SINKING HOT ANOMALY TRAPPED AT THE 410 KM DISCONTINUITY NEAR THE HONSHU SUBDUCTION ZONE, JAPAN

Abstract

A fate of hot anomaly dragged down by subducting slab is studied by simple 2D and 3D fluid dynamical models in which the slab movement is kinematically imposed. The 410 km discontinuity, treated as an olivine-wadsleyite phase change, acts as a barrier to the downward movement of hot anomaly. As a result, the hottest part is located near the 410 km discontinuity. The shape of high temperature anomaly near the 410 km discontinuity is similar to that of the low velocity anomaly under the ocean-ward side of the subduction zone near the Honshu arc, Japan, which was recently convincingly confirmed, and it was interpreted as a mainly thermal anomaly. The time for the hot anomaly to stay near the 410 km discontinuity depends on many factors, such as the intensity of thermal anomalies and the viscosity. We set up a simple model in which such a hot anomaly was produced in the area of the Pacific superplume region and carried toward the Japanese Islands by the horizontal flow associated with the plate movement. The hot anomaly whose size is equivalent to 2-3000 km (horizontal) × 200 km (vertical) may stay there longer than ~ 100 million yr. We will discuss the implication of this result in terms of the relation between the present high temperature anomaly near the Honshu subduction zone and the past activity of the Pacific superplume. © 2007 Elsevier B.V. All rights reserved.