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Woods Hole Oceanographic Institution

Evelyn Mervine

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Sampling carbonate precipitate forming in an alkaline pool in peridotite. Samail Ophiolite, Oman, January 2009. (Ken Sims)


PhD Thesis Title: "Timescales of Natural Carbonation of Peridotite in the Samail Ophiolite, Sultanate of Oman." 

Collaborators:
Advisors: Susan Humphris (WHOI) and Ken Sims (U. Wyoming)
Other collaborators: Peter Kelemen (Lamont-Doherty, Columbia), Mark Kurz (WHOI), Juerg Matter (Lamont-Doherty, Columbia), Bill Jenkins (WHOI), Mark Roberts (WHOI)


For my PhD thesis research, I studied 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 was 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 used 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 enabled me to quantify the residence time of carbon in carbonate alteration products (veins and travertine deposits) 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.


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