Altyn Tagh Research Articles

Timing and nature of the partial melting processes during the exhumation of the garnet–bearing biotite gneiss in the southern Altyn Tagh HP/UHP belt, Western China

Partial melting of the garnet (Grt)–bearing biotite gneiss from the Jianggalesayi area in the southern Altyn Tagh high pressure (HP) – ultra high pressure (UHP) metamorphic belt has been identified and reported here. Felsic veins were distributed along the foliation plane and deformed together with the Grt–bearing biotite gneiss, which dominated the main outcrop and preserved diagnostic features of anataxis. Highly cuspate and irregular quartz (Qz)-melt and plagioclase (Pl)-melt surrounded or stretched into biotite and/or quartz grains with obvious eroded boundaries further provided the microstructural evidences for partial melting of the gneiss. CL images showed that zircons from the Grt–bearing biotite gneiss were characterized by multizone structures of core – Rim I – Rim II – Rim III. The different zircon zones from the gneiss had integrated recordings of the protolith ages 836–1613 Ma; the peak metamorphic age of 503 ± 5 Ma; the retrograded age of 456 ± 4 Ma; and the anatectic age of 418 ± 3 Ma. Zircons from felsic veins also exhibited core – rim structures on CL images. The felsic veins yielded similar protolith ages (1099–1072 Ma) and anatectic age (417 ± 2 Ma) as the host gneiss. The zircons from the host gneiss and felsic veins had plotted identical crustal evolution curves in the εHf(t) vs. U-Pb age diagram with identical TDM ages. The U-Pb ages and Lu-Hf isotope both suggested that the felsic veins were internally derived by the partial melting of the host gneiss. Moreover, the high content of Al2O3 and Rb in felsic veins indicated that the decomposition of biotite accounted for the partial melting of the gneiss. The temperatures calculated by Ti–in–zircon thermometer for the anatectic zircons from the felsic veins (582–694 °C) were identical to the conditions of the amphibolite facies stage of the Grt–bearing biotite gneiss (T = 619–646 °C), which indicated that the crystallization of the melt had taken place during the amphibolite facies stage of the exhumation. The anatectic ages (418 ± 3 Ma and 417 ± 2 Ma) of the gneiss and felsic veins were determined to be within the range of the fourth episode of the early Paleozoic magmatism (420–385 Ma), which had formed in a post-collisional extensional setting. Therefore, the combination of the magmatic heat events and stress release may have played an important role in the partial melting of the gneiss.

Crustal Deformation of the Altyn Tagh Fault Based on GPS

AbstractKnowledge of the slip behavior of the Altyn Tagh fault (ATF) has significant implications for our understanding of the tectonic deformation of the Tibetan Plateau. In this study, we process Global Positioning System (GPS) data spanning 2009–2017 across the western ATF, merge the solution with recently published GPS velocities, and obtain a dense GPS velocity field for northern Tibet. We introduce an elastic block model and estimate the fault slip rate, interseismic fault coupling (ISC), and seismic moment accumulation rate along the ATF. The estimated left‐lateral strike‐slip rate of the ATF decreases eastward from 12.8 ± 0.4 mm/a to 0.1 ± 0.2 mm/a. Results show a heterogeneous distribution of ISC along the fault, with the fault locking depth varying from 5 to 20 km. The seismic moment accumulation rate is 2.16–2.37 × 1018 N m/km along three segments between Sulamu Tagh and Aksay bends, where the accumulated seismic moment over the last five centuries could be balanced by earthquakes with magnitudes of Mw 7.7, Mw 7.6, and Mw 7.8, respectively. We calculate the ratio of the Indo‐Eurasia convergence accommodated by the ATF and find that 10.3% of the convergence is accommodated along the fault by lateral extrusion; quantitative analysis of the strain rate, however, shows that a large part of the northern Tibet is not well described by elastic block rotation. Consequently, we suggest that a hybrid kinematic model that includes both block‐like and continuous deformation is needed to better delineate the crustal deformation of the Tibetan Plateau.

