Karakorum Fault Research Articles

Gas geochemical evidence for the India-Asia lithospheric transition boundary near the Karakorum fault in western Tibet

The lithospheric structure of the Tibetan Plateau plays a key role in explaining the underlying plateau formation mechanism(s) and growth history. Although many studies have focused on the Moho discontinuity, lithosphere boundary, and lithospheric structure of central and eastern Tibet, there are few corresponding constraints for western Tibet. In this contribution, we systematically investigated the lithosphere in western Tibet by analyzing the He and C isotopes of seven hydrothermal spring systems along the southeastern segment of the Karakorum fault. We found a high Rc/Ra ratio (1.298) for springs along the Karakorum fault, suggesting that the fault plays a key role as a lithospheric-scale conduit for fluid uplift after mantle degassing. In addition, we identified two different origins of the gases at thermal springs, which may reflect two distinct mantle sources. We infer that the locations of these springs reflect the boundary between the Indian and Asian mantles, which is consistent with the geophysics-based interpretations of a “mantle suture” along the Karakorum fault. Our work confirms the boundary between the Indian and Asian mantle, which provides geochemical support to the model of the subduction of Indian lithosphere.

Back-arc suture zone along the north margin of the eastern Cimmerian continent

The Cimmerian continent is the north piece of the Gondwana super-continent collaged to the south edge of the Laurasia super-continent during the closure of the Paleo-Tehyan Ocean. Researchers recently have identified the Rushan-Pshart-Longmu Co-Shuanghu-Bitu-Changning-Menglian-Inthanon suture zone as the northern boundary of the eastern Cimmerian continent. However, a detailed correlation of this complicated tectonic zone from Pamir to Sumatra remains unclear. For example, while a back-arc suture is developed in southeast Tibet and Southeast Asia, no evidence of the same suture has been reported in eastern and central Tibet. In this study, we investigate an ophiolite mélange suite exposed in the Deqin back-arc suture of this tectonic zone in eastern Tibet, and interpret it as the northward extension of the Jinghong-Nan River back-arc suture. The mélange includes serpentinites, gabbros, basalts, and minor abysmal radiolarian-bearing cherts, and these rocks appear as isolated blocks in fault contact with Permian strata. Geochemical data of the serpentinites from the Deqin suture and Bitu suture indicate that they are MOR-type and SSZ-type sutures, respectively. Zircon UPb dating of the gabbro and diorite from the Deqin suture yields crystallization ages ranging from ca. 246 Ma to ca. 276 Ma, and a zircon UPb age of ca. 285 Ma is obtained from the Bitu suture. Geochemical analysis shows that the rocks from the Deqin suture have OIB or MORB characteristics, suggesting southwest subduction of the oceanic lithosphere beneath the North Lancangjiang tectonic belt since the Middle Permian. Two Meso-Tethyan magmatic rock samples from the Bitu and the Deqin sutures crystalized at 114 Ma and 111 Ma, respectively, and their geochemical data indicate OIB-type signature. We conclude that the Bangong Co-Nujiang Ocean lithosphere subducted northeastward beneath the Qamdo terrane at a low angle. Based on the correlation between the Rushan-Pshart suture and the Longmu Co-Shuanghu suture, our pre-Cenozoic plate reconstruction suggests that the Karakorum fault right-laterally offset the northern boundary of the Cimmerian continent by 140 ± 10 km. The offset further implies that the Cenozoic deformation of the Tibetan plateau is accommodated mainly by distributed structures rather than by several discrete fault systems.

