A climate induced transition in the tectonic style of a terrestrial planet

We explore the possibility that an increase in the surface temperature of a terrestrial planet due to an enhanced concentration of atmospheric greenhouse gasses and/or increased solar luminosity could initiate a transition from an active-lid mode of mantle convection (e.g., plate tectonics) to an episodic or stagnant-lid mode (i.e., single plate planet). A scaling theory is developed to estimate the required temperature change as a function of the temperature dependence of mantle viscosity and the yield stress of the lithosphere. The theory relies on the assumptions that convective stresses scale with mantle viscosity and that a planet will adjust to surface temperature changes so as to maintain a surface heat flow that balances internal heat production. The theory is tested against a suite of numerical simulations of mantle convection. The comparisons are favorable. The combined theory and numerics suggest that if the yield stress for the earths' lithosphere is 30-35 MPa, then a surface temperature change of 60-120 degrees could shut down an active-lid mode of convection assuming present day conditions. Lower values are predicted for higher yield stresses and for earlier times in the earth geologic evolution. (C) 2008 Elsevier BY. All rights reserved.