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Title: A review of large low shear velocity provinces and ultra low velocity zones
Award ID(s):
1722623 1664332 1644453
NSF-PAR ID:
10130729
Author(s) / Creator(s):
Date Published:
Journal Name:
Tectonophysics
Volume:
760
Issue:
C
ISSN:
0040-1951
Page Range / eLocation ID:
199 to 220
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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  1. The asthenosphere plays a fundamental role in present-day plate tectonics as its low viscosity controls how convection in the mantle below it is expressed at the Earth’s surface above. The origin of the asthenosphere, including the role of partial melting in reducing its viscosity and facilitating deformation, remains unclear. Here we analysed receiver-function data from globally distributed seismic stations to image the lower reaches of the asthenospheric low-seismic-velocity zone. We present globally widespread evidence for a positive seismic-velocity gradient at depths of ~150 km, which represents the base of a particularly low-velocity zone within the asthenosphere. This boundary is most commonly detected in regions with elevated upper-mantle temperatures and is best modelled as the base of a partially molten layer. The presence of the boundary showed no correlation with radial seismic anisotropy, which represents accumulated mantle strain, indicating that the inferred partial melt has no substantial effect on the large-scale viscosity of the asthenosphere. These results imply the presence of a globally extensive, partially molten zone embedded within the asthenosphere, but that low asthenospheric viscosity is controlled primarily by gradual pressure and temperature variations with depth. 
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