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DDC:
550 - Earth sciences
Abstract:
The volcanic edifice of the Hawaiian islands and seamounts, as well as the surrounding area of shallow sea floor known as the Hawaiian swell, are believed to result from the passage of the oceanic lithosphere over a mantle hotspot1-3. Although geochemical and gravity observations indicate the existence of a mantle thermal plume beneath Hawaii4-6, no direct seismic evidence for such a plume in the upper mantle has yet been found. Here we present an analysis of compressional-to-shear (P-to-S) converted seismic phases, recorded on seismograph stations on the Hawaiian islands, that indicate a zone of very low shear-wave velocity (< 4km s-1) starting at 130-140 km depth beneath the central part of the island of Hawaii and extending deeper into the upper mantle. We also find that the upper-mantle transition zone (410-660 km depth) appears to be thinned by up to 40-50 km to observations as localized effects of the Hawaiian plume conduit in the asthenosphere and mantle transition zone with excess temperature of ~300°C. Large variations in the transition-zone thickness suggest al lower-mantle origin of the Hawaiian plume similar to the Iceland plume7, but our results indicate a 100°C higher temperature for the Hawaiian plume.