Hydrogeochemical origin and circulation of spring waters along the Karakorum fault, Western Tibetan Plateau: Implications for interaction between hydrosphere and lithosphere

Geochemical investigation on the origin and circulation of geothermal water is crucial for better understanding the interaction between hydrosphere and lithosphere. Previous studies on the Himalayan geothermal belt mainly distributed in the central and eastern Tibetan Plateau. In this study, water samples (8 hot springs and 1 cold spring) from the Karakorum fault (KKF) zone of western Tibetan Plateau were analyzed for the hydrogeochemical characteristics and isotopic compositions. Three types of spring water along the KKF were classified on basis of ionic concentration and Sr isotopic composition: type A water (HCO3–Mg or Ca), type B water (HCO3–Na) and type C water (Cl–Na). Type A water is originated from the infiltration of meteoric water and the dissolution of silicate/evaporite. Type B water is mainly leached from the metamorphic and granitoid rocks. Type C water is formed by the dissolution of chlorides and sulphates. δD and δ18O isotopes indicate that geothermal fluid along the fault zone was mainly recharged by local precipitation. Moreover, reservoir temperatures of 144.2–208.6°C were estimated by the silica–enthalpy mixing model, and the thermal waters have a relatively deep circulation depth (≥ 7.0 km). Meanwhile, the thermal waters are characterized by extremely high Li, B, Fe and As concentrations and earthquakes frequently happened in the vicinity, suggesting that the KKF is a deep and active fault, which also indicates that the thermal fluids are strongly associated with seismicity. Therefore, thermal fluid can potentially be used as continuous monitoring sites for earthquake forecasting.

Pre-Cenozoic evolution of the Aghil Range (western Tibetan Plateau): A missing piece of the Tibet-Pamir-Karakorum geopuzzle

The Tibetan Plateau, largely derived from the accretion of several Gondwana microplates to the southern margin of Asia since the late Palaeozoic, is the highest and largest topographic relief on Earth. Although the first order geodynamic processes responsible for its pre-Cenozoic evolution are quite well-known, many issues are still debated, among which is the timing of collision of each terrane with the southern margin of Asia. Even more uncertain is the pre-Palaeozoic history of these terranes, due to the lack of basement exposures. As a contribution to understanding the pre-Cenozoic evolution of the Tibetan Plateau, this paper focuses on the Aghil Range, a remote and poorly investigated area close to the Karakorum Fault between Kunlun and Karakorum (Xinjiang, China) in western Tibet. The tectono-metamorphic and magmatic evolution of the Aghil Range is investigated using a multidisciplinary approach that combines field mapping, petrology and geochronology (UPb on titanite, zircon, monazite and xenotime using SHRIMP-RG). We demonstrate that the Aghil Range preserves a coherent slice of Neoproterozoic crystalline basement with a late Palaeozoic sedimentary cover deposited on a passive continental margin during the Gondwana break-up. This represents the westernmost exposure of Precambrian crystalline basement known so far in the Tibetan Plateau. Furthermore, petrological and geochronological results allow reconstructing the Mesozoic poly-metamorphic evolution of this sector of the Tibetan Plateau, which records the evidence of Middle Jurassic (ca. 170 Ma) and Late Cretaceous (66 Ma) collisional events, as well as of the Late Jurassic (ca. 150 Ma) early subduction of an accretionary complex developed on its southern margin. Evidence of Late Cretaceous subduction-related magmatism preceding the last collisional event is also recorded. These results allow tentative correlation of the different terranes of Central Tibet with those of the Pamir-Karakorum Range on both sides of the Karakorum fault.

Present-day distribution of deformation around the southern Tibetan Plateau revealed by geodetic and seismic observations

The modern kinematics in and around the Tibetan Plateau have been widely investigated; however, the deformation distribution pattern describing the crustal kinematics in this region is controversial. Here, we quantify the deformation distribution in the southern Tibetan Plateau by adopting the partitioning ratio of internal to boundary potency rates instead of the individual slip rate data on major faults used in previous studies. The study area was divided into several blocks by major faults based on geological surveys, seismic data and a significance statistical analysis. For each block, the partitioning ratio of the potency rates was calculated by a microplate model using 294 GPS velocities from 13 studies. The deformation distribution derived from the GPS velocities was validated by surface-wave data from 407 earthquake events. After excluding the potency rates from the boundary between the Tibetan Plateau and Indian Plate, the ratio of intrablock potency rates within the southern Tibetan Plateau was 51%. This suggests that the Tibetan deformation is diffusely distributed over a large range. A seismic data analysis indicated that 53% of the historical seismic moments were released in the modeled blocks since 1901, which supported the conclusion based on the GPS velocities. The F-test indicated that the internal strain in most Tibetan blocks cannot be neglected to fit the surface velocities. Thus, the present-day crust in southern Tibet is probably far from a pure rigid block. This is supported by the relatively slow strike-slip rates of two major faults: the Karakorum fault (5.9 ± 0.8 mm yr−1) and Karakorum-Jiali fault (4.4 ± 0.8 mm yr−1 in the east segment, 9.3 ± 0.8 mm yr−1 in the west segment). The large-scale diffuse deformation in the southern Tibetan Plateau reproduced by the microplate model with significant internal strain, with seismic imaging or structural analyses, could further clarify the geodynamic processes in the India-Asia collision zone.

