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 1000km, 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 300-500km-wide cylindrical low-velocity anomaly (~-2 per cent) that extends from a depth of greater than 900km to shallower than 200km. The anomaly is almost vertical at depths up to ~400km and rises obliquely to the north up to ~200km under the ocean floor near the northern end of Emperor seamounts. Above ~300km 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.