Northward thinning of Tibetan crust revealed by virtual seismic profiles

Tseng, Tai‐Lin; Chen, Wang‐Ping; Nowack, Robert L.

doi:10.1029/2009gl040457

Cited by 100 publications

(80 citation statements)

References 29 publications

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“…Crustal thicknesses beneath stable cratons vary by more than 10-15 km, for instance beneath India [Gupta et al, 2003;Kiselev et al, 2008;Rai et al, 2005], Canada [e.g., Perry et al, 2002], and the Great Plains of the USA [Gilbert, 2012;Sheehan et al, 1995], as well as beneath Tibet [e.g., Tseng et al, 2009]. Again from (2), if uncompensated, such differences in crustal thickness would generate free-air and isostatic gravity anomalies approaching 200-300 mGal.…”

Section: "Residual" Topography and "Dynamic" Topographymentioning

confidence: 99%

Mantle dynamics, isostasy, and the support of high terrain

2015

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Dynamic topography is commonly understood to be deflection of the Earth's surface that results from convection of the mantle. Because different authors use the words "dynamic topography" differently, topography designated as dynamic may amount to only a few hundred meters or may exceed 2000 m. For most regions, however, surface heights computed on the assumption that the lithospheric column is in isostatic equilibrium provide good approximations to observed topography. The small free-air gravity anomalies and still smaller isostatic anomalies (<~30-50 mGal) associated with long-wavelength topography suggest that deflections of the Earth's surface induced by flow-induced normal tractions applied to the base of the lithosphere do not exceed~300 m. Little evidence exists to show that such tractions support more than~100 m of high terrain in regions like southern Africa, the Rocky Mountains and Colorado Plateau of the USA, eastern Asia, or the Aegean-Anatolian region, where some have argued for many hundreds to >2000 m of dynamic topography. Moreover, simple examples show that if flow-induced stresses maintain a given density distribution, then the resultant surface deflections can be smaller than those that would exist in isostatic equilibrium. In light of confusion over the term "dynamic topography," we offer readers simple tools that we hope will enable them to diagnose the component of topography that results from flow-induced stresses and to distinguish it from topography that is compensated isostatically.

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Section: "Residual" Topography and "Dynamic" Topographymentioning

confidence: 99%

Mantle dynamics, isostasy, and the support of high terrain

2015

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“…This is approximately the southern portion of a region in northern Tibet where a number of previous studies have argued for an unusually warm upper mantle, including an unusually thin crust over a regional scale (implying thermal isostasy), and perhaps lateral (E-W trending) flows in the upper mantle, as indicated by very large values (∼2 s) of shear wave birefringence, or even partial melts [Chen et al, 2010;Chen and Özalaybey, 1998;Jiménez-Munt et al, 2008;McNamara et al, 1997;Molnar and Chen, 1984;Ni and Barazangi, 1983;Owens and Zandt, 1997;Tseng et al, 2009].…”

Section: Large-scale Anomalies In the Upper Mantlementioning

confidence: 99%

A data-adaptive, multiscale approach of finite-frequency, traveltime tomography with special reference toPandSwave data from central Tibet

2011

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[1] We discuss an innovation in traveltime tomography that combines wavelet-based, multiscale parameterization and finite-frequency theory to solve two outstanding issues that inevitably arise from uneven source station distributions and from the three-dimensional (3-D) nature of wavefront healing: how to objectively address the intrinsically multiscale nature of data coverage while simultaneously maintain model resolution at each scale level. We apply the new, integrated methodology to investigate 3-D variations of P and S wave speeds (dlnV P and dlnV S ) beneath the Himalayan-Tibetan orogen. In particular, we are able to constrain variations in the Poisson's ratio via dln(V P /V S ). The formulation is naturally data adaptive, resolving features at each scale only if the required data converge is available. The very first, long-wavelength feature that emerges is a clear anomaly of high dlnV that extends over more than 500 km beyond the northern edge of the Lhasa terrane at places. Farther northward, a strong negative anomaly underlies the region where recent volcanism occurs in northern Tibet. Regions of negative dln(V P /V S ) delineate a slab-like, subhorizontal feature concentrated between depths of ∼100-250 km. Such characteristics are consistent with the notion that chemically refractory, and therefore buoyant, mantle lithosphere of the Indian shield ("Greater India") has advanced subhorizontally northward far beyond the surficial Bangong-Nujiang suture. In the crust, two isolated regions of low dlnV, each extending to depths near 100 km, occur along the Lunggar and the Yadong-Gulu active rifts in southern Tibet. Deep penetrating rifts imply that only a limited amount of horizontal displacement is being accommodated on subvertical structures.Citation: Hung, S.-H., W.-P. Chen, and L.-Y. Chiao (2011), A data-adaptive, multiscale approach of finite-frequency, traveltime tomography with special reference to P and S wave data from central Tibet,

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“…This view contrasts with the alternative that the gravitational potential energy of northern Tibet should, in fact, be greater than that of southern Tibet. Crust beneath northern Tibet is thinner by 10-15 km than that beneath southern Tibet [e.g., Owens and Zandt, 1997;Tseng et al, 2009], but elevations are virtually the same. Consequently, the gravitational potential energy per unit area is larger by a few TN/m (10 12 N/m), a difference comparable to that between lithosphere at mid-ocean ridges and at old oceanic lithosphere [e.g., Molnar and Stock, 2009].…”

Section: Introductionmentioning

confidence: 99%

Present‐day crustal thinning in the southern and northern Tibetan Plateau revealed by GPS measurements

Molnár

Shen

et al. 2015

Geophysical Research Letters

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GPS measurements from sites within the Tibetan Plateau show not only east‐southeast‐west‐northwest extension but also, more importantly, horizontal dilation throughout the interior of the plateau. Assuming conservation of volume, vertical (thinning) strain rates equal horizontal dilation rates, and they, 8.9 ± 0.8 nanostrain a−1 and 7.4 ± 1.2 nanostrain a−1 in northern and southern Tibet, and 12.0 ± 3.2 nanostrain a−1 in its southwestern part, suggest no measureable difference. Principal extensional strain rates also are similar in magnitude and orientation. If crustal thinning began at 10–15 Ma and the current rates of horizontal dilation applied both to the entire crust and to that period, the crust should have thinned by 5.5–8.5 km. If isostatic equilibrium applied, the mean elevation of the plateau would have dropped ~1 km. The similar rates for northern, southern, and southwestern Tibet suggest that the processes dictating crustal extension, normal faulting, and crustal thinning in the three regions differ little from one another.

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Northward thinning of Tibetan crust revealed by virtual seismic profiles

Cited by 100 publications

References 29 publications

Mantle dynamics, isostasy, and the support of high terrain

Mantle dynamics, isostasy, and the support of high terrain

A data-adaptive, multiscale approach of finite-frequency, traveltime tomography with special reference toPandSwave data from central Tibet

Present‐day crustal thinning in the southern and northern Tibetan Plateau revealed by GPS measurements

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