Mantle plumes and fingering in the oceanic asthenosphere: evidence from global seismic waveform tomography

Global-scale seismic long period full waveform tomography reveals a pattern of elongated bands of low shear velocity, most prominent between 200-350km depth, below the well-developed low velocity zone. These quasi-periodic finger-like structures of wavelength ~2000 km align parallel to the direction of absolute plate motion for thousands of kilometers. Most prominent in the Pacific Ocean, they are present also in the Indian Ocean and the north and south Atlantic. Below 400 km depth, velocity structure is organized into fewer, undulating but vertically-coherent, low-velocity plumelike features, which appear rooted in the lower mantle, most prominent under Hawaii and the Pacific Superswell. This suggests the presence of a so far unresolved dynamic interplay between plate-driven flow in the low velocity zone and active influx of low rigidity material from deep mantle sources deflected horizontally beneath the moving top boundary layer.