Calcite carbon isotope fractionation

Romanek CS, Grossman EL, Morse JW (1992) Carbon isotopic fractionation in synthetic aragonite and calcite Effects of temperature and precipitation rate. Geochim Cosmochim Acta 56 419-430 Rowe MW, Clayton RN, Mayeda TK (1994) Oxygen isotopes in separated components of Cl and CM meteorites. Geochim Cosmochim Acta 58 5341-5347... 

Chacko T, Mayeda T. K., Clayton R. N., and Goldsmith J. R. (1991). Oxygen and carbon isotope fractionations between CO2 and calcite. Geochim. Cosmochim. Acta, 55 2867-2882. 

Romanek C. S., Grossman E. L. and Morse J. W. (1989). Carbon isotope fractionation in aragonite and calcite Experimental study of temperature and kinetic effects. Geol Soc. Amer. Abstr. Prog., 2LA76. 

Carbon isotope fractionations under equilibrium conditions are important not only at low-temperature, but also at high temperatures within the system carbonate, CO2, graphite, and CH4. Of these, the calcite-graphite fractionation has become a useful geothermometer (e.g.. Valley and O Neil 1981 Scheele and Hoefs 1992 Kitchen and Valley 1995) (see discussion on p. 227). 

Scheele N, Hoefs J (1992) Carbon isotope fractionation between calcite, graphite and CO2. Contr Miner Petrol 112 35 5... 

A key question is then the relationship between the isotopic composition of the C02(g) in the soil and the CO2 dissolved in the mineral species growing in the soils. The equilibrium carbon isotope fractionations between C02(g) and carbonate minerals (CaC03 (both calcite and aragonite polymorphs), MgC03 (magnesite)) are known experimentally and can be accurately calculated from quantum chemistry (75). Overall, carbon in carbonate minerals is isotopically heavier than carbon in C02(g) by about... 

Romanek, C. S., E. L. Grossman and J. W. Morse (1992) Carbon isotope fractionation in S5mthetic aragonite and calcite effects of temperature and precipitation rate. Geochim. Cosmochim. Acta 56,419-30. 

We are not aware of any direct calculations of partition function ratios for supercritical fluids. However, experimentally determined oxygen and carbon isotope fractionations in the C02-calcite system at supercritical conditions are in good agreement with fractionations derived from theoretical calculations (Chacko et al. 1991 Scheele and Hoefs 1992 Rosenbaum 1994). This suggests that supercritical CO2 is well represented by the ideal gas approximation as the calculations were made on this basis (Rosenbaum... 

Figure 4. Temperature-dependence of oxygen or carbon isotope fractionation factors in some representative mineral-fluid and mineral-mineral systems as indicated by theoretical calculations. All curves are for oxygen isotope fractionations except for C02-calcite, which is for carbon isotope fractionations.

Bottinga, Y. 1969 Calculated fractionation factors for carbon and hydrogen isotope exchange in the system calcite-carbon dioxide-graphite-methane-hydrogen-water vapour. Geochimica et CosmochimicaActa 33 49-64. 

For crystals with molecule-like constituents, like the BO, " and BO4 " groups in some borates, semi-quantitative models of the molecular component as a gas-phase entity have been proposed (Oi et al. 1989). This is conceptually similar to the approximation made for species in solution, although in practice most studies of crystals consider additional frequencies that reflect inter-molecular vibrations. The spectroscopic data on these vibrations (which typically have lower frequencies than the intra-molecular vibrations) are often available, at least approximately, from infrared and Raman spectroscopy and elastic properties. This type of hybrid molecule-in-crystal model has been applied to many minerals in theoretical studies of carbon and oxygen isotope fractionation, the most noteworthy being studies of calcite (Bottinga 1968 Chacko et al. 1991) and sihcates (Kieffer 1982). Because specfroscopic dafa are always incomplete (especially for subsfances substifufed wifh rare isolopes), some amounl of vibralional modeling is necessary. 

Bottinga Y (1968) Calculations of fractionation factors for carbon and oxygen isotope exchange in the system calcite-carbon dioxide-water. J Phys Chem 72 800-808 Bullen TD, White AF, Childs CW, Vivit DV, Schulz MS (2001) Demonstration of significant abiotic iron isotope fractionation in nature. Geology 29 699-702... 

Rosenbaum J. M. (1994). Stable isotope fractionation between carbon dioxide and calcite at 900°C. Geochim. Cosmochim. Acta, 58 3747-3753. 

Gruber N, et al. (1999) Spatiotemporal patterns of carbon-13 in the global surface oceans and the oceanic Suess effect. Global Biogeochem Cycles 13 307-335 Gussone N, et al. (2005) Calcium isotope fractionation in calcite and aragonite. Geochim Cosmochim Acta 69 4485 494... 

One of the most important uses of oxygen isotopes in carbonates is as geothermometers. Isotope fractionation is pressure independent (Clayton et al., 1975), giving it an advantage over other geothermometers which are generally both temperature and pressure dependent. The equation for calculating the temperature at which calcite precipitates from water is ... 

---