Lithosphere and asthenosphere interactions beneath Hawaii: The SWELL experiment

(G.S. Heinson, A.White and S.C. Constable [Scripps Institution of Oceanography, USA])

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The Hawaiian hot-spot swell represents the surface expression of a plume of melt moving up from the core-mantle boundary, approximately 3000 km below the Earth's surface. The plume is a stationary feature that produces a line of volcanic islands as the Pacific Plate moves. Molten rock pools at the base of the lithosphere, about 100 km down, in a zone 2000 km wide, and is then focussed to a narrow zone of surface eruption.

A magnetotelluric instrument being assembled for deployment on deck of R/V Moana Wave. The magnetometers in the instrument package were developed by FIAMS

These processes are not well understood. In April 1997 we deployed eight seismometers and eight magnetotelluric (MT) instruments from the US ship R/V Moana Wave. The MT instruments were a combination of Scripps Institution electric field loggers and magnetometers made at Flinders University. These sixteen instruments were deployed at distances ranging from 100 km to over 700 km from the main Hawaiian island, in a circular pattern to constrain two and three-dimensional structure in the lithosphere-asthenosphere. Water depths ranged from 4300 m to 5600 m.

The recovery cruise took place in December 1997 from the R/V Moana Wave. All instruments were recovered and gave good data. Processing is in progress, but initial two-dimensional inversions show a low resistivity rise beneath the Hawaiian swell, consistent with a pool of melt at a depth of 100 km.

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