Provenance analysis of the Yumen Basin and northern Qilian Shan: Implications for the pre-collisional paleogeography in the NE Tibetan plateau and eastern termination of Altyn Tagh fault

Understanding the pre-collisional paleogeography in the NE Tibetan plateau provides insights into the growth mechanisms of the northern portion of the plateau in the Cenozoic. We conducted sandstone petrography analysis and determined U-Pb ages for detrital zircons from Cretaceous sandstone from the Yumen Basin and the northern Qilian Shan. Cretaceous strata in the northern Yumen Basin yield a unimodal age population at 290–240 Ma that indicates primary derivation from Bei Shan. Cretaceous strata in the westernmost Yumen Basin contain zircons of 2.6–2.2 Ga, 2.1–1.7 Ga, 1.4–0.7 Ga, 440–380 Ma and 300–230 Ma, suggesting source derivation from both the Qilian Shan and Bei Shan. Within the northern Qilian Shan, Cretaceous strata yield age populations of 2.8–2.3 Ga, 2.1–1.2 Ga, 480–380 Ma and ca. 270 Ma, indicating derivation from the Qilian Shan. Sandstone composition results show that a sample from the northern Qilian Shan contains more lithic fragments and plots in the recycled orogen field of the quartz-feldspar-lithics (QFL) diagram, while samples from Yumen Basin are more quartz-rich and plot close to the continental block field of the QFL diagram. This compositional difference corresponds to source variation, consistent with the detrital zircon record. Combined with existing sedimentology and low-temperature thermochronology datasets, we suggest the presence of Cretaceous topographic relief in the Bei Shan and Qilian Shan prior to India-Asia collision. Considering >300 km post-Cretaceous left-lateral offset along the Altyn Tagh Fault (ATF) and the consistently similar detrital zircon ages spectra of the samples from the Cretaceous to late Oligocene strata in the Yumen Basin, we infer the paleogeography in the NE Tibetan plateau has been similar from the late Cretaceous to the late Oligocene with ATF termination in the western Yumen Basin instead of having been linked to strike-slip faults in the Alxa or other regions to the east since its initiation.

Control of Altyn Tagh Fault on the Jurassic shale gas in Western Qaidam Basin, north‐west China

AbstractThe shale of the Middle Jurassic Dameigou Formation in Western Qaidam Basin was developed with large thickness, high organic carbon content, and moderate thermal maturity, which means that it has the basic geological conditions for shale gas generation and accumulation are favourable. According to the comprehensive analysis, the Altyn Tagh Fault (ATF) did not uplift in the early–middle Jurassic period, and the Middle Jurassic stable lacustrine sedimentary strata were not affected by the strike‐slip fault, which provided abundant material basis for shale gas generation. Due to the effect of later ATF left‐lateral strike‐slip activity, and the North–South tectonic extrusion movement, the abnormal overpressure derived from Dameigou Formation was formed, which can provide good preservation conditions for shale gas. The interaction between ATF activity and shale deposition jointly controlled the formation and preservation of shale gas in Western Qaidam Basin.

Metamorphic Evolution During Deep Subduction and Exhumation of Continental Crust: Insights from Felsic Granulites in South Altyn Tagh, West China

Metamorphic Evolution During Deep Subduction and Exhumation of Continental Crust: Insights from Felsic Granulites in South Altyn Tagh, West China

Shallow Seismicity Forecast for the India‐Eurasia Collision Zone Based on Geodetic Strain Rates

AbstractGeodetic strain rates from increasing Global Positioning System data provide a promising approach for seismicity forecast. With the strain rate field presented in Zheng et al. (2017, https://doi.org/10.1002/2017JB014465) derived from the most complete and up‐to‐date Global Positioning System data set in the India‐Eurasia collision zone, we forecast the shallow seismicity of this region, and infer that about 11 Mw ≥ 7.5, 36 Mw ≥ 7.0, 109 Mw ≥ 6.5, and 326 Mw ≥ 6.0 earthquakes may occur here every 100 years. We indicate that shallow seismicity forecast may be able to help us distinguish between block and continuum models, and block model cannot well describe the kinematics of the Tibetan Plateau, Tien Shan, West Mongolia, North China, and Myanmar. We suggest that the regions with high forecasted earthquake rates but lack of historical earthquakes are undergoing high seismic risk, such as the west‐central Himalaya (overdue for Mw ≥ 7.5 earthquakes, possibly Mw ≥ 8.0) and the central Altyn Tagh fault (overdue for Mw ≥ 7.0 and Mw ≥ 7.5 earthquakes).

