Shear-wave splitting and small-scale convection in the continental upper mantle

Makeyeva, Larissa; Vinnik, Lev; Roecker, S. W.

doi:10.1038/358144a0

Cited by 129 publications

(79 citation statements)

References 15 publications

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“…One is in the low Pn velocity zone in south central Tien Shan; the other is the high Pn velocity zone in north central Tien Shan and the south edge of Kazakh platform. The fast Pn directions are mostly near north-south direction in south central Tien Shan, perpendicular to the mountain belts, and are consistent with the SKS fast direction [4,5] , which means the material flow promoted by mantle upwelling had affected the uppermost mantle; In the north central Tien Shan and the south edge of Kazakh platform, the fast Pn directions circumrotate around the high velocity zone, with large amplitude of anisotropy. According to the SKS splitting studies [4,5] , the fast directions in north central Tien Shan were mostly in east-west direction, parallel to the mountain belts, which means the anisotropy patterns were different between uppermost mantle and deep upper mantle.…”

Section: Fig 5 Pn Velocity Structure and Earthquake Locationssupporting

confidence: 65%

PN Wave Velocity Structure and Anisotropy in the Central Tien Shan Region

Roecker

et al. 2007

Chinese J of Geophysics

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Pn wave velocity structure and anisotropy in the central Tien Shan are inversed by using seismic arrival data from the broadband temporary network (GHENGIS) and the Kyrgyzstan seismic network (KNET). Results reveal lower average Pn velocities and a strong heterogeneity at the uppermost mantle beneath the central Tien Shan, which are often found in tectonically active zones. Particularly, very low Pn velocities are found in the south-central Tien Shan, which is believed to be underlain by an unusual mantle with higher heat flows. There is a clear correlation between seismic activity and Pn velocity variation. Most earthquakes are concentrated in the north-central Tien Shan with hight Pn velocities, while almost no earthquakes located in the south-central Tien Shan with very low Pn velocities. Our result suggests that the very low Pn velocity beneath the southcentral Tien Shan is caused by high temperatures produced by heating from mantle upwelling, and that this heat has been conducted well up into the crust, inducing a ductile rheology that prevents significant seismic activity. Moreover, strong anisotropy is observed in the north-and south-central Tien Shan. Fast Pn velocity anisotropy in the south-central Tien Shan is nearly in N-S directions, which is consistent with the SKS wave anisotropy concerning mantle flow. However, fast Pn velocity directions in the north-central Tien Shan show a southward rotation variation. We estimate that it is probably related to the inserting of the crust of the Chu basin from the southern Kazakstan platform to the central Tien Shan, which caused a change of stress fields and lithosphere deformation.

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Section: Fig 5 Pn Velocity Structure and Earthquake Locationssupporting

confidence: 65%

PN Wave Velocity Structure and Anisotropy in the Central Tien Shan Region

Roecker

et al. 2007

Chinese J of Geophysics

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“…The circular pattern surrounding a central region of null measurements is suggestive of regional-scale asthenospheric flow. Such small-scale convection has been suggested for the upper mantle beneath the Tien Shan in central Asia [Makeyeva et al, 1992]. The splitting polarizations at the northern and southern edges of the study region are close to the absolute plate motion direction, as expected for asthenospheric flow beneath the lithosphere [e.g., Leven et al, 1981 ].…”

Section: Modelsmentioning

confidence: 96%

Seismic anisotropy and mantle flow from the Great Basin to the Great Plains, western United States

Savage¹,

Sheehan²

2000

J. Geophys. Res.

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“…2). This estimate is based on the assumption of ductile rheology of the lower crust, which is supported for this area by multiple data starting from seismic data (Vinnik and Saipbekova, 1984;Makeyeva, 1992;Roecker et al, 1993;Vinnik et al, 2006) and ending by gravity-flexural analysis (Burov et al, 1990(Burov et al, , 1993Avouac and Burov, 1996). Only short topographic wavelengths, typically less than a few tens of kilometres that can be supported by the strength of the upper crust, would be maintained over geological periods of time, yet provided that they are not removed by erosion (which is faster on short wavelength topography).…”

Section: Introductionmentioning

confidence: 99%

Thermo-Mechanical Models for Coupled Lithosphere-Surface Processes: Applications to Continental Convergence and Mountain Building Processes

Burov

2009

New Frontiers in Integrated Solid Earth Sciences

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Simple mechanical considerations show that many tectonic-scale surface constructions, such as mountain ranges that exceed certain critical height (about 3 km in altitude, depending on rheology and width) should flatten and collapse within few My as a result of gravitational spreading that may be enhanced by flow in the ductile part of the crust. The elevated topography is also attacked by surface erosion that, in case of static topography, would lead to its exponential decay on a time scale of less than 2.5 My. However, in nature, mountains or rift flanks grow and stay as localized tectonic features over geologically important periods of time (>10 My). To explain the long-term persistence and localized growth of, in particular, mountain belts, a number of workers have emphasized the importance of dynamic feedbacks between surface processes and tectonic evolution. Surface processes modify topography and redistribute tectonically significant volumes of sedimentary material, which acts as vertical loading over large horizontal distances. This results in dynamic loading and unloading of the underlying crust and mantle lithosphere, whereas topographic contrasts are required to set up erosion and sedimentation processes. Tectonics therefore could be a forcing factor of surface processes and vice versa. One can suggest that the feedbacks between tectonic and surface processes are realised via 2 interdependent mechanisms: (1) slope, curvature and height dependence of the erosion/deposition rates; (2) surface load-dependent subsurface processes such as isostatic rebound and lat-E. Burov ( ) University Paris VI, Case 129, 4 Place Jussieu, Paris 75252, France e-mail: evgenii.burov@upmc.fr eral ductile flow in the lower or intermediate crustal channel. Loading/unloading of the surface due to surface processes results in lateral pressure gradients, that, together with low viscosity of the ductile crust, may permit rapid relocation of the matter both in horizontal and vertical direction (upward/downward flow in the ductile crust). In this paper, we overview a number of coupled models of surface and tectonic processes, with a particular focus on 3 representative cases: (1) slow convergence and erosion rates (Western Alpes), (2) intermediate rates (Tien Shan, Central Asia), and (3) fast convergence and erosion rates (Himalaya, Central Asia).

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Shear-wave splitting and small-scale convection in the continental upper mantle

Cited by 129 publications

References 15 publications

PN Wave Velocity Structure and Anisotropy in the Central Tien Shan Region

PN Wave Velocity Structure and Anisotropy in the Central Tien Shan Region

Seismic anisotropy and mantle flow from the Great Basin to the Great Plains, western United States

Thermo-Mechanical Models for Coupled Lithosphere-Surface Processes: Applications to Continental Convergence and Mountain Building Processes

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