Oceanic crust is generated at mid-ocean ridges by decompression melting of
upwelling mantle at depths of between 50 and 120 km. Geodynamic and geochem
ical models of upwelling, melt extraction, and melt emplacement into crusta
l magma reservoirs present a variety of possible migration geometries, most
of which assume steady-state or near steady-state processes. Here we prese
nt results from marine magnetotelluric (MT) measurements, carried out as pa
rt of the RAMESSES experiment on the slow spreading Reykjanes Ridge, which
support a model of melt extraction and migration that is episodic, rather t
han steady-state.