Mantle convection, the asthenosphere, and Earth's thermal history

Abstract

Calculations of mantle convection generally use constant rates of internal heating and uniform core-mantle boundary temperature while thermal history calculations allow these properties to vary with time but only provide an average mantle temperature. Here I consider 3D spherical convection calculations that run for the age of the Earth with heat producing elements that decrease with time, a cooling core boundary condition, and a mobile lid. The mantle temperature cools with time from a moderately hot initial temperature. I find that the mobile versus stagnant lid has the most significant effect on the average temperature as a function of time in the models, but the lithosphere has less of an effect on the planform, or pattern of hot and cold anomalies. I find the same low-degree (one upwelling or two upwelling) patterns of temperature anomalies with a mobile lid that have previously been found in stagnant-lid calculations. While having less of an effect on the mean mantle temperature, the viscosity of the asthenosphere has a profound effect on the pattern of temperature anomalies, even in the deep mantle. If the asthenosphere is weaker than the upper mantle by more than an order of magnitude, then the low degree (one or two giant upwellings) structure results. If the asthenosphere is less than an order of magnitude weaker than the upper mantle, then the planform has narrow cylindrical upwellings and