Fate of Subducted Carbonates: Structure Prediction and Solid Solution Modeling

GSTDTAP

项目编号	1551433
	Fate of Subducted Carbonates: Structure Prediction and Solid Solution Modeling
	Paul Asimow
主持机构	California Institute of Technology
项目开始年	2016
	2016-02-01
项目结束日期	2019-01-31
资助机构	US-NSF
项目类别	Continuing grant
项目经费	275358(USD)
国家	美国
语种	英语
英文摘要	Earth scientists agree that the regulation of carbon dioxide (CO2) concentrations in the atmosphere over geological timescales is an essential part of our planet's suitability for life. The essential ingredients of this long-term carbon cycle, which regulates the availability of carbon for the biosphere and the abundance of greenhouse gases in the atmosphere, are release of CO2 from volcanoes and return of CO2 return to the mantle along with old oceanic crust at subduction zones. In geochemistry, our ability to understand how a compound like CO2 will behave in such environments depends on identifying what mineral or fluid carries the carbon at each stage. Some information about this can be gained from natural observations and some from experiments, but there are key stages of the carbon cycle where calculation is the best tool at our disposal. This project will carry out a detailed computational study of the structure, thermodynamics, and stability of carbonate minerals under terrestrial mantle conditions, in order to constrain their role in storing and transporting carbon during subduction and melting processes. The approach combines tools from computational mineral physics, materials science, and classical thermodynamics to make predictions about complex solid solution phases at elevated pressure and finite temperature. Such a comprehensive approach is highly unusual in Earth science. Building on their success in predicting a new dense structure of CaMg(CO3)2 dolomite that is more stable than any observed experimentally, and in computing the phase diagram of end-member dolomite composition, the team has four goals for this project: (1) to determine the kinetics of transition among the pure dolomite phases; (2) to determine the influence of Fe2+ in the dolomite structure on phase stability, thermodynamic properties, and phase relations in Ca(Mg,Fe)(CO3)2 system; (3) to compute phase diagrams governing decarbonation in the CaO-MgO-FeO-SiO2-CO2 system; and (4) optimistically, to compute phase diagrams governing redox exchange between C and Fe in an extended system including reduced carbon and ferric iron. Their approach begins with prediction of stable crystal structures from first principles using a combination of evolutionary crystallography and density-functional theory. Thermodynamics of stable structures are characterized by a static equation of state and a fully anharmonic treatment of temperature effects and vibrational entropy via a highly efficient molecular dynamics approach. Solid solutions and configurational entropy are treated through detailed consideration of ordering phenomena and Boltzmann weighting of populated configurations. Finally, multicomponent phase diagrams are computed from the chemical potentials of components in relevant phases. This proposal will fund the stipend and computational resources required by a female graduate student being trained in an unusual combination of experimental and computational mineral physics approaches. Their workflow for computing the stability of novel carbonate phases relative to free CO2 has the possibility to connect to novel materials approaches to carbon sequestration.
来源学科分类	Geosciences - Earth Sciences
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/69109
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Paul Asimow.Fate of Subducted Carbonates: Structure Prediction and Solid Solution Modeling.2016.