2,000-km-long Altyn Tagh fault system on the northern edge of the Tibetan plateau, absorbs as much of the Indo-Asian convergence signal as do the Himalayas--partly by oblique slip and partly by contraction and mountain growth. However, the predictions of dynamic models for Asian deformation and the lower bounds of some geological slip-rates estimates (3-9 mm yr(-1); refs 7, 8) suggest that the Altyn Tagh system is less active. Here, we report geodetic data from 89-91 degrees E that indicate left-lateral shear of 9 +/- 5 mm yr(-1) and contraction of 3 +/- 1 mm yr(-1) across the Altyn Tagh system. This result--combined with our finding that, at 90 degrees E, Tibet contracts north-south at 9 +/- 1 mm yr(-1)--supports the predictions of dynamic models of Asian deformation.

Is the North Altyn fault part of a strike-slip duplex along the Altyn Tagh fault system?

Is the North Altyn fault part of a strike-slip duplex along the Altyn Tagh fault system?

Is the North Altyn fault part of a strike-slip duplex along the Altyn Tagh fault system?

Although the Altyn Tagh fault system has played an important role in the Indo-Asian collision, its geometry and tectonic evolution remain poorly known. Between 86° and 92°E, this system is at least 100 km wide and is bounded to the north and south by the North Altyn and Altyn Tagh faults, respectively. Mapping along the Jianglisai reach of the North Altyn fault indicates that Miocene(?) to Pliocene(?) motion was predominantly left to left-reverse slip, with transport vectors trending N45°–60°E. Map relationships suggest that total offset on the fault is >120 km. These results are inconsistent with previous models of the Altyn Tagh fault system in which oblique convergence along the northern margin of the Tibetan Plateau is partitioned into thrusting on the North Altyn fault and left slip on the Altyn Tagh fault. An alternative hypothesis is that the North Altyn fault is the northern boundary of a transpressional strike-slip duplex within which the structurally elevated Altyn Mountains were created. Our model suggests that transpressional deformation may be restricted to this strike-slip duplex and need not characterize the entire margin.

Magnitude of post-Middle Jurassic (Bajocian) displacement on the central Altyn Tagh fault system, northwest China

The Altyn Tagh fault system, a key structural feature in the tectonic collage of central Asia, is an active left-lateral strike-slip fault system. However, its age of initiation, kinematic history, and total magnitude of displacement are not well known. Middle Jurassic nonmarine sedimentary rocks that crop out along the central segment of the Altyn Tagh fault were deposited in a contiguous Tarim-Qaidam foreland-style basin that was geodynamically linked to Mesozoic contraction in the Tian Shan, Bei Shan, Qilian Shan, and Kunlun Shan. This study documents the best evidence of a piercing point to date, consisting of an offset lacustrine shoreline demarcated by Aalenian-Bajocian open lacustrine strata to the west and fluvial and alluvial strata of comparable age to the east. Detrital compositions, palynology, paleocurrents, and lithostratigraphy support correlation of these sections. Restoration of this Jurassic facies boundary indicates 400 ± 60 km of post-Bajocian left-lateral separation on the Altyn Tagh fault. Consistent with this result, restoration of the Jurassic shoreline aligns felsic plutons across the western segment of the Altyn Tagh fault system that may have been left-laterally offset by 360 km. These two pairs of offset features suggest that the current best estimate for net magnitude of post-Bajocian left-lateral separation on the Altyn Tagh fault is about 360 km.

Cenozoic vertical-axis rotation of the Altyn Tagh fault system

Paleomagnetic declination data were collected from Cenozoic strata of the southern rim of the Tarim basin to address whether the Altyn Tagh fault has undergone significant rotation during the Indian-Asian collision. Results from the eastern and central Altyn Tagh fault zone suggest that it has undergone no significant rotation since the Oligocene. This implies that the boundary between the Tarim and Tibet has remained relatively stationary during most of the Cenozoic. In contrast, declination data from the western Kunlun Shan on the eastern limb of the Pamir orocline, where the Karakax segment of the Altyn Tagh fault system terminates, suggest that the range has undergone clockwise rotations of between 19.3° ± 8.6° and 27.8° ± 5.8°. Such rotation is in mirror image with the documented counterclockwise rotation of 20°–50° in the western Pamir orocline and implies relatively small displacements on the Karakorum fault. Our results also suggest that the Karakax fault may have formed as an accommodation zone between the western Kunlun Shan and the Karakorum Mountains.

Neogene and Quaternary faulting in and along the Qinling Shan

The structure of the Qinling Shan mountain range (Shaanxi, China) involves major east-south-east strike-slip faults. Field observations made during two expeditions in 1983 and 1984 show that the faults are active and may have undergone several tens of kilometres of post-Eocene left-lateral displacement. The faults cut the morphology sharply and offset left-laterally small channels. Their trace is marked by cataclastic to mylonitic non-coaxial deformation zones at least 50–100 m wide. The Qinling faults allow the eastward extrusion of south China and may be considered the easternmost continuation of the Altyn Tagh fault system. They link extensional tectonics in northeastern China to the Himalayan collision.