Inferring upper-mantle flow from seismic anisotropy: An experimental perspective

Patterns of mantle flow are most directly inferred from observations of seismic anisotropy, which is mainly caused by the crystallographic preferred orientation (CPO) of olivine, the most abundant mineral in the upper mantle. CPO is generated by high temperature ductile deformation, which often yields predictable relationships between the elastic or seismic properties of a material and the kinematics of flow. Over the last 15 years there has been a wealth of new data describing the how olivine CPO forms and evolves as a function of deformation conditions and strain magnitude. In this review, we explore the relationships between deformation, the evolution of CPO, and the development of seismic anisotropy, from the perspective of experimental rock mechanics. We first review the experimental basis for the study of olivine CPO evolution from the formative studies in the early nineteen sixties through recent advances. We then review some emerging complications to the study of CPO evolution, such as the long-lived transient CPOs that arise from changes in deformation kinematics, mechanisms, and conditions. Finally we discuss the origins of seismic anisotropy and the challenges of interpreting seismic anisotropy in terms of mantle flow.