Isotopic exchange in mineral-fluid systems. 4. The crystal chemical controls on oxygen isotope exchange rates in carbonate-H{sub 2}O and layer silicate-H{sub 2}O systems
Oxygen isotope exchange between minerals and water in systems far from chemical equilibrium is controlled largely by surface reactions such as dissolution-precipitation. In many cases, this behavior can be modeled adequately by a simple pseudo-first order rate model that accounts for changes in surface area of the solid. Previous modeling of high temperature isotope exchange data for carbonates, sulfates, and silicates indicated that within a given mineral group there appears to be a systematic relationship between rate and mineral chemistry. The author tested this idea by conducting oxygen isotope exchange experiments in the systems, carbonate-H{sub 2}O and layer silicate-H{sub 2}O at 300 and 350 C, respectively. Witherite (BaCO{sub 3}), strontianite (SrCO{sub 3}) and calcite (CaCO{sub 3}) were reacted with pure H{sub 2}O for different lengths of time (271--1,390 H) at 300 C and 100 bars. The layer silicates, chlorite, biotite and muscovite were reacted with H{sub 2}O for durations ranging from 132 to 3,282 h at 350 C and 250 bars. A detailed survey of grain sizes and grain habits using scanning electron microscopy (SEM) indicated that grain regrowth occurred in all experiments to varying extents. The isotopic rates (ln r) for the carbonate-H{sub 2}O system are {minus}20.75 {+-} 0.44, {minus}18.95 {+-} 0.62 and {minus}18.51 {+-} 0.48 mol O/m{sup 2} s for calcite, strontianite and witherite, respectively. The oxygen isotope exchange rates for layer silicate-H{sub 2}O systems are {minus}23.99 {+-} 0.89, {minus}23.14 {+-} 0.74 and {minus}22.40 {+-} 0.66 mol O/m{sup 2} s for muscovite, biotite and chlorite, respectively.
- Research Organization:
- Oak Ridge National Lab., TN (US)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-96OR22464
- OSTI ID:
- 20020874
- Journal Information:
- Geochimica et Cosmochimica Acta, Vol. 64, Issue 5; Other Information: PBD: Mar 2000; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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