Calibration of the calcite-water oxygen-isotope geothermometer at Devils Hole, Nevada, a natural laboratory
Geochimica et Cosmochimica Acta
By: T.B. Coplen
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Abstract
The ??18O of ground water (-13.54 ?? 0.05 ???) and inorganically precipitated Holocene vein calcite (+14.56 ?? 0.03 ???) from Devils Hole cave #2 in southcentral Nevada yield an oxygen isotopic fractionation factor between calcite and water at 33.7 ??C of 1.02849 ?? 0.00013 (1000 ln ??calcite-water = 28.09 ?? 0.13). Using the commonly accepted value of ???(??calcite-water)/???T of -0.00020 K-1, this corresponds to a 1000 ln ??calcite-water value at 25 ??C of 29.80, which differs substantially from the current accepted value of 28.3. Use of previously published oxygen isotopic fractionation factors would yield a calcite precipitation temperature in Devils Hole that is 8 ??C lower than the measured ground water temperature. Alternatively, previously published fractionation factors would yield a ??18O of water, from which the calcite precipitated, that is too negative by 1.5 ??? using a temperature of 33.7 ??C. Several lines of evidence indicate that the geochemical environment of Devils Hole has been remarkably constant for at least 10 ka. Accordingly, a re-evaluation of calcite-water oxygen isotopic fractionation factor may be in order. Assuming the Devils Hole oxygen isotopic value of ??calcite-water represents thermodynamic equilibrium, many marine carbonates are precipitated with a ??18O value that is too low, apparently due to a kinetic isotopic fractionation that preferentially enriches 16O in the solid carbonate over 18O, feigning oxygen isotopic equilibrium.
Suggested Citation
Coplen, T., 2007, Calibration of the calcite-water oxygen-isotope geothermometer at Devils Hole, Nevada, a natural laboratory: Geochimica et Cosmochimica Acta, v. 71, no. 16, p. 3948-3957, https://doi.org/10.1016/j.gca.2007.05.028.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Calibration of the calcite-water oxygen-isotope geothermometer at Devils Hole, Nevada, a natural laboratory |
| Series title | Geochimica et Cosmochimica Acta |
| DOI | 10.1016/j.gca.2007.05.028 |
| Volume | 71 |
| Issue | 16 |
| Year Published | 2007 |
| Language | English |
| Larger Work Type | Article |
| Larger Work Subtype | Journal Article |
| Larger Work Title | Geochimica et Cosmochimica Acta |
| First page | 3948 |
| Last page | 3957 |