The 2016 Mw 6.7 Aketao earthquake in Muji range, northern Pamir: Rupture on a strike-slip fault constrained by Sentinel-1 radar interferometry and GPS

On 25 November 2016, the Aketao, Xinjiang earthquake occurred on the Muji fault, which is located at the northernmost end of the right-lateral Karakorum Fault (KF). This event provides a rare chance to gain insights into how the stress accumulates in Pamir margin as the Indian plate collides with the Eurasian plate. Space geodetic measurements including InSAR and GPS were used to obtain coseismic surface displacements associated with this earthquake. Based on a finite fault model, the coseismic slip distribution inverted by the combined datasets indicates that the 2016 Aketao event is caused by a primary shallow strike-slip with minor normal-slip at a steep-dipping angle. To explore the real structure of Muji fault, listric fault model inferred by relocated aftershocks as well as the planar fault model, were used in our slip distribution inversion. The results suggest that the optimal fault model should be a highly-dipping planar fault with two separated asperities. The large slip zone is beneath the surface near the epicenter with a maximum slip of 1.1 m, while the small one in the east breaks the surface, in a good agreement with the field seismic geological survey. The total geodetic moment is 1.35 × 1019N∙m, equivalent to Mw 6.7. The nearly pure dextral strike-slip Aketao earthquake, and the recent 2015 Mw 7.2 sinistral strike-slip Tajikstan earthquake in this region, to some extent, manifest the extension motion is dominated in northern Pamir Plateau, in response to the northward convergence between Indian and Eurasian collision.

Cenozoic episodic uplift and kinematic evolution between the Pamir and Southwestern Tien Shan

The Pamir Salient and Southwestern Tien Shan belong to two different systems, which collided due to the continuous northward drift of the Indian Plate during the Cenozoic, resulting in a shortening of ~300km. The uplift history and kinematic evolution of the Pamir-Southwestern Tien Shan remain unclear. In this study, we chose the 2025 m-thick Pakabulake formation in the East Wuqia section, at the southern-most margin of the Southwestern Tien Shan system, to obtain a high-resolution magnetostratigraphic record spanning ~16.61Ma to ~9.78Ma. Based on its high sedimentation rate, stable ca. E-W paleocurrents and stable magnetic susceptibility values, the nearby Southwestern Tien Shan was inferred to have undergone stable uplift during this period of sedimentation. Combining our results with the previous low-temperature thermochronology, magnetostratigraphy and re-calculated block rotations, we conclude that four episodic uplift events occurred in the Pamir-Southwestern Tien Shan during the Cenozoic, at times of ~50–40Ma, ~35–16Ma, ~11–7Ma and <5Ma, and that the first episodic uplift only occurred in the Pamir Salient. In addition, the Pamir Salient underwent a tectonic transformation from entire- to a half-oroclinal bending rotation during the Miocene, caused by activity along the Karakorum Fault and Kashgar-Yecheng Transfer System.

