Abstract

A growing compilation of active and passive-source seismic surveys reveal a transition across oceanic lithospheric plates that is sharp, sometimes anisotropic, and often marked by complex anisotropic layering underneath hotspot islands. A simple view of ocean plate formation and evolution where thermal cooling governs with only a confined role for intermittent hotspot/plume activity is challenged by these new seismic constraints. In this presentation, I discuss how new seismic constraints, i.e., attenuation and age-dependence of a sharp low-velocity zone, lend support to a subsolidus elastically accommodated grain-boundary sliding (EAGBS) model. We propose that this is the cause of the sharp seismic low-velocity transition often referred to as the lithosphere-asthenosphere boundary (i.e. the underside of the oceanic plate). The EAGBS does not facilitate long-term ductile deformation, so the sharp seismic boundary may not coincide with the conventional transition from lithosphere to asthenosphere corresponding to a change in the long-term rheological properties.

This seminar will be held online. Zoom details will be sent to members of the Earth Sciences department via email. Please contact the organisers if you are outside the department and would like to attend.