Variations in planetary convection via the effect of climate on damage |
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| Authors: | W Landuyt D Bercovici |
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| Institution: | 1. Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada;2. Saskatchewan Isotope Laboratory, University of Saskatchewan, Saskatoon, Saskatchewan, Canada;1. National Aeronautics and Space Administration (NASA), Ames Research Center, Space Science Division, Moffett Field, CA 94035, United States;2. SETI Institute, 189 Bernardo Ave, Suite 100, Mountain View, CA 94043, United States;3. University of Virginia, Department of Environmental Sciences, P.O. Box 400123 Charlottesville, VA 22904-4123, United States;4. Massachusetts Institute of Technology, Department of Earth, Atmospheric and Planetary Sciences, Cambridge, Massachusetts 02139, United States;5. Lunar and Planetary Institute, 3600 Bay Area Blvd. Houston, TX 77058, United States;6. Southwest Research Institute, Boulder, CO 80302, United States;7. Earth and Planetary Science, University of California, Santa Cruz, CA 95064, United States;8. Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130, United States;9. Johns Hopkins University Applied Physics Laboratory, Laurel, MD, 20723, United States |
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| Abstract: | A new model for the generation of plate tectonics suggests an important interaction between a planet's climate and its lithospheric damage behavior; and thus provides a simple explanation for the tectonic difference between Earth and Venus. We propose that high surface temperatures will lead to higher healing rates (e.g. grain growth) in the lithosphere that will act to suppress localization, plate boundary formation, and subduction. This leads to episodic or stagnant lid convection on Venus because of its hotter climate. In contrast, Earth's cooler climate promotes damage and plate boundary formation. The damage rheology presented in this paper attempts to describe the evolution of grain size by allowing for grain reduction via deformational work input and grain growth via surface tension-driven coarsening. We explore the interaction of damage and healing in two-dimensional numerical convection simulations. We also develop a simple “drip-instability” model to test the hypothesis that the competition between damage and healing controls convective and plate tectonic style by modulating episodicity at subduction zones. At small values of damage, fA, (or large values of healing, kA) the lithosphere remains strong enough to resist subduction on time scales of billions of years. At intermediate values of fA and kA the lithosphere may become mobilized and allow for short bursts of tectonic behavior followed by periods of quiescence. At large (small) values of fA (kA ) the fineness is increased so that the viscosity of the plate boundary is reduced to allow for continuous, unimpeded subduction of lithosphere and plate-like deformation. The results suggest the feasibility of our proposed hypothesis that the interplay of climate and damage control the mode of tectonics on a planet. |
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