Carbonation rates of peridotite in the Samail Ophiolite, Sultanate of Oman, constrained through ~(14)C dating and stable isotopes

摘要

Detailed ~(14)C dating as well as stable C and O isotope analyses were conducted on carbonates formed during alteration of the peridotite layer of the Samail Ophiolite, Sultanate of Oman. ~(14)C results obtained in this and previous studies indicate that surface travertines range in age from modern to >45,000 yr BP, indicating long-term deposition and preservation. Travertine deposition rates in two localities were ~0.1 to 0.3 mm/yr between ~30,000 and 45,000 yr BP. Using an estimate of total travertine area, this would result in a maximum of ~1000 to 3000 m3/yr of travertine being deposited throughout the ophiolite during this time period. This travertine deposition would have sequestered a maximum of ~1 to 3 × 10~6 kg CO_2/yr. Ca-rich carbonate veins that are associated with the surface travertine deposits have ages ranging from ~4000 to 36,000 yr BP (average: 15,000 yr BP). Mg-rich carbonate veins exposed in outcrops have ages ranging from ~8000 to 45,000 yr BP (average: 35,000 yr BP). Detailed sampling from numerous locations (3 locations in this study and 10 locations in the previous studies) indicates that no carbonate veins from the natural peridotite weathering surface are older than the ~50,000 yr BP dating limit of ~(14)C. However, ~(14)C dating of Mg-rich carbonate veins from three roadcut exposures (Qafeefah, Fanja, and Al-Wuqbah) indicates that a significant number of roadcut veins are ~(14)C dead (>50,000 yr BP). A location weighted average indicates that ~40% of veins sampled at the three roadcuts are ~(14)C dead. An average including veins sampled at both roadcuts and outcrops indicates that overall ~8% of Mg-rich carbonate veins are ~(14)C dead. Mg-rich carbonate veins are estimated to sequester on the order of 107 kg CO_2/yr throughout the ophiolite.