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Abstract

Abstract: The modelling of coupled thermo-kinetic processes associated with non-equilibrium phase change kinetics can be useful for a better understanding of the the time-dependent subduction process. The latent heat release during these non-equilibrium phase changes can dramatically reduce the strength of subducting slabs which would affect their fate. We have investigated the effects of kinetics associated with the olivine-spinel transition in a descending slab. We have laid out the mathematical formulation of a two-dimensional time-dependent model consisting of the kinetic equations, which are cast as a system of nonlinear ordinary differential equations (ODE) at each spatial grid point and the time-dependent partial differential equation (PDE) for the temperature which is coupled to the kinetics by virtue of latent-heat release. This set of ODE-PDE system has been solved by the differential-algebraic method. The structure of the kinetic phase boundary is strongly determined by thermo-kinetic coupling effects during the transition. For slow, warm slabs a localized weakening of the slab could result from the heat production due to the latent heat release. Along the kinetic phase boundary, near the typical depth for equilibrium phase transformations protuberances in the temperature field are obtained caused by the thermal-kinetic feedback inhibiting the transition. Thermal stresses are likely to result from both of these effects. For fast, cold slabs regions with metastable olivine may be pushed down to a depth of about 600 km, while the latent-heat release reduces this effect. Deep focus earthquakes may occur because of the sharp tapering of the metastable phase boundary near 600 km depth. The deep portion of fast subducting slabs may have an anomalously hot and weak region just below the metastable transition wedge. The correlation between slow subducting velocity and the clustering of earthquakes near 400 km depth, e.g. the Izu-Bonin trench, and the fast subducting velocity and the concentration of deep-focus earthquakes at around 600 km depth, as shown for the Tonga-Kermadec trench can be predicted by this 2-D thermal-kinetic model.