Mapping the Geothermal System Using AMT and MT in the Mapamyum (QP) Field, Lake Manasarovar, Southwestern Tibet

Southwestern Tibet plays a crucial role in the protection of the ecological environment and biodiversity of Southern Asia but lacks energy in terms of both power and fuel. The widely distributed geothermal resources in this region could be considered as potential alternative sources of power and heat. However, most of the known geothermal fields in Southwestern Tibet are poorly prospected and currently almost no geothermal energy is exploited. Here we present a case study mapping the Mapamyum (QP) geothermal field of Southwestern Tibet using audio magnetotellurics (AMT) and magnetotellurics (MT) methods. AMT in the frequency range 11.5–11,500 Hz was used to map the upper part of this geothermal reservoir to a depth of 1000 m, and MT in the frequency range 0.001–320 Hz was used to map the heat source, thermal fluid path, and lower part of the geothermal reservoir to a depth greater than 1000 m. Data from 1300 MT and 680 AMT stations were acquired around the geothermal field. Bostick conversion with electromagnetic array profiling (EMAP) filtering and nonlinear conjugate gradient inversion (NLCGI) was used for data inversion. The AMT and MT results presented here elucidate the geoelectric structure of the QP geothermal field, and provide a background for understanding the reservoir, the thermal fluid path, and the heat source of the geothermal system. We identified a low resistivity anomaly characterized by resistivity in the range of 1–8 Ω∙m at a depth greater than 7 km. This feature was interpreted as a potential reflection of the partially melted magma in the upper crust, which might correlate to mantle upwelling along the Karakorum fault. It is likely that the magma is the heat source of the QP geothermal system, and potentially provides new geophysical evidence to understand the occurrence of the partially melted magmas in the upper crust in Southwestern Tibet.

River network evolution as a major control for orogenic exhumation: Case study from the western Tibetan plateau

The westernmost Tibetan plateau, despite being internally drained, has a high topographic relief. Here, using apatite (U–Th–Sm)/He and 4He/3He thermochronometry, we reconstruct the exhumation history of the Rutog batholith during the Neogene. Thermal modeling in 1D using the QTQt program indicates that relatively slow cooling occurred from 30 Ma to 19 Ma, which we interpret as an exhumation rate of ∼10 m/Ma. This was followed by two pulses of moderate cooling from 19 to 17 Ma and ∼11 to 9 Ma that correspond to a total exhumation of about 1500 m. Cooling since 9 Ma has been negligible. This differs from exhumation patterns in central Tibet but reveals timing similarities with externally drained portions of southern Tibet. We interpret our cooling constraints as recording two different transitions in western Tibet from an externally to an internally drained system since the Oligocene. External drainage allowed this part of the Tibetan plateau, unlike internally drained portions of central Tibet, to record regional-scale processes. The first cooling event, at about 20 Ma, was likely related to a major geodynamic event such as slab breakoff that induced contemporaneous potassic and ultrapotassic magmatism. The second rapid cooling pulse from ∼11 Ma to 9 Ma and subsequent negligible cooling was most likely controlled by a local factor such as Indus and Shyok river network reorganization caused by dextral motion of the Karakorum fault. We discuss these interpretations and their limitations in this contribution.

Estimation of coupling along the Main Himalayan Thrust in the central Himalaya

We analyze episodic (1995–2010) and permanent GNSS data quantifying interseismic velocities in the Himalaya of Nepal so as to constrain spatial variations in coupling along the Main Himalayan Thrust. To estimate this coupling, we model the MHT with the help of cross sections allowing us to constrain its changes in geometry from far-western Nepal to central and eastern Nepal. We determine that the upper flat of the MHT is nearly totally locked, the crustal ramp is partially locked, and that free slip is localized only along the lower flat north of the Himalaya. This location of increased coupling probably corresponds to the brittle/ductile change in rheology along the MHT and explains the location of very large (greater than the Gorkha 2015 event) earthquake epicenters north of the crustal ramp. Including the simulation of the Western Nepal Fault System in the continuation of the Karakorum fault does not improve simulation of the interseismic velocity field. The 25 April Gorkha earthquake nucleated in a highly coupled part of the upper flat of the MHT and propagated eastward along a less coupled part of the MHT.

