OCGC Seminar - Mantle convection with strong plates


Mantle convection with strong plates:
multiple solutions, hysteresis, and the dynamic state of a planet


Dr. John Crowley
Canadian Geodetic Survey, Natural Resources Canada


Thursday, December 3rd, 2015
11:30 a.m.  

Gamble Hall
615 Booth Street



Plate tectonics regulates the thermal and chemical state of a planet and may be a necessary condition for a stable surface environment and a habitable planet. Predicting the rate at which tectonic plates move is crucial for understanding both the thermal and chemical evolution of a planet.

A new boundary layer model for thermal convection with finite-strength plates and depth-dependent viscosity has been developed. The model permits solutions in which convective flow rates in the mantle may exceed the plate velocity. Multiple solutions are found with three solution branches for the plate velocity representing three distinct modes of thermal convection. All three modes emerge naturally from the simple energy balance model and have varying degrees of plate-mantle coupling, as well as different dominant plate driving forces. The branch of solutions with the largest plate velocity reproduces the classic convective scaling laws for thermal convection in an iso-viscous fluid (Turcotte and Oxburgh, 1967). At the same time, two new branches of solutions with slower plate velocities represent sluggish-lid convection cells where the strength of the plates determine the dynamics of the system.

Together with numerical simulations, the analytic model is used to explore and gain physical insight into several issues including: the thermal evolution of the Earth, why similar planets like Earth and Venus are so tectonically distinct, whether or not exoplanets will have plate tectonics, and how the asthenosphere affects plate-mantle coupling.