Seismic evidence for a mantle plume oceanwards of the Kamchatka-Aleutian trench junction

Abstract

A non-linear iterative P-wave traveltime tomography has revealed a mantle plume originating at a depth of nearly 1000 km, rising across the 600 km discontinuity, and deflecting subhorizontally in the uppermost mantle presumably by shear flow due to the overlying moving plate. Data from the Geophysical Survey of Russia (1955-1997) were inverted jointly with the catalogues of International Seismological Centre and USGS National Earthquake Information Centre (1964-1998). The result shows a 300-500 km-wide cylindrical low-velocity anomaly (∼ - 2 per cent) that extends from a depth of greater than 900 km to shallower than 200 km. The anomaly is almost vertical at depths up to ∼400 km and rises obliquely to the north up to ∼200 km under the ocean floor near the northern end of Emperor seamounts. Above ∼300 km depth a subsidiary anomaly extends subhorizontally to the NW in fair agreement with the direction of movement of the Pacific Plate. The overlying seafloor is characterized by anomalously high heat flow, which may be attributed to the thermal effect of the mantle plume.