Metamorphic P–T conditions and CO2 influx history of medium-grade metapelites from Karakorum, Trans-Himalaya, India

The medium grade metapelites of Pangong-Tso area in the trans-Himalayan region underwent sillimanite-grade metamorphism initiated during the Cretaceous, associated with the collision of the Kohistan arc and the Indian plate with Asia. This paper present results from a petrological and fluid inclusion study to understand the metamorphic P–T conditions and fluid history of these rocks. The calculated phase equilibria in the Na2O–CaO–K2O–FeO–MgO–MnO–Al2O3–SiO2–H2O–TiO2 (NCKFMMnASHT) system suggest P–T conditions of 8kbar and 650°C for the peak metamorphic event. Primary fluid inclusions occur in staurolite and garnet, whereas quartz carries mostly secondary fluid inclusions. The trapped fluids in primary inclusions show initial melting temperatures in the range of −56.9 to −56.6°C, suggesting nearly pure CO2 composition. The secondary fluids are of mixed carbonic-aqueous nature. The re-equilibrated inclusions show annular morphology as well as necking phenomena. The CO2 isochores for the primary inclusions indicate pressures of 6.1–6.7kbar, suggesting that the CO2-rich fluids were trapped during post-peak exhumation of the rocks, or that synmetamorphic carbonic fluids underwent density reversal during isothermal decompression. The secondary CO2–H2O fluids must have been trapped during the late exhumation stage, as their isochores define further lower pressures of 4.8kbar. The morphology of re-equilibrated fluid inclusions and the rapid decrease in pressure are consistent with a near-isothermal decompression trajectory following the peak metamorphism. The carbonic fluids were probably derived locally from decarbonation reactions of the associated carbonate rocks during metamorphism or from a deep-seated reservoir through Karakorum fault.

Comment on “No late Quaternary strike-slip motion along the northern Karakoram fault” published by Robinson et al. in EPSL, 2015

Abstract The northern part of the already highly debated Karakorum fault (KF) in western Tibet (regarding its initiation age, total geological offset and slip-rate) has been argued by Robinson (2009a) and Robinson et al. (2015) to be inactive. This is based on field investigation and satellite images interpretation showing a few km of Quaternary deposits from the southern Tashkorgan basin in the Chinese Pamir, that appear undisturbed by the main branch of the KF. In particular, Robinson et al. (2015) suggested that the Kongur Shan extensional system (KES) is not kinematically related to the KF, and that the latter is only a local fault. Here, we use basic definitions of what is an active strike-slip fault system, as well as re-emphasize the importance of the timescale of observation to discuss whether a fault is active, to demonstrate that the KF and the KES are part of the same fault system. We argue that they together play a significant role in accommodating deformation at the western Himalayan syntaxis, under the form of extensional displacement in the Chinese Pamir.

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.

First tectonic-geomorphology study along the Longmu–Gozha Co fault system, Western Tibet

The Longmu–Gozha Co left-lateral strike-slip fault system (LGCF) is located in remote western Tibet, forming a triple junction with both the Altyn Tagh fault (ATF) and the Karakorum fault (KF), the two major strike-slip faults in the region. The Ashikule, Gozha Co and Longmu Co faults are clear and distinct left-stepping en-echelon faults, together forming the LGCF system. Although poorly documented, quantifying its activity remains a key problem to understand the kinematics and the tectonic history of the westernmost Tibetan Plateau. Indeed, the Karakax fault (NW segment of the ATF), LGCF and KF together control the tectonics of western Tibet which itself controls the extrusion of Tibet towards the east, with the LGCF acting as a natural boundary for eastward motion of the Tibetan Plateau due to India's northward impingement. The LGCF system shows clear and impressive morphological indications of left-lateral active shear, that we quantify using field measurements (terrestrial LIDAR) along with 10Be surface-exposure dating. Our data suggest a slip-rate <3mm/yr, consistent with geodetic and block model studies. While it is on the order of the Karakax fault slip-rate (~2mm/yr), it is smaller than those along the ATF and KF (>9 and >8mm/yr, respectively), yielding a few mm/yr of extension accommodated most likely in the Ashikule graben and surroundings, located between the ATF and Karakax faults. Numerous evidences of recent tectonic-related events are present in the vicinity, such as the 1951 volcanic eruption as well as the 2008 and 2014 Ms7.3 Yutian earthquakes, attesting of its high activity. In addition, the LGCF's en-echelon geometry and identical direction with the ATF, as well as smaller geological offsets and lower slip-rate compared to those on the surrounding faults, suggest that this segment of the ATF may be the most recent.

