A Dynamic Lithosphere-Asthenosphere Boundary beneath Middle Atlantic Ridge

Ocean ridges have a simpler history than the continents and thus provide a good laboratory to study the plate tectonics, partial melts, etc. The most obvious manifestations of tectonic activities on Earth, such as earthquakes and volcanoes, occur near the plate boundaries. Therefore, these activities are used to study the boundaries through seismology. However, the differential motion at the lithosphere-asthenosphere boundary (LAB) is aseismic, and the ocean ridges, as the divergent tectonic plate boundaries, are not as seismically active as the continental plate boundaries. Meanwhile, upwelling magma/melts at the ocean ridges and the partially molten LAB are ten times more electrically conductive than their surrounding rocks, and thus are ideal targets for magnetotellurics (MT). Therefore, marine MT is used to study Earth’s deep interior beneath middle Atlantic ridge (MAR). We developed electrical resistivity models beneath MAR and reconstructed electrical LAB with MT data by inverse modelling through the iLAB project. Our resistivities models, showing patched and channeling partial melts, have a good agreement with share-wave velocity models driven by surface wave tomography. The resistivity models together with the velocity models show a more dynamic LAB than previously thought, which enriches the understanding of LAB, partial melts, and melt fraction beneath the ocean ridges.