Lateral Rheology Differences in the Lithosphere and Dynamics as Revealed by Magnetotelluric Imaging at the Northern Tibetan Plateau

AbstractDifferences in topography and surface deformation in the northern Tibetan Plateau may reflect variable rheology in the lithosphere. Whether middle to lower crustal flow exists below the region between the eastern Kunlun Shan range and the Qaidam Basin remains debated. We provide electrical resistivity images of three new magnetotelluric (MT) profiles across the Qiman Tagh and the western Qaidam Basin. The new models reveal low‐resistivity anomalies below the Qaidam Basin in the lower crust and generally high‐resistivity crust in the Qiman Tagh range. A low‐resistivity anomaly at the uppermost‐mantle level is imaged below the Qiman Tagh range in the profile close to the Altyn Tagh Fault. This anomaly is possibly connected with partial melting in the lower portion of the thickened Songpan‐Ganzi crust close to the southern end of the study area; the minimum requirements for the low‐resistivity anomaly below the Qiman Tagh are 0.05 wt% water content or 0.02 melt fraction, which may greatly decrease the effective viscosity in the uppermost‐mantle rocks and allow flowing. Consequently, we propose that the crustal flow is not mature below the Kunlun Shan range south of the Qaidam Basin because no continuous and stable low‐resistivity anomaly was imaged at this level. The uppermost‐mantle low‐resistivity anomaly below the Qiman Tagh is a passage that allows the continuous northward transfer of materials in the interior of the plateau. This low‐resistivity channel shallows northward and reaches the lower crust of the southwestern Qaidam Basin.

Paleomagnetic Rotation Constraints on the Deformation of the Northern Qaidam Marginal Thrust Belt and Implications for Strike‐Slip Faulting Along the Altyn Tagh Fault

AbstractDiscordant Cenozoic paleomagnetic rotation results obtained throughout the northeastern Tibetan Plateau have yielded different tectonic models for the evolution of the Altyn Tagh Fault and the northeastern Tibetan Plateau. Here based on detailed existing magnetostratigraphic age constraints, we carried out an in‐depth paleomagnetic study along the Hongliugou section in the middle northern Qaidam marginal thrust belt to address the Cenozoic rotations of this region. A total of 1,342 Jurassic‐Neogene siltstone‐sandstone core samples were collected from 128 sites across 18 time intervals. Rock magnetic analysis suggested that magnetite and hematite are the dominant magnetic carriers. Detailed thermal demagnetization analyses were performed, and the characteristic remanent magnetizations of 90 sites (743 samples) were obtained, which yielded positive fold and reversals tests, indicating that they likely represent primary magnetizations. Detailed paleomagnetic declination versus age analyses revealed three periods of rotations: ~12.5 ± 15.7° statistically insignificant counterclockwise rotations during ~45–33 Ma, successive clockwise rotations of ~32.2 ± 15.4° during ~33–14 Ma, and subsequent statistically insignificant counterclockwise rotations of ~8.7 ± 9.4° after ~14 Ma. These three periods of rotations are similar to those calculated based on previously available magnetostratigraphic data from the nearby Dahonggou section. Based on the integration of these data with other lines of geological evidence, we attributed the latter two periods of rotations to fast strike‐slip faulting along the Altyn Tagh Fault.

Paleogene sedimentation changes in Lenghu Area, Qaidam Basin in response to the India–Eurasia collision

The Cenozoic India–Eurasia collision is evidently recorded in the Qaidam Basin, which is located in the north margin of the Tibetan Plateau. The present study describes a dextrorotary phenomenon at the end of the Eocene in Lenghu Area in the northern Qaidam Basin, discovered in sedimentary and tectonic records. This phenomenon is interpreted to have been a result of the levorotatory movement along the Altyn Tagh Fault (ATF) based on the following evidence. First, provenance, as analyzed by heavy mineral assemblages, was slightly deflected from southwestward to the westward by about 45°. Second, paleocurrent inferred from dip logging and seismic reflection changed clockwise by approximately 25°. Third, there is evidence of increases in fault activity in the area, especially in northwest–southeast-trending branches relative to older west–east-trending branches. Increases in faulting coincide with abrupt increases in sediment supply in the Oligocene, after earlier decreases based on total sand content during the Eocene. Our results demonstrate that the northern margin of the Tibetan Plateau synchronously responded to the initiation and termination of the India–Eurasia collision. The levorotatory strike slip of the ATF was immediately triggered by the complete collision at the end of Eocene, and the strike-slip movement caused the dextrorotary phenomenon in the Lenghu Area.

