Evolution of the Deep Structure of Seamounts Viewed from Gravity Anomaly

Abstract

The “depth of compensation” of isostasy was determined for the Maldive Islands and the Chagos archipelago, Indian Ocean. The compensation depth in the region becomes shallow according as the age of the ridge becomes old. The ascending speed of the depth of compensation is about 10km/10ma (1mm/year). To explain the time variation of the depth of compensation, we proposed two models: bubble model and two layers model. In the bubble model, low density material at the deep part of the mantle moves upward. In the two layers model, low density material lies at two layers of different depth and the buoyancy due to these low density material at each depth varies with time, keeping constant the sum of the buoyancy.