Deformation-related electrical conduction mechanisms at the lithosphere-asthenosphere boundary below Australia
The motion of tectonic plates over the underlying mantle – or asthenosphere – leads to strain-induced alignment of mantle minerals such as olivine. Crystallographic alignment of olivine is hypothesised to cause electrical anisotropy due to faster diffusion of trace amounts of H+ ions along the a-axis of olivine crystals than along other axes. The few ppm water required for this mechanism to operate should significantly affect the viscosity of the asthenosphere.
In this talk, I will use magnetotelluric (MT) and geomagnetic depth sounding (GDS) data from Australia to explore a) the relationship between plate motion, mantle flow, electrical conductivity, rheology and trace amounts of water in the Earth’s mantle; b) the ambiguous nature of the lithosphere-asthenosphere boundary and how we define it in relationship to plate thickness; c) the possibility of using electrical conductivity data to constrain the water content and therefore viscosity of the asthenosphere below West Australia in a bid to explain how the Yilgarn craton has resisted tectonically-driven recycling into Earth’s interior for billions of years.