Numerical Modeling of Transient Thermal Perturbations within the Icelandic Plume

Abstract:

Convection within the Earth's mantle is governed by the Rayleigh number, thought to be in the range of 10⁶-10⁸. Thus mantle convection is predicted to occur in a strongly time-dependent fashion. Regional investigations of the Icelandic plume and the associated V-shaped ridges indicate transient thermal perturbations with amplitudes of 5-30 ^oC. These perturbations occur in a quasi-periodic fashion, with periods of 3-8 million years. As yet, a coherent link between these observations and a dynamic convective model has not been established. In this study, results of numerical models of the Icelandic plume are presented. First, a kinematic advective-diffusive model is used to investigate the surface response caused by thermal perturbations and to determine plume parameter values. Secondly, a fully dynamical investigation is undertaken to derive a mechanism for the production of periodic perturbations. Two-dimensional, axisymmetric, convection models are presented for different Rayleigh numbers. The point at which the system exhibits periodic behaviour is determined and then investigated for different viscosity dependencies. System responses are analysed using boundary layer theory and stability analysis. We find that the relationship between the time period of the periodic thermal perturbation and the Rayleigh number is in agreement with boundary layer theory.