Determining timescales of natural carbonation of peridotite in the Samail Ophiolite, Sultanate of Oman

Abstract

Determining timescales of the formation and preservation of carbonate alteration products in mantle peridotite is important in order to better understand the role of this potentially important sink in the global carbon cycle and also to evaluate the feasibility of using artificially-enhanced, in situ formation of carbonates in peridotite to mitigate the buildup of anthropogenic CO2 emissions in the atmosphere. Timescales of natural carbonation of peridotite were investigated in the mantle layer of the Samail Ophiolite, Sultanate of Oman. Rates of ongoing, low-temperature CO2 uptake were estimated through 14C and 230Th dating of carbonate alteration products. Approximately 1-3 x 106 kg CO2/yr is sequestered in Ca-rich surface travertines and approximately 107 kg CO2/yr is sequestered in Mg-rich carbonate veins. Rates of CO2 removal were estimated through calculation of maximum erosion rates from cosmogenic 3He measurements in partiallyserpentinized peridotite bedrock associated with carbonate alteration products. Maximum erosion rates for serpentinized peridotite bedrock are ~5 to 180 m/Myr (average: ~40 m/Myr), which removes at most 105-106 kg CO2/yr through erosion of Mg-rich carbonate veins.