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TitleAntigorite-induced seismic anisotropy and implications for deformation in subduction zones and the Tibetan Plateau
AuthorShao, T BORCID logo; Ji, S CORCID logo; Kondo, Y; Michibayashi, KORCID logo; Wang, Q; Xu, Z Q; Sun, S S; Marcotte, D; Salisbury, M H
SourceJournal of Geophysical Research, Solid Earth vol. 119, 3, 2014 p. 2068-2099, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20200237
PublisherAmerican Geophysical Union
Mediapaper; on-line; digital
File formatpdf
ProvinceOffshore region
Subjectstectonics; Science and Technology; antigorite; seismic zones; anisotropy; Tibetan Plateau
Illustrationstables; photographs; graphs; histograms; plots; figures; lithologic sections
Released2014 03 24
AbstractThe present study, which is a follow-up of the Journal of Geophysical Research paper by Ji et al. (2013a), provides a new calibration for both seismic and fabric properties of antigorite serpentinites. Comparisons of the laboratory velocities of antigorite serpentinites measured at high pressures with crystallographic-preferred orientation data measured using electron backscatter diffraction techniques demonstrate that seismic anisotropy in high T serpentinite, which is essentially controlled by the antigorite c axis fabric, is independent on the operating slip system but strongly dependent on the regime and magnitude of finite strain experienced by the rock. Extrapolation of the experimental data with both pressure and temperature suggests that V-p anisotropy decreases but shear wave splitting (Delta V-s) and V-p/V-s increase with increasing pressure in either cold or hot subduction zones. For a cold, steeply subducting slab, antigorite is most likely deformed by nearly coaxial flattening or trench-parallel movements, forming trench-parallel seismic anisotropy. For a hot, shallowly subducting slab, however, antigorite is most likely deformed by simple shear or transpression. Trench-normal seismic anisotropy can be observed when the subducting dip angle is smaller than 30 degrees. The geophysical characteristics of the Tibetan Plateau such as strong heterogeneity in Vp, Vs and attenuation, shear wave splitting and electric conductivity may be explained by the presence of strongly deformed serpentinites in lithospheric shear zones reactivated along former suture zones between amalgamated blocks, hydrated zones of subducting lithospheric mantle, and the crust-mantle boundary if the temperature is below 700 degrees C in the region of interest.

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