Anisotropic regime across northeastern Tibet and its geodynamic implications

Ye, Zhuo; Li, Qiusheng; Gao, Rui; Zhang, Hongshuang; Shen, Xuzhang; Liu, Xuzhou; Gong, Chen

doi:10.1016/j.tecto.2016.01.011

Cited by 27 publications

(15 citation statements)

References 45 publications

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“…First, the topography is flat in both the eastern part of Qilian Orogen and the Yinshan Block (Figure ) [ Guo et al , ], without “flower structures” or fold developments suggested by Meyer et al [], differing from the numerical simulation conclusions that the intracontinental convergence with various initial conditions all lead to high topography over the contacting zone [ Chen et al , ]. Second, to reconcile the previous southward subduction and the present‐day east‐west relative slip between the orogen and the block, crust‐mantle decoupling is required [ Ye et al , ; Guo et al , ]. However, neither the surface wave anisotropic tomography [ Pandey et al , ; Shen et al , ] nor the joint analysis of shear wave splitting and GPS data [ Wang et al , ; Chang et al , ] could support such decoupling in our study area.…”

Section: Discussionmentioning

confidence: 99%

Limited southward underthrusting of the Asian lithosphere and material extrusion beneath the northeastern margin of Tibet, inferred from teleseismic Rayleigh wave tomography

et al. 2017

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The northeastern margin of Tibet is of key importance in understanding the uplift and expansion of Tibetan Plateau. In this research, we perform Rayleigh wave tomography from 20 s to 167 s using the data recorded by China Digital Seismic Network and several portable seismic arrays in Northeastern Tibet and adjacent areas. Our resultant 3‐D shear wave velocity model exhibits strong lateral variations in the lithosphere. High shear wave velocities are observed in the mantle of the cratonic Ordos and Yangtze Blocks, as well as the East Qinling Orogen. The Qilian Orogen is underlain by a ∼120 km thick lithosphere of intermediate velocities and a low‐velocity layer of asthenospheric mantle below the depth of 120 km. Low velocities are characteristic in the middle‐to‐lower crust of the Songpan‐Ganzi Terrane and the West Qinling Orogen, possibly representing the crustal flow penetrating the Kunlun Fault. An uppermost mantle low‐velocity zone is found in the same location, indicating either the asthenosphere upwelling or the transitional crust‐mantle boundary layer. Our observations have two tectonic implications. First, the large‐scale eastward Tibetan material extrusion into Eastern China through the East Qinling Orogen is unlikely to be an ongoing process above 200 km depth; second, the southward subduction of the North China Craton toward Northeastern Tibet may not have fully developed in this region. Furthermore, we propose that the difference in the lithospheric strength between the Qaidam Block and the West Qinling Orogen is a critical element to control the tectonics in the northeastern margin of Tibet.

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Section: Discussionmentioning

confidence: 99%

Limited southward underthrusting of the Asian lithosphere and material extrusion beneath the northeastern margin of Tibet, inferred from teleseismic Rayleigh wave tomography

et al. 2017

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“…In addition to the lateral variations as described above, the shear-wave splitting 246 measurements at many stations show notable azimuthal variations. Previous studies 247 argued that the azimuthal variations can be explained by a two-layer anisotropy model 248 under West Qinling (Li et al, 2011;Ye et al, 2016). Here, we fit the shear-wave 249 splitting measurements with two-layer models in moving spatial windows (fixed to 250 grid nodes), as there is an insufficient number of measurements at individual stations.…”

Section: Two-layer Anisotropy 245mentioning

confidence: 99%

Insight into NE Tibetan Plateau expansion from crustal and upper mantle anisotropy revealed by shear-wave splitting

Huang

Tilmann

et al. 2017

Earth and Planetary Science Letters

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The northeastern Tibetan plateau margin is the current expansion border, where growth of the plateau is ongoing. We analysed shear-wave splitting at ChinArray stations in the NE Tibetan Plateau and its margin with the stable North Chine Craton. The measurements provide important information on the seismic anisotropy and deformation patterns in the crust and upper mantle, which can be used to constrain the expansion mechanism of the plateau. Along the margin and within the craton, the dominant NW-SE fast polarization direction (FPD) is NW-SE, subparallel to the boundary between the plateau and the North China Craton. The shear-wave splitting measurements on the NE Tibetan Plateau itself generally reflect a two-layer anisotropy. The lower-layer anisotropy (with NW-SE FPDs) is consistent in the whole region, and FPDs are the same as those in the North China Craton. The upper-layer FPDs are parallel to the boundary orogens and faults along the NE Tibetan Plateau margin and are parallel to crustal motion rather than surface structures within the high plateau. The two-layer anisotropy implies the presence of deformed Tibetan lithosphere above the underthrusting North China Craton. The NE Tibetan Plateau shows similar deformation patterns at the surface (inferred from GPS) and within the mantle (inferred from shear-wave splitting), but significant crustal anisotropy (parallel to crustal motion) requires midlower crustal channel flow or detachment to drive further tectonic uplift of the plateau.

