Geodynamic Significance of Seismic Anisotropy of the Upper Mantle: New Insights from Laboratory Studies

TLDR

Seismic anisotropy arises mainly from lattice‑preferred orientation of anisotropic minerals, with recent large‑strain, high‑pressure olivine experiments revealing key insights, yet uncertainties remain about pressure effects and low‑stress deformation fabrics. The study examines how water, stress, temperature, pressure, and partial melting influence lattice‑preferred orientation. Water has a large influence, requiring major revisions to the geodynamic interpretation of seismic anisotropy in tectonically active regions, while partial melting affects deformation fabrics mainly through water redistribution, and combined experimental and seismological data illuminate water distribution in plume‑asthenosphere interactions, oceanic lithosphere formation, and subduction.

Abstract

Seismic anisotropy is caused mainly by the lattice-preferred orientation of anisotropic minerals. Major breakthroughs have occurred in the study of lattice-preferred orientation in olivine during the past ∼10 years through large-strain, shear deformation experiments at high pressures. The role of water as well as stress, temperature, pressure, and partial melting has been addressed. The influence of water is large, and new results require major modifications to the geodynamic interpretation of seismic anisotropy in tectonically active regions such as subduction zones, asthenosphere, and plumes. The main effect of partial melting on deformation fabrics is through the redistribution of water, not through a change in deformation geometry. A combination of new experimental results with seismological observations provides new insights into the distribution of water associated with plume-asthenosphere interactions, formation of the oceanic lithosphere, and subduction. However, large uncertainties remain regarding the role of pressure and the deformation fabrics at low stress conditions.