Stable isotope disequilibria in travertine from high pH waters: Laboratory investigations and field observations from Oman

Details Stable isotope disequilibria in travertine from high pH waters: Laboratory investigations and field observations from Oman Stable isotope disequilibria in travertine from high pH waters: Laboratory investigations and field observations from Oman

May 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992gecoa..56.2041c&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 56, Issue 5, pp.2041-2050

Physics

3

Scientific paper

Ultramafic rocks in northern Oman host unusual, hyperalkaline groundwaters ( pH > 11.5) which precipitate inorganic travertine by diffusive uptake of atmospheric CO 2 after discharge. Stable isotope fractionation during CO 2 uptake results in strong depletions of the carbonate phase ( 13 C values as low as -27.5 and 18 O values of -16.9 PDB). Experiments under closed and open system conditions show that a kinetic depletion in the order of 15.5 for 13 C occurs during hydroxylation of aqueous CO 2 (CO 2(aq) + OH - reaction), attributed to a lower activation energy for 12 C-O vs 13 C-O. The observed 18 O depletion can be accounted for by CO 2 reaction with OH - ( 18 O OH - - H 2 O -40 ) without subsequent exchange and with no evidence of significant additional kinetic effects. Calculated reaction rates show hydroxylation to be the rate limiting step and that CO 2(g) -CO 2(aq) exchange at the gas/solution interface achieves isotopic equilibrium.

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