Western Tibet relief evolution since the Oligo-Miocene

Western Tibet, between the Karakorum fault and the Gozha–Longmu Co fault system, is mostly internally drained and has a 1.5–2km amplitude relief with km-large valleys. We investigate the origin of this peculiar morphology by combining a topography analysis and a study of the Cenozoic sedimentation in this area. Cenozoic continental strata correspond to a proximal, detrital fan deposition, and uncomformably rest on a palaeorelief similar to the modern one. Zircon U–Pb dating from trachytic flows interbedded within the Cenozoic continental sediments indicates that detrital sedimentation occurred at least between ca 24 and 20Ma in the Shiquanhe basin, while K/Ar ages suggest it may have started since ~37Ma in the Zapug basin. The distribution of continental deposits shows that present-day morphology features, including km-large, 1500m-deep valleys, were already formed by Early Miocene times. We suggest that today's internally drained western Tibet was externally drained, at least during late Miocene, contemporaneously with early motion along the Karakorum Fault. Detailed study of the present day river network is compatible with a dextral offset on the Karakorum Fault of 250km at a rate of ~10±1mm/yr. Displacement along the Karakorum fault possibly induced the shift from external to an internal drainage system, by damming of the Bangong Co ~4Ma ago, leading to the isolation and preservation of the western Tibet relief.

Synkinematic magmatism, heterogeneous deformation, and progressive strain localization in a strike‐slip shear zone: The case of the right‐lateral Karakorum fault

New structural observations coupled with 15 U/Pb and 24 Ar/Ar new ages from the Karakorum shear zone (KSZ) constrain the timing and slip rate of the right‐lateral Karakorum fault zone (KFZ), one of the great continental Asian strike‐slip faults. In the Tangtse‐Darbuk area, the Tangtse (SW) and Muglib (NE) mylonitic strands of the KSZ frame the less deformed Pangong Range. Inherited U/Pb ages show that granitic protoliths are mostly from the Karakorum and Ladakh batoliths, with a major Miocene melting event lasting from ≥21.5 to 13.5 Ma. Some of the Miocene granitic bodies show structural evidence for intrusion synkinematic to the KSZ. The oldest of these granitoids is 18.8 ± 0.4 Ma old, implying that deformation started prior to ∼19 Ma. Microstructural data show that right‐lateral deformation pursued during cooling. Ar/Ar data show that ductile deformation stopped earlier in the Tangtse (∼11 Ma) than in the Muglib strand (∼7 Ma). Deformation ended at ∼11 Ma in the Tangtse strand while it is still active in the Muglib strand, suggesting a progressive localization of deformation. When merged with published observations along the KFZ, these data suggest that the KFZ nucleated in the North Ayilari range at least ∼22 Ma ago. The long‐term fault rate is 0.84 to 1.3 cm/yr, considering a total offset of 200 to 240 km. The KSZ collected magma produced within the shear zone and/or deeper in crust for which the producing mechanism stays unclear but was not the lower crustal channel flow.

East–west shortening during north–south convergence, example of the NW Himalayan syntaxis

The northwest terminus of the Himalayan range forms a syntaxis limited by two strike-slip faults, the Chaman Fault to the west, and the Karakorum Fault to the east. In between these faults, smaller-scale syntaxes are observed, as the Nanga Parbat and the Kashmir syntaxes. The fold axial traces of these syntaxes trend nearly north–south, revealing a component of east–west shortening in the geodynamic context of the north–south convergence between India and Asia. We constructed a sandbox with two edges oblique to the convergence to test the influence of the NW Himalayan syntaxis large-scale structural geometry on the construction of a wedge and on its evolution. We used sand and microbeads as standard analogues for brittle crustal layers approximately 30 km thick. We show that the obliquity of the edges can generate an east–west shortening in a north–south convergence. The amount of east–west shortening generated by the oblique edges of the box is up to 40% of the amount of the north–south convergence. This shortening is accommodated by oblique motion on transpressive faults parallel to the edges. The amount of strike-slip motion is up to 60% of the convergence vector. We conclude that the obliquity of the edges is sufficient to generate an east–west shortening in a north–south convergence, but not sufficient to generate a north–south axial-trending fold. One experiment, with a free southern boundary, allowed the development of pure strike-slip faults within the sand layer, conjugated to pure shortening on one north–south fold. The east–west component of the oblique motion generated by the obliquity of the faults bordering the NW Himalayan syntaxis could be absorbed by a north–south fold as the Nanga Parbat if the motion on the border faults is pure strike-slip.