Geochemistry, Zircon U–Pb Dating and Hf Isotopic Characteristics of Neoproterozoic Granitoids in the Yaganbuyang Area, Altyn Tagh, NW China

AbstractThe South Altyn continental block is an important geological unit of the Altyn Tagh orogenic belt, in which numerous Neoproterozoic granitoids crop out. Granitoids are mainly located in the Paxialayidang–Yaganbuyang area and can provide indispensable information on the dynamics of Rodinia supercontinent aggregation during the Neoproterozoic. Therefore, the study of granitoids can help us understand the formation and evolutionary history of the Altyn Tagh orogenic belt. In this work, we investigated the Yaganbuyang granitic pluton through petrography, geochemistry, zircon U–Pb chronology, and Hf isotope approaches. We obtained the following conclusions: (1) Yaganbuyang granitoids mainly consist of two‐mica granite and granodiorite. Geochemical data suggested that these granitoids are peraluminous calc–alkaline or high‐K calc–alkaline granite types. Zircon U–Pb data yielded ages of 939±7.1 Ma for granodiorite and ∼954 Ma for granitoids, respectively. (2) The εHf(t) values of two–mica granite and granodiorite are in the range of –3.93 to +5.30 and –8.64 to +5.19, respectively. The Hf model ages (TDM2) of two‐mica granite and granodiorite range from 1.59–.05 Ga and 1.62–2.35 Ga, respectively, indicating that the parental magma of these materials is derived from ancient crust with a portion of juvenile crust. (3) Granitoids formed in a collisional orogen setting, which may be a response to Rodinia supercontinent convergence during the Neoproterozoic.

A 6000-year-long paleoseismologic record of earthquakes along the Xorkoli section of the Altyn Tagh fault, China

Long records of paleoearthquakes are essential for understanding earthquake recurrence behavior of active faults and for evaluating regional seismic hazard. However, paleoseismic data on the Altyn Tagh fault (ATF), one of the longest strike-slip fault in Asia, are scarce. We document a long paleoseismic record along the Xorkoli section of the central ATF. Eight and probably nine earthquakes are identified based on event evidence in the form of open fissures, folds, unconformities, and upward fault terminations, with modeled mean (95% confidence) ages of A.D. 1598 (1491–1741) yr (event A), A.D. 797 (676–926) yr (B), B.C. 668 (732–589) yr (C), B.C. 956 (1206–715) yr (D), B.C. 1301 (1369–1235) yr (E), B.C. 2105 (2233–1987) yr (F, probable), B.C. 2663 (2731–2601) yr (G), B.C. 2818 (2878–2742) yr (H), B.C. 3396 (3522–3205) yr (I). The mean recurrence interval is 620 ± 410 yr with a coefficient of variation (COV) of 0.67, indicating that earthquake recurrence is weakly periodic, with individual intervals ranging from as short as 150 yr to as long as 1460 yr. A global compilation of 35 strike-slip paleoseismic sites yields a similar average COV of 0.69. Synthesis of paleoseismic sites from the central ATF indicates that not all earthquakes ruptured to the eastern end of the Xorkoli section, within the Aksay restraining bend. Given that the 420-yr elapsed time since the most recent event, well within a COV of mean interval, a large surface-rupturing earthquake could occur at any time along the central ATF.

Diachronous Growth of the Altyn Tagh Mountains: Constraints on Propagation of the Northern Tibetan Margin From (U‐Th)/He Dating

