For my thesis research, I am studying the formation of carbonate minerals in the Samail Ophiolite, Oman as a natural example of carbon dioxide (CO2) sequestration. An ophiolite is a segment of ocean crust and upper mantle tectonically exposed on land by obduction (overthrust), usually when an ocean basin closes. The goal of my thesis research is to determine the natural rate of carbonation of mantle rock (peridotite) at eight field locations in the Samail Ophiolite, which is one of the largest and best-exposed ophiolites in the world. To determine rates of carbonate formation, I am using a combination of field mapping to obtain carbonate volume estimates, radiogenic dating to determine carbonate formation ages, and cosmogenic dating to determine peridotite weathering rates. This enables me to quantify the residence time of carbon in three types of carbonate alteration products (veins, travertine deposits, and carbonate-rich cements) forming in the ophiolite.
Mantle peridotites are mainly composed of the minerals olivine and pyroxene, which are far from equilibrium with H2O and CO2 on Earth’s surface and are easily altered to hydrous silicates, Fe-oxides, and carbonates (calcite, magnesite, dolomite). These alteration reactions occur naturally at low temperatures when peridotite is exposed to water. My research is important because while natural carbonation of subaerial and submarine peridotite is commonly observed, the rate of this carbonation—and therefore the rate of CO2 uptake through this alteration mechanism—is poorly known. Determining the natural rate of peridotite carbonation is critical to assess the role of this potentially important “sink” in the global carbon cycle. The natural peridotite carbonation rate is also an essential, but poorly constrained, parameter in calculations evaluating the viability of using artificially-enhanced, in situ alteration of peridotite to mitigate the buildup of anthropogenic input to atmospheric CO2.