Abstract

Vertical to subvertical planes of shear within the active crustal deformation field in Tibet align with fast directions of shear-wave polarization. This observation suggests that the present-day velocity gradient tensor field within the crust of Tibet correlates with the lithospheric mantle velocity gradient tensor field beneath Tibet. This inference requires the following. (1) The [100] axes of olivine are aligned within established zones of lithospheric mantle fabric or anisotropy, built up through finite strain. (2) Present-day shear in the mantle lithosphere is occurring within these established zones of fabric, parallel to the direction of olivine [100] axis alignment. (3) The zones of mantle lithospheric fabric, or zones of mantle shear, are aligned with zones of crustal shear (faults). The correlation of crustal and mantle strain fields most simply results from the fact that both crust and mantle lithosphere are under the influence of similar velocity boundary conditions. Furthermore, the observations confirm the distributed nature of lithospheric mantle deformation beneath east-central Tibet and suggest that left-lateral shear has been the dominant component of finite shear there.

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