AbstractThe sinistral Altyn Tagh strike‐slip fault demarcates the northern boundary of the Qinghai‐Tibetan Plateau; however, the significance and timing of activity along the fault are debated. Here new apatite and zircon (U‐Th)/He data are presented, revealing the exhumation history of the Altyn Tagh Mountains from crustal depths of ~2–7 km. Studies of rock samples from the Altun Shan region show that they were located close to the surface during the Early Cretaceous and remained so until about 40 Ma. Samples from the Subei and Dangjin Pass areas, on the other hand, record a period of rapid exhumation at 20 ± 2 Ma, and samples from the Qiemo area record a period of continuous exhumation between ~20 and 12 Ma at a rate of mm/year, plus a further rapid cooling event at 7–5.5 Ma. Thus, significantly more exhumation has occurred toward the southwestern section of the Altyn Tagh Fault Zone, indicating a decrease in tectonic uplift toward the northeast since the Miocene. During the late Miocene, the Tarim Block began to subduct beneath the northern Tibetan margin, resulting in rapid exhumation of the central section of the Altyn Tagh Fault Zone. In accordance with previous studies, the present results support a model of northward propagation and expansion of the Qinghai‐Tibetan Plateau during the Cenozoic.

Paleoseismic study on the Pingdingshan-Annanba segments of the Altyn Tagh Fault based on offset clusters

Previous studies using paleoseismic trenches and numerical models proposed two different fault rupture models for the Pingdingshan-Annanba segments of the Altyn Tagh Fault, which are both poorly validated because of a lack of measurements of surface rupture displacements. In this paper, we use high-resolution satellite imagery to measure offset geomorphic markers. Taking the fault geometry into consideration, the most likely paleoseismic rupture parameters are determined by comparing the results of the cumulative offset probability densities (COPDs) and the empirical relationships of seismic parameter. The results show that the most recent earthquake (1270A.D.-1775A.D.) along the Suoerkuli segment only ruptured the Suoerkuli Valley, with a surface rupture length of 140 km, an average horizontal displacement of 3.12 m and a moment magnitude (Mw) of 7.4–7.6. The penultimate earthquake (676A.D.-1347A.D.) ruptured both the Annanba segment and part of the Suoerkuli segment with an average horizontal displacement of greater than 5 m, a surface rupture length of 120–260 km and Mw 7.4–7.8. The rupture parameters of the above two earthquakes demonstrate that the Suoerkuli and Annanba segments are individual fault segments which can rupture independently with a surface rupture length more than 100 km. The Pingdingshan double bend to the west of the Suoerkuli segment is likely to be an endpoint that inhibits the rupture propagation towards further west.

InSAR-Constrained Interseismic Deformation and Potential Seismogenic Asperities on the Altyn Tagh Fault at 91.5–95°E, Northern Tibetan Plateau

The present-day kinematic features of the different segments of the Altyn Tagh Fault (ATF) have been well-studied using geodetic data. However, on the eastern segment of the ATF at 91.5–95°E, high spatial resolution deformation has not been previously reported. Here, we processed 185 interferometric synthetic aperture radar (InSAR) images from three descending tracks of the C band ERS-1/2 and Envisat satellites spanning 1995–2011 and obtained the average deformation velocity field. Results show a left-lateral motion of ~4 mm/year along the fault-parallel direction across the ATF at 91.5–95°E, which is consistent with Global Positioning System (GPS) observations. The slip deficit rate distribution at shallow depths was resolved through the InSAR deformation velocity using a discretized fault plane. The slip deficit is capable of an Mw 7.9 earthquake, considering the elapsed time of the latest M 7.0 event. Two potential asperities that could be nucleation sites or rupture areas of future earthquakes were delineated based on the coupling coefficient and seismicity distributions along the fault plane. The larger asperity extends more than 100 km along the ATF at depths of 8–12 km. Our InSAR observations support the undeformed blocks model of the Indo-Eurasian collisional mechanism at the northern margin of the Tibetan plateau.

Late Cretaceous to early Eocene deformation in the northern Tibetan Plateau: Detrital apatite fission track evidence from northern Qaidam basin

