A deforming block model for the present-day tectonics of Tibet (original) (raw)
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A kinematic model comprising 14 rotating, elastic-plastic blocks is used to represent the modern deformation of eastern Tibet and neighboring regions. Block rotations, fault slip rates and permanent strain rates within the blocks are constrained by inverting GPS velocities, slip vector azimuths derived from earthquakes, and fault slip rates derived from geology. The calculated internal strain rates of blocks in eastern Tibet amounts to 10 to 30 × 10 −9 /yr, in contrast to relatively low rates (b5×10 −9 /yr) in adjacent blocks including the south China, Alxa and Thailand blocks. F-test statistics show that neither the internal strain rates nor the spins of the blocks can be neglected in describing the surface deformation of eastern Tibet. Furthermore, slip on the main faults verifies that the use of deformable blocks can also predict strain localization and strike-parallel variations in slip rates. In terms of east-southeast motion of the eastern Tibetan plateau relative to the Eurasian plate, the net relative velocity contributed by internal strain rates in the blocks amounts to~10 mm/yr, about half of that due to the faulting. In terms of N-S shortening of plateau, however, the internal strain rises to a first order factor west of 95°E, contributing approximately 10 mm/yr, nearly two times larger than that from faulting. The kinematics in eastern Tibet shows that different types of deformation, i.e., NW-SE shear and N-S compression, are taken up by faulting on major faults and distributed contraction, respectively.
Geological Society, London, Special Publications, 2011
The youngest deformation structures on the Tibet Plateau are about NNE-trending grabens. We first combine remote-sensing structural and geomorphological studies with structural field observations and literature seismological data to study the Muga Purou rift that stretches at c. 86°E across central Tibet and highlight a complex deformation field. ENE-striking faults are dominated by sinistral strike–slip motion; NNE-striking faults have normal kinematics and outline a right-stepping en-echelon array of grabens, also suggesting sinistral strike–slip; along NW-striking fault sets, the arrangement of grabens may indicate a dextral strike–slip component. Thus, in central Tibet, rifts comprise mostly grabens connected to strike–slip fault zones or are arranged en-echelon to accommodate sinistral wrenching; overall strain geometry is constrictional, in which NNE–SSW and subvertical shortening is balanced by WNW–ESE extension. The overwhelmingly shallow earthquakes only locally outline act...
2004
The dextral Karakoram fault zone, that bounds the southwestern margin of Tibet, is widely regarded as one of the major strike-slip faults that accommodates the eastward extrusion of the thickened crust of Tibet. In northern Ladakh, the Karakoram fault bounds the Pangong transpressional zone, with the active fault trace following the eastern margin of the range. Exhumation within this zone reveals mylonites that have absorbed much of the deformation along the fault. Two sets of dikes are evident within the main fault strand that bounds the transpressional zone. Whilst one dike set is concordant with the dominant foliation and shows mylonitic fabric, the youngest dike set are less deformed and cross-cut the shear zone fabric. Using U-Pb ID-TIMS data from five shear zone samples deformed by differing degrees, we infer that fault initiation occurred between 15.68F0.52 and 13.73F0.28 Ma. Since absolute offset is difficult to determine we couple these age constraints with suggested minimum and maximum offsets of the Baltoro-type granites. The offset range of 40-150 km reveals that the Karakoram fault has a longterm average slip-rate in the range 2.7-10.2 mm/year, the lower rate being compatible with GPS, InSAR and cosmogenic data for the fault. The small range of offset and low slip-rates do not support rapid, large-scale extrusion of Tibet along lithosphericscale faults and strengthens the argument that Tibet does not behave in a rigid, plate-like, manner.
Journal of Geodynamics, 1992
Field studies in the Lhasa block (central and eastern S-Tibet, long. 88 ° to 95°E and lat. 29.3 ° to 30°N) demonstrate N-S shortening with coeval and consecutive E-W extension and wrenching. Cretaceous, pre-collisional deformation was both coaxial and non-coaxial with top-to-S displacement in central S-Tibet and top-to-SE displacement in eastern S-Tibet. Post-Eocene, probably Miocene shortening as calculated from restored sections across the Qiuwu molasse and the Xigaze forearc basins caused 1>31% N-S contraction by folding and i>65% by folding, faulting and ductile deformation, with significant coeval E-W extension. Reduced stress tensors calculated from fault-striae data yield ,rl trending subhorizontally 010°(-+15 °) and ira trending subhorizontally 101 ° (___17 °, azimuths of 22 sites in central S-Tibet). 0"2 is tensional.
Earth and Planetary Science Letters, 2018
India-Asia collision analogue modeling Xianshuihe fault Longmen Shan thrust belt Songpan-Ganzi terrane Pre-existing weakness due to repeated tectonic, metamorphic, and magmatic events is a fundamental feature of the continental lithosphere on Earth. Because of this, continental deformation results from a combined effect of boundary conditions imposed by plate tectonic processes and heterogeneous and anisotropic mechanical strength inherited from protracted continental evolution. In this study, we assess how this interaction may have controlled the Cenozoic evolution of the eastern Tibetan plateau during the India-Asia collision. Specifically, we use analogue models to evaluate how the pre-Cenozoic structures may have controlled the location, orientation, and kinematics of the northwest-striking Xianshuihe and northeast-striking Longmen Shan fault zones, the two most dominant Cenozoic structures in eastern Tibet. Our best model indicates that the correct location, trend, and kinematics of the two fault systems can only be generated and maintained if the following conditions are met: (1) the northern part of the Songpan-Ganzi terrane in eastern Tibet has a strong basement whereas its southern part has a weak basement, (2) the northern strong basement consists of two pieces bounded by a crustal-scale weak zone that is expressed by the Triassic development of a northwest-trending antiform exposing middle and lower crustal rocks, and (3) the region was under persistent northeast-southwest compression since ∼35 Ma. Our model makes correct prediction on the sequence of deformation in eastern Tibet; the Longmen Shan right-slip transpressional zone was initiated first as an instantaneous response to the northeast-southwest compression, which is followed by the formation of the Xianshuihe fault about a half way after the exertion of northeast-southwest shortening in the model. The success of our model highlights the importance of pre-existing weakness, a key factor that has been largely neglected in the current geodynamic models of continental deformation.
