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.
