Thermal regime of a downgoing slab and new global tectonics

Abstract

The new global tectonics and sea-floor spreading hypotheses imply downwarping and descent of the lithosphere in island-arc regions. These downgoing slabs of crust and upper-mantle material will affect the local temperature regime. Geophysically observable variables of surface-heat flux and gravity and seismic travel times will be influenced by the temperature. Using a quasi-dynamic computational scheme and a finite difference solution of the conservation of energy equation we have determined the effects of spreading rate, adiabatic compression, radioactivity, phase changes, and strain heating on the temperature regime of a downgoing slab. Effects of these parameters on surface heat flux, gravity anomalies, and local seismic travel time are also estimated. Predicted travel-time anomalies show good agreement with observed anomalies in Japan and Tonga-Kermadec. Several implications on the localized mechanical behavior of the upper mantle and the evolution of a downwarping slab are made on the basis of our computational results.