Influence of Rheology on the Lengthscale of Mantle Convection

In the debate of whole vs. layered mantle convection much attention has been paid to the vertical extent of convection planforms. Closely connected and potentially equally important in this discussion is the horizontal lengthscale of mantle convection. Studies that have addressed the horizontal lengthscale of mantle convection have found that prescribing a shallow low viscosity channel in convection models can be crucial for promoting long wavelength flow. However, work involving self-consistent mantle models, in which viscosity is a function of temperature, depth, and yield stress, have not readily observed long horizontal wavelengths. In this work, rather than prescribing a low viscosity channel, we generate one in numerical mantle convection models by using a temperature and pressure dependent rheology. We explore which rheologic ingredients are necessary for a shallow low viscosity channel to develop, and which degree of "channeliness" facilitates long wavelength convection and plate-like motion. Our numerical experiments may help constrain which mode of mantle convection is dominant in Earth's mantle.