2 December, 2009 (16:00 GMT), 5 Merrion Square, Dublin 2.

Speaker: Rob Evans, Woods Hole Oceanographic Institution, USA.
Title: Magnetotellurics at Subduction Zones: Constraints on Water Inputs and Melt Outputs.

Abstract:

Subduction zones occur where one tectonic plate is pushed below another, either continental or oceanic, and plunges deep into the mantle. The results of this process include substantial volcanism and large earthquakes, making subduction settings probably the most hazardous on Earth. Known unknowns on the process include: the fluxes of water into the system, which plays a critical role in triggering melting of the mantle; the amounts and distribution of melt in the mantle above the downgoing slab; and the delivery of melt to the volcanic, and in some oceanic collisional cases, back-arc spreading center. The Magnetotelluric (MT) method, which measures mantle electrical conductivity, is known to be sensitive to the presence of fluids such as water and melt. I will discuss the role of MT in subduction zone studies ongoing and upcoming. This discussion will include results from a seafloor survey across the Marianas trench and arc, some preliminary land MT work across the Cascadia system in the Northwestern US, and an overview of an upcoming experiment offshore Nicaragua and Costa Rica.