Azimuthal anisotropy and phase velocity beneath Iceland: implication for plume-ridge interaction

摘要

We have determined the patterns of azimuthal anisotropy beneath Iceland from shears-wave splitting and Rayleigh wave tomography using seismic data recorded during the ICEMELT and HOTSPOT experiments. The fast directions of shear-wave splitting are roughly N-S in western Iceland and NNW-SSE in eastern Iceland. In western Iceland azimuthal variations in Rayeight wave phase velocity show that fast directions are close to the plate spreading direction a short periods of 25-40 s and roughly parallel to the Mid-Atlantic Ridge at longer periods of 50-67 s indicates that the lowest velocities are beneath the rift zones in central Iceland rather than above the plume conduit in southeast iceland. While ridge-parallel alignment of melt fails might contribute to anisotropy above 50 km depth beneath the rift zones, the overall observations are consistent with a model in which plume-influenced, hot, buoyant mantle rises beneath the Mid-Atlantic Ridge at depths greater than 50 km and is preferentially channeled along the ridge axis at the base of th lithosphere beneath Iceland. The shear-wave splitting results are attributed primarily to a N-S mantle flow at depths greater than 100 km.