Spatially constant slip rate along the southern segment of the Karakorum fault since 200 ka

Determining the slip-rate history along the right-lateral Karakorum fault (KF) is fundamental to understanding its present-day kinematic role in the deformation of Tibet. Geodetic and geologic studies suggest slip-rates of 0–11mm/yr along this structure. Whether slip-rate variability exists along strike and/or time, or simply results from different measuring techniques/timescales, remains unknown. In order to constrain slip-rates within a timescale of 200ka, we studied fluvial and glacial geomorphic features that are right-laterally or vertically offset by the fault by varying amounts from 7±1m to 430±30m and up to 53±5m, respectively. We constrained their ages using 10Be surface exposure dating on 141 quartz-rich samples collected on 4 lateral moraines and at 3 alluvial sites along the southernmost segment of the KF (Menshi–Kailas basin) and along the Gurla Mandhata detachment fault in the Pulan graben. From the 30° fault bend at Baer (80.5°E) to Mount Kailas area, the slip-rate along the KF is >7.1+3.2/−1.7mm/yr at Menshi and >7.9+3.2/−2.5mm/yr at Kailas (slip on two parallel fault strands). In the Pulan graben, the normal fault slip-rate is >1.6+0.4/−0.3mm/yr. Our data suggest that the Quaternary slip-rate along the southern KF does not decrease eastward but is constant along strike for at least 200km, from >5–11mm/yr in the Gar basin further north to >7–8mm/yr in the Menshi–Kailas basin. Because no expected along-strike slip-rate gradient is observed, it implies that the KF does not end at the Kailas but must extend where the slip rate decreases, i.e. eastward along the Yarlung Zangbo suture and southward along the Gurla Mandhata–Humla fault system.

Fast slip-rate along the northern end of the Karakorum fault system, western Tibet

[1] The exact location of the northern Karakorum fault (KF) in western Tibet is unclear and its current activity is debated. Here, we investigate the possible northern extension of the KF, the Muji fault, located in the Chinese Pamir, which belongs to the Kongur Shan extensional system, and provide the first quantitative estimate of its Holocene slip-rate. The fault cuts and offsets a series of 6 fluvial terraces, yielding a minimum slip-rate of 4.5 ± 0.2 mm/yr, by matching the largest terrace riser offset with its upper surface age (10Be, n = 24). Field evidences of right-lateral movement along the Kongur Shan fault, as well as geometry and kinematic similarities with the southern half of the KF attest that the Muji fault belongs to the KF system. Therefore, its fast slip-rate combined with the slow slip-rates along minor splays of the northern KF (maybe up to 4 mm/yr) southwest of the Tashkorgan basin agrees with the late Pleistocene southern KF slip-rate (>8 mm/yr).

Long‐lasting intracontinental strike‐slip faulting: new evidence from the Karakorum shear zone in the Himalayas

Terra Nova, 23, 92–99, 2011AbstractZircon crystallization ages for a syntectonic granite and an associated dyke along the Tangtse strand of the Karakorum fault are 18.5 ± 0.2 and 18.6 ± 0.2 Ma, respectively. A dyke cross‐cutting the foliation in the Karakorum shear zone (Ksz) yielded an age of 16.0 ± 0.6 Ma. These data show that the Ksz was associated with significant granitic magmatism and was active before 16 Ma, since at least c. 18.5 Ma. Consideration of other data along the Karakorum fault suggests that the fault has most likely been active since c. 22.7–25 Ma at a rate of 8–13 mm a−1. This study conducted in the frontal part of the Himalayan orogen shows that large continental strike‐slip faults can be linked with magmatism and be stable for more than 20 Ma, even in the hottest part of the orogen where strain localization is supposed to be at a minimum.