The interior of the Earth cools over geological time through the process of thermal convection. Slow creeping flow allows hot material to rise and cold material to sink. This large-scale circulation is responsible for building mountains and driving most of the geological processes we observe at the surface. The Earth also rotates in space, and the orientation of the spin axis evolves slowly with time due to a redistribution of mass associated with thermal convection. Changes in the spin axis, known as true polar wander, are detected in paleomagnetic observations and are attributed to thermal convection. However, it is generally assumed that rotation has little influence on thermal convection. Several new lines of evidence challenge this conventional view. Plate motions are spatially correlated with the orientation of the rotation axis. In addition, the Earth's deep interior has peculiar features that reside on the equator and appear to be affected by rotation. We propose to investigate the dynamic interaction between thermal convection and true polar wander with the aim of better understanding these two fundamental processes.
The proposed research will integrate thermal convection and true polar wander into a single, self-consistent description of planetary dynamics. Numerical models of thermal convection are normally based on a set of equations that describe conservation of mass, heat and linear momentum, whereas models of true polar wander are invariably based on conservation of angular momentum. By expanding and generalizing the usual description of thermal convection, we have combined these two processes into a single set of equations that permit full interaction between convection and true polar wander. We plan to solve these equations numerically by adding new capability to an existing community software package called ASPECT, which was developed with support from NSF. All developments undertaken during this project will be made available to the community through the Computational Infrastructure for Geodynamics (www.geodynamics.org). The software will be useful to other researchers for a wide range of potential applications, including the thermal and chemical evolution of continental lithosphere. The proposed research will also contribute to the training of graduate students and young researchers in advanced computational methods.
