Tracing the Hawaiian mantle plume by converted seismic waves

Abstract

Hotspots and seamount chains belong to the fundamental components of the global plate tectonics. The Hawaii-Emperor seamount chain is believed to have been created when the oceanic lithosphere continuously passed over a stationary mantle plume located under the Hawaiian islands. Hot buoyant material rises from great depth within a fixed narrow stem to the surface, penetrating the moving lithosphere and creating the volcanic seamounts and islands. We use teleseismic converted waves to look at the seismic velocity anomalies caused by the mantle plume from surface down to depths of the mantle transition zone. We applied the shear-wave (S) receiver function technique to map the thickness of the lithosphere. We found a gradual lithospheric thinning from the island of Hawaii (∼100 km thickness) along the island chain to Kauai (∼60 km thickness) with a width of about 300 km. In this zone our data favour the rejuvenation model, in which the plume returns the lithosphere to conditions close to the ocean ridge. The analysis of the P-to-S converted waves indicates an additional zone of very low S-wave velocity starting at a depth of 130-140 km beneath the central part of the island of Hawaii. We also see in the P-to-S conversions that the upper mantle transition zone is thinned by up to ∼40 km to the southwest of the island of Hawaii. We interpret these observations as localized effects of the Hawaiian plume conduit in the asthenosphere and the mantle transition zone with an excess temperature of 300 °C. The large variation in the transition zone thickness suggests a lower mantle origin of the Hawaiian plume. © 2007 Springer-Verlag Berlin Heidelberg.