2010
The role of major strike-slip faults in the Indo-Asian collision zone is central to our understanding of the ways in which continental crust and lithosphere deform in response to continental collision. We investigated how slip varies along the eastern segments of the Kunlun fault in northeastern Tibet. Millennial slip rates were determined based on landforms that are offset by the fault and that were dated using a combination of 14C and cosmogenic radionuclide exposure dating techniques. We developed estimates for slip rates at four new locations along the fault in addition to four previously published sites. All of these sites are located along the eastern 300 km of the fault system, and our results reveal a systematic eastward decrease in slip rate along this portion of the fault since the late Pleistocene. This displacement gradient is consistent with the termination of the Kunlun fault near ~102°E. Coincident variations in fault slip rates and geometry refl ect complex kinematic...
Large-scale geometry, offset and kinematic evolution of the Karakorum fault, Tibet
Earth and Planetary …, 2004
The total offset, lifespan and slip rate of the Karakorum fault zone (KFZ) (western Tibet) are debated. Along the southern fault half, ongoing oblique slip has exhumed dextrally sheared gneisses intruded by synkinematic leucogranites, whose age (V23 Ma, U/Pb on zircon) indicates that right-lateral motion was already in progress in the late Oligocene. Ar/Ar K-feldspar thermochronology confirms that rapid cooling started around 12 Ma, likely at the onset of the present dextral normal slip regime. Correlation of suture zones across the fault requires a total offset greater than 250 km along the active^northern^fault branch. An average long-term slip rate of 1 þ 0.3 cm/yr is inferred assuming that this offset accrued in a time span of 23^34 Ma. Southwest of the Ladakh-Karakorum Range, the large-scale boudinage of ophiolitic units suggests that an offset of several hundreds of kilometers exists along another^southern^branch of the KFZ. Towards the southeast, in the Mount Kailas region, the fault zone does not end at Gurla Mandatha, but continues eastwards, as a transpressive flower structure, along the Indus^Tsangpo suture. Our new data thus suggest that the KFZ contributed to absorb hundreds of kilometers of India^Asia convergence. ß
Geology, 2009
For more than two decades the slip rate along the active, left-slip Altyn Tagh fault of northwestern Tibet has been disputed, with millennial rates reported to be as much as three times faster than those determined geodetically. This problem is signifi cant because the total offset, plate-boundary length, and age of the Altyn Tagh fault make it the most important single structure accommodating India-Asia convergence north of the Himalayas. Here we show that the central Altyn Tagh fault slipped at only 14-9 mm/a over the past 4-6 ka by tightly bracketing the age of a displaced fl uvial terrace riser at Yuemake ). This result contradicts previous latest Quaternary rates and is consistent with those derived from geodetic, paleoseismic, and geologic measurements, and thus resolves the long-standing dispute over the latest Quaternary slip rate along the longest active strike-slip fault in Tibet.
Tectonophysics, 2004
The present-day convergence rate between the Indian and the Eurasian plates has been estimated to be about 50 mm/year. At the collision boundary extending along the Himalayas, about 40% of the total convergence is consumed by the subduction of the Indian plate beneath the Eurasian plate. The rest of about 60% is consumed by the internal deformation of the Eurasian plate. The present crustal movement in this region is characterized by rapid uplift along the high Himalayas and large-scale horizontal deformation in and around Tibet. The fundamental causes of these two different types of crustal movement are the same: interaction between the Indian and the Eurasian plates. In this study we represent the plate interaction by steady increase in tangential displacement discontinuity (dislocation) across the interface that divides a surface layer overlying a viscoelastic half-space into the Indian and the Eurasian plates. First, given a steady slip of 20 mm/year at the plate interface with a ramp-shaped undulation below the high Himalayas, we computed the profile of surface uplift rates along a line perpendicular to the Himalayan arc. The result accords with observed free-air gravity anomalies and the intermediate-and short-term uplift rates estimated, respectively, from the present heights of river terraces and levelling data. This means that the rapid uplift of the high Himalayas is due to the steady slip along the ramp-shaped plate interface below it. Second, given the steady slips of 20 mm/year along the 2000-km-long collision boundary and 50 mm/year along the remaining portions of the India-Eurasia plate boundary, we computed the increase rates of horizontal deformation in and around Tibet. The result accords with the observed strikes and slip rates of major Quaternary active faults. This means that the horizontal deformation in and around Tibet is due to the slip deficits of 30 mm/year at the collision boundary. From these two results we can conclude that the present rapid uplift of the high Himalayas and large-scale horizontal deformation in and around Tibet are consistently explained by a single plate interaction model based on elastic and viscoelastic dislocation theory. This study sheds new light on the driving mechanism of the crustal deformation in the India-Eurasia collision zone as follows. The plate interaction on single plate interface consists of coexisting two different physical mechanisms: (1) slip along the ramp undulation (spatial changes in slip direction), (2) slip deficit at the collision boundary (spatial changes in slip