Two-Phase Damage and the Interactions between Earth's Mantle and Climate: From Plate Tectonic Feedbacks to Carbon Capture

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The interaction between the Earth's mantle and climate systems occurs through complex processes and over disparate time scales. On the geological time scale, the tectonic cycle buffers CO2 through mountain building and weathering, providing Earth with a temperate climate. The operation of plate tectonics, however, is not impervious to climatic conditions. Although liquid water is thought necessary to lubricate plate tectonics, recent theories postulate that a cool surface promotes lithospheric failure or damage, which then permits plate-like mantle flow on Earth, but not Venus. On human time scales, the rapid efflux of carbon from burning fossil fuels is possibly best mitigated by effectively returning CO2 to the mantle, i.e., by carbon sequestration in mafic and ultramafic rocks. Such processes of mantle-climate interaction, whether natural or man-made, involve multi-phase physics with the additional complexities of chemical reactions, grainsize evolution, and damage mechanics. This proposal is for the PI's on-going work on the development and application of two-phase damage theory; here we propose to address two issues:1. How plate tectonics initiated and plate-boundaries evolve remain unsolved questions in geodynamics, and provide tests of plate generation theories that go beyond modeling instantaneous present-day plate motions. Moreover, such plate-generation questions are possibly linked to climate evolution. If plate generation and a temperate Earth-like climate are mutually required of each other, then there is probably a critical surface temperature at which a planet does or does not achieve a cool/plate-like state, i.e., somewhere between Earth and Venus; this has implications for terrestrial planet evolution both within and outside our own solar system. The timing and vigor of plate initiation on early Earth would also have influenced Archaean climate, estimates of which are highly variable. The formation of new plate boundaries and plate evolution (shrinkage and reorganization) is also associated with climate variation (e.g., by changes in CO2 flux balance, the effect of continental configurations on ocean circulation, weathering, ice-formation, etc.). 2. How can damage enhanced percolation facilitate carbon sequestration in mantle derived rocks? In particular, how are fresh mineral surfaces for carbonate reactions generated by propagating damage fronts during injection of solutions of CO2 in mafic settings? For example, pulses of pressure or porosity waves in these settings would be associated with both void-generating and grainsize-reducing damage that would then enhance CO2 reactivity. These topics bracket the end-member time-scales in mantle-climate interactions. However, the natural long term processes can inform us how to mitigate short-term imbalances. Mitigating anthropogenic CO2 increases without pushing the problem to future generations requires a geologically long-term solution, and is best addressed by mimicking natural carbon buffering by weathering of mantle minerals. This proposal will combine long-term, planetary-scale perspectives with useful approaches to treating the Earth's mantle-climate system.This project is supported by the Geophysics Program and the Office of Cyberinfrastructure's CI-Reuse Venture Fund.