Unraveling the growth of northern Tibet is crucial to understanding the geodynamic processes of the India-Eurasia collision, evaluating plateau uplift models and reconstructing associated paleoclimate history. However, pre-middle Miocene deformation history of northern Tibet remains poorly understood. We use detrital apatite fission track (detrital AFT) thermochronology of Mesozoic and Cenozoic sedimentary rocks from northern Qaidam basin to constrain the early growth of northern Tibet. Detrital AFT ages of the Mesozoic samples are younger than their depositional ages, indicating that the Mesozoic succession underwent two stages of exhumation after deep burial during 80–61 Ma and 54–47 Ma. Detrital AFT ages of the Cenozoic samples are older than their depositional ages and reveal that their source region experienced two periods of exhumation (peak ages in 86–59 Ma and 54–36 Ma). These results suggest that the northern Tibet successively experienced Late Cretaceous–early Paleocene and early–middle Eocene deformation. The Late Cretaceous–early Paleocene deformation implies that the extent of pre-collisional (India-Eurasia) deformation region in the plateau were much larger than previously known. The static detrital AFT peak ages (54–51 Ma) based on lag-time analysis for the Paleogene samples demonstrate the early Eocene deformation was a rapid and short-lived event, which was a far-field response to the India-Eurasia collision. Hence, we advocate synchronous deformation throughout the northern plateau at the collision time. Lag-time analysis results also demonstrate absence of Oligocene to early Miocene cooling ages and post-Eocene decreasing exhumation rates in the Cenozoic source regions. This suggests relatively quiescent tectonic settings in the Qilian Mountains during the Oligocene–early Miocene and agrees that the lateral strike-slip movement of the Altyn Tagh Fault was accommodated out of the plateau by the end of the early Miocene.

Late Cenozoic tectonic activity of the Altyn Tagh range: Constraints from sedimentary records from the Western Qaidam Basin, NE Tibetan Plateau

The Altyn Tagh range (ATR) is the northern geological boundary of the Tibetan Plateau and plays a key role in accommodating its Cenozoic lithospheric deformation. However, knowledge of the structural style and age of uplift of the ATR is limited and controversial. The Qaidam Basin, in the southeast side of the ATR, provides an outstanding field laboratory for understanding the history and mechanisms of ATR growth. This study presents a detailed sedimentological analysis of a 1040-m-thick late Cenozoic (~17–5.0 Ma) sedimentary sequence from the western Qaidam Basin, together with the analysis of sedimentological data from nearby boreholes and sections. Our aims were to determine the spatiotemporal evolution of the sedimentary sequences in the study area and to explore their response to late Cenozoic tectonic activity in the ATR. The results show three major intervals of the sedimentary characteristics in the study area: ~>17–16 Ma, 10 Ma and <5 Ma, which are closely related to the development of unconformities and growth strata recorded by high-resolution seismic reflection profiles. Combining the results with a comprehensive provenance analysis and with published records of regional climate change and tectonic activity, we discuss the possible factors responsible for the variations in the sedimentary characteristics of the studied sections. We conclude that significant tectonic responses in the western Qaidam Basin during the late Cenozoic were caused by three stages of tectonic activity of the ATR, at ~>17–16 Ma, ~16–10 Ma and ~10 Ma, during which the ATR respectively experienced tectonic uplift, fast strike-slip motion and intense uplift.

Paleoseismic Investigation of the Aksay Restraining Double Bend, Altyn Tagh Fault, and Its Implication for Barrier‐Breaching Ruptures

AbstractFault geometry is recognized as an important control on earthquake rupture extent, magnitude, and recurrence behavior. However, multicycle earthquake rupture simulations indicate that geometrical barriers do not always stop rupture propagation. Stress buildup over multiple prior earthquakes may promote an occasional breach of a barrier, producing a significantly larger rupture. Here we present paleoseismic data from the Aksay restraining double bend of the Altyn Tagh fault, which supports such breaching. The Aksay bend consists of two main strands, which bend together in a broad transpressional configuration. We investigate the paleo‐earthquake histories of both strands to assess the correlation of events within and beyond the bend. The south strand exhibits four very likely paleo‐earthquakes with an average interval of 1,433 ± 57 years and a coefficient of variation (COV) of ~ 0.5. The north strand records four highest‐quality events after 3650 Before Common Era with an average interval of ~1,326 ± 179 years and a COV of ~0.3. The varying recurrence intervals and relatively high COVs indicate that faults within the Aksay bend have only quasi‐periodic rupture recurrence. Comparing the event sequences also suggests a complex rupture history. The penultimate event appears to correlate across the bend, as well as to previously published paleoseismic chronologies both to the east and to the west, which supports it being a barrier‐breaching event. The event histories reported here indicate that multiple earthquakes must terminate within the bend, over several earthquake cycles, in order to arrive at a stress condition suitable for a breaching earthquake rupture.