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“…The presence of substantial azimuthal anisotropy beneath Tibet is well established in studies using different techniques and data types, including surface-wave imaging (e.g., Griot et al 1998;Huang et al 2004;Su et al 2008;Yao et al 2010;Yi et al 2010;Yang et al 2010b;Ceylan et al 2012;Legendre et al 2015;Pandey et al 2015;Schaeffer et al 2016;Xie et al 2016;Chen et al 2016), shear-wave splitting analysis (e.g., McNamara et al 1994;Hirn et al 1995;Sandvol et al 1997;Sol et al 2007;Zhao et al 2010;Leon Soto et al 2012;Eken et al 2013;Chang et al 2015;Wu et al 2015a;Chen et al 2015;Liu et al 2016;Singh et al 2016;Ye et al 2016), receiver functions (e.g., Vergne et al 2003;Levin et al 2008;Shen et al 2015;Liu et al 2015;Kong et al 2016), attenuation studies (Bao et al 2012) and P-wave arrival times (e.g., Wei et al 2013;Huang et al 2014;Zhang et al 2016b;Wei et al 2016). Radial anisotropy (the difference between the vertically and horizontally polarized waves: V SV and V SH , respectively, in the case of S waves) is also well documented (e.g., Shapiro et al 2004;Huang et al 2010;Duret et al 2010;Guo et al 2012;Xie et al 2013;Li et al 2016).…”

Section: Azimuthal and Radial Anisotropy Beneath Tibet: A Brief Synthmentioning

confidence: 99%

“…Two-layer modelling of shear-wave splitting has also been carried out at a number of other sites within the plateau (Levin et al 2008;Huang et al 2011;Li et al 2011;Levin et al 2012;Wu et al 2015b;Ye et al 2016). …”

Section: Origin Of Shear-wave Splitting Beneath Tibetmentioning

confidence: 99%

Complex, multilayered azimuthal anisotropy beneath Tibet: evidence for co-existing channel flow and pure-shear crustal thickening

Agius

Lebedev²

2017

Geophysical Journal International

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SUMMARYOf the two debated, end-member models for the late-Cenozoic thickening of Tibetan crust, one invokes "channel flow" (rapid viscous flow of the mid-lower crust, driven by topography-induced pressure gradients and transporting crustal rocks eastward) and the other-"pure shear" (faulting and folding in the upper crust, with viscous shortening in the mid-lower crust). Deep-crustal deformation implied by each model is different and would produce different anisotropic rock fabric. Observations of seismic anisotropy can thus offer a discriminant. We use broadband phase-velocity curves-each a robust average of tens to hundreds of measurements-to determine azimuthal anisotropy in the entire lithosphere-asthenosphere depth range and constrain its amplitude. Inversions of the differential dispersion from path pairs, region-average inversions and phase-velocity tomography yield mutually consistent results, defining two highly anisotropic layers with different fast-propagation directions within each: the middle crust and the asthenosphere.In the asthenosphere beneath central and eastern Tibet, anisotropy is 2-4 per cent and has a NNE-SSW fast-propagation azimuth, indicating flow probably driven by the NNEward, shallow-angle subduction of India. The distribution and complexity of published shear-wave splitting measurements can be accounted for by the different anisotropy in the mid-lower crust and asthenosphere. The estimated splitting times that would be ac-2 M.R. Agius and S. Lebedev cumulated in the crust alone are 0.25-0.8 s; in the upper mantle-0.5-1.2 s, depending on location. In the middle crust (20-45 km depth) beneath southern and central Tibet, azimuthal anisotropy is 3-5 and 4-6 per cent, respectively, and its E-W fast-propagation directions are parallel to the current extension at the surface. The rate of the extension is relatively low, however, whereas the large radial anisotropy observed in the middle crust requires strong alignment of mica crystals, implying large finite strain and consistent with high-rate horizontal flow. Together, radial and azimuthal anisotropy suggest eastward mid-crustal channel flow in central Tibet, along the regional topography gradient.In NE high Tibet, mid-crustal azimuthal anisotropy is 4-8 per cent and has WNW-ESE and NW-SE fast-propagation directions, parallel to the net extension at the surface. These fast directions are inconsistent with channel flow following the SW-NE regional topography gradient. Instead, they suggest similar net deformation in the (decoupled) shallow and deep crust. In the brittle upper crust, it is accommodated by strike-slip faulting; in the ductile mid-lower crust-by shear oriented at ∼45 • to the faults. Although mid-crustal flow beneath NE Tibet may transport some material towards the plateau periphery at a low region-average rate, the dominant mid-crust deformation pattern is shear parallel to the plateau boundary. This implies that channel flow from central Tibet is not the main cause of the on-going crustal thickening farther northeast.

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Anisotropic regime across northeastern Tibet and its geodynamic implications

Cited by 27 publications

References 45 publications

Limited southward underthrusting of the Asian lithosphere and material extrusion beneath the northeastern margin of Tibet, inferred from teleseismic Rayleigh wave tomography

Limited southward underthrusting of the Asian lithosphere and material extrusion beneath the northeastern margin of Tibet, inferred from teleseismic Rayleigh wave tomography

Insight into NE Tibetan Plateau expansion from crustal and upper mantle anisotropy revealed by shear-wave splitting

Complex, multilayered azimuthal anisotropy beneath Tibet: evidence for co-existing channel flow and pure-shear crustal thickening

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