Magnetotellurics

As part of the PICASSO project, as well as several related international projects carried out in this area, magnetotelluric (MT) methods have been used to explore the crust and upper mantle beneath the Alboran domain.

Measurements of mantle electrical conductivity are a well known complement to measurements of seismic velocity. Conductivity is sensitive to temperature, composition and hydration of the mantle, and therefore MT is widely used to provide constraints on mantle processes.

Land MT studies have already imaged an area of low resistivity coincident with an area of low velocities without earthquake hypocenters, interpreted as asthenospheric material intruded by the lateral lithospheric tearing and breaking-off of the east-directed subducting Ligurian slab under the Alboran Domain. The model suggests that the most likely scenario for the opening of the Alboran Basin is related to the westward rollback of the Ligurian subducting slab.

Through a series of deployments, we have recovered MT responses from 12 seafloor stations, using a combination of instruments from Geomar and from WHOI. The marine data show complex MT response functions with strong distortion due to seafloor topography and coast effect, suggesting a fairly resistive lithosphere beneath the seafloor. However, initial 3D modeling of the data highlights a zone of low resistivities towards the eastern end of the Alboran domain, consistent with either a hydrous mantle or the presence of a small amount of partial melt. Modeling of the data is ongoing.