Two-Phase Grain Damage and Geochemical Interactions: From Early Tectonic Evolution to Climate and Energy Transitions

Yale University, New Haven CT

Investigators

Abstract

The interaction between Earth's interior and surface occurs through complex processes and over widely varying time scales. On the geological time scale, plate tectonics and mantle overturn govern the long-term evolution of the surface, atmosphere and ocean. Conversely, on the human time scale, the rapid efflux of CO2 from burning fossil fuels is possibly best mitigated by returning it as rapidly to the mantle, through carbon sequestration in mafic and ultramafic rocks. However, carbon-sequestration is only one of many climate-change mitigation strategies, and low-emission fuels like natural gas, which bridge the decades-long transition from traditional fossil fuels to renewable energies, are important as well. These complex issues can be treated commonly with a field of material physics called damage theory, i.e., to treat weakening and focusing of tectonic plate boundaries as well as microcracking in near-surface fluid-bearing rocks. This project continues development of one such theory called two-phase grain-damage theory. This theory simply states the energy going into damage is deformational work that is stored as surface energy on micro-crack surfaces and/or the boundaries between mineral grains. In particular, plate-generation and early plate tectonic and surface evolution will be studied using grain-damage theory, since grain-reduction during deformation (as in field observations of rocks called mylonites) is likely important for generating weak plate boundaries. This project will seek to answer how grain-damage combines with other effects such as mantle melting and petrological changes at plate boundaries, which are important for understanding how plate tectonics originated in the ancient Archean Earth. Secondly, two-phase "micro-crack" damage with chemical reactions will be used to address mineral carbon sequestration in mantle derived (mafic and ultramafic) rocks, along with development of transitional energy such as shale-gas. Questions we seek to answer are how carbonation reaction affects damage (e.g., stress crack-corrosion), and how chemical reactions, grain growth and permeability evolution influence seismicity during fluid injection? The project involves a fundamental theory that contributes to many problems of geological and environmental fluid mechanics, rock mechanics, material science (e.g., metallurgy), climate-change and energy. Although the topics of plate tectonic evolution and energy transitions cover disparate geological and human time-scales, they are approachable with similar scientific advancements. Moreover, the long-term evolution of the Earth can inform us how to mitigate short-term imbalances. For example, reducing anthropogenic CO2, without pushing the problem onto future generations, requires a geologically long-term solution, and is therefore best addressed by mimicking the Earth's natural surface evolution and cycles.