INTERSEISMIC DEFORMATION ACROSS THE EASTERN ALTYN TAGH FAULT FROM INSAR MEASUREMENTS

Abstract. As a new type of earth observation technique, InSAR has a lot of advantages, such as all-weather, all-time, high precision, high density, wide coverage and low cost. It has been widely used in deformation monitoring. Taking the eastern segment of Altyn Tagh fault (ATF) as the object of the research, this paper discussed the application of multi-temporal InSAR technology in the field of interseismic deformation monitoring. We measured the interseismic deformation along the eastern section of ATF using three neighboring descending tracks SAR data from the ERS and Envisat missions. The results show that, first, the validation of InSAR results is better than 2.5 mm/yr, the calibration of InSAR results is about 1.06 mm/yr. Second, the fault slip rate in this segment is about 4–7 mm/yr, and is in the locked condition. Third, The InSAR velocity profile across the fault is the clear asymmetry with respect to ATF, it may be the combined effect of northern (NATF) and southern (SATF) branches of ATF.

Understanding the geologic evolution of Northern Tibetan Plateau with multiple thermochronometers

The early onset of deformation following the India-Asia collision, Neogene expanse of uplift, and complex systems that comprise strike-slip faults, thrust faults, and intermontane basins characterize the Cenozoic tectonism of Northern Tibetan Plateau and raise two prominent questions in orogenic geodynamics: 1) What mechanism(s) control(s) the transfer of stress related to the India-Asia collision across the distance of >2000km; and 2) Why the development of high topography was delayed in the Northern Tibetan Plateau and what does it reveal about how the internal forces and external boundary conditions evolved. To address these two questions, we reconstruct a holistic spatial-temporal deformation history of the Northern Tibetan Plateau by using a range of thermochronometers, with closure temperature spanning from 350°C to ~60–70°C. This multi-thermochronometer study reveals three stages of faulting related cooling, in the early Cretaceous, in Paleocene-Eocene and in middle-late Miocene. We observe that Paleocene-Eocene deformation was spatially restricted and mostly occurred on reactivated Cretaceous structures, indicating a control of pre-existing weakness on early Cenozoic deformation. Extensive Neogene deformation contrasts with restricted Paleocene-Eocene deformation and relatively quiescent shortening during the Oligocene-early Miocene, which implies a change in the regional tectonics regime. Global plate reconstructions show that this tectonic reorganization is coeval with an increase in Pacific-Asia plate convergence rates. We argue that this change in regional tectonics is a result of increasing constrictive environment of the eastern plate boundary, which changed the behavior of the Altyn Tagh fault—the boundary fault of Northern Tibetan Plateau, causing it to change from feeding slip into structures out of the plateau to feeding slip into structures at plateau margins.

Strain Partitioning and Present‐Day Fault Kinematics in NW Tibet From Envisat SAR Interferometry

AbstractAn 8 year archive of Envisat synthetic aperture radar (SAR) data over a 300 × 500 km2 wide area in northwestern Tibet is analyzed to construct a line‐of‐sight map of the current surface velocity field. The resulting velocity map reveals (1) a velocity gradient across the Altyn Tagh fault, (2) a sharp velocity change along a structure following the base of the alluvial fans in southern Tarim, and (3) a broad velocity gradient, following the Jinsha suture. The interferometric synthetic aperture radar velocity field is combined with published GPS data to constrain the geometry and slip rates of a fault model consisting of a vertical fault plane under the Altyn Tagh fault and a shallow flat décollement ending in a steeper ramp on the Tarim side. The solutions converge toward 0.7 mm/yr of pure thrusting on the décollement‐ramp system and 10.5 mm/yr of left‐lateral strike‐slip movement on the Altyn Tagh fault, below a 17 km locking depth. A simple elastic dislocation model across the Jinsha suture shows that data are consistent with 4–8 mm/yr of left‐lateral shear across this structure. Interferometric synthetic aperture radar processing steps include implementing a stepwise unwrapping method starting with high‐quality interferograms to assist in unwrapping noisier interferograms, iteratively estimating long‐wavelength spatial ramps, and referencing all interferograms to bedrock pixels surrounding sedimentary basins. A specific focus on atmospheric delay estimation using the ERA‐Interim model decreases the uncertainty on the velocity across the Tibet border by a factor of 2.