Exploring Carbon Storage in the Deep Earth

Sarah Palaich, University of California, Los Angeles

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The study of the structure of carbon-bearing minerals at elevated pressures is important in many facets of science, including geology, condensed matter physics, and material science. Our research is motivated by the role of carbon in the deep earth. Carbon, in the form of CO2 or carbonate (CO32-) minerals, plays a fundamental role in the carbon cycle of Earth, both atmospherically and through subduction processes feeding the mantle. Studies of high-pressure, high-temperature phases of solid CO2 and carbonate minerals are important to understand the forms that carbon may adopt at the pressures and temperatures of Earth's interior. Knowledge of these forms gives insight into the composition of carbon reservoirs in the deep earth and the evolution of carbon in the earth through time. Two carbon studies will be showcased: 1. Recent experimental studies suggest that dolomite, a double carbonate, may be stable at the high pressures and temperatures of Earth’s deep mantle. Dolomite, ((CaM)(CO3)2, where M = Mg, Fe, Mn, Zn), undergoes a series of phase transformations with increasing pressures and temperatures. We have performed powder X-ray diffraction experiments on kutnohorite, Mn-rich dolomite, to 20 GPa and between 35 and 50 GPa. This preliminary study agrees with previous experimental work and expands the compositional range of dolomites stable at mantle conditions. 2. Neutron powder diffraction experiments on solid CO2 between 10 and 30 GPa and up to 700 K are presented from research done at Oak Ridge National Laboratory. These investigations aim to further elucidate the solid CO2 phase diagram and provide high pressure and temperature equation of state data for high-pressure CO2 polymorphs.

Abstract Author(s): Sarah Palaich, Abby Kavner, Craig Manning