HR: 1340h
AN: U43C-1380    [Abstracts]
TI: Enhanced Natural Carbon Sequestration in Tectonically Exposed Mantle Peridotites
AU: * Matter, J M
EM: jmatter@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964-8000, United States
AU: Kelemen, P
EM: peterk@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964-8000, United States
AB: Carbon sequestration via mineral carbonation of calcium and magnesium silicates has been proposed but efficient carbonation is limited by the cost and energy requirement associated with mineral pretreatment (grinding, heating).
Weathering of tectonically exposed mantle peridotite (rich in olivine and minor pyroxene) forms solid carbonate minerals (magnesite, hydrated magnesite, and calcite) during interaction between ground water and either olivine and pyroxene, or their main hydration product, serpentine. Carbonates are deposited in veins and as interstitial minerals within weathered peridotites, and at the surface where alkaline, Ca-rich, CO₂-poor spring waters formed during serpentinization combine with atmospheric CO₂ to form large travertine deposits.
Literature data and our new analyses of alkaline spring waters emerging from peridotite section of the Samail Ophiolite in the Sultanate of Oman, suggest that 10 to 100 times more CO₂ is deposited in subsurface carbonate veins, compared to the volume of travertine formed on the surface. New radiocarbon ages show that both carbonate veins and travertine deposits in the large, tectonically exposed peridotite section of the Samail Ophiolite, formed on average in the past ~20,000 years. Using these data, we estimate that the approximate present day natural carbon sequestration rate is ~1E9 kg of CO₂ per year. This process is not particularly efficient, but the available mass of olivine, pyroxene and serpentine is large. Present day carbonation in Oman is restricted to the upper few 10's of meters, whereas the peridotite massif is several km thick in places. Thus, drilling and hydrofracturing, followed by forced circulation of meteoric or seawater, would likely enhance carbonation rates significantly. Carbonation rates may also be enhanced by exploiting the chemical potential energy inherent in exposing CO₂- and H₂O-poor mantle peridotite to the ocean and atmosphere. We present a simple 1D model that quantifies past suggestions that exothermic hydration of olivine and pyroxene to form serpentine can heat surrounding rocks. Heating, in turn, enhances hydration rates until temperature approaches the thermal stability limit of serpentine. Heating can be tuned to maintain near-constant temperature close to the optimal olivine carbonation rate, so that carbonation rates potentially increase 100 or 1000-fold compared to present day
DE: 3610 Geochemical modeling (1009, 8410)
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 3617 Alteration and weathering processes (1039)
DE: 4806 Carbon cycling (0428)
SC: Union [U]
MN: 2007 Fall Meeting