Computer Science
Scientific paper
Oct 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983gecoa..47.1681c&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 47, Issue 10, pp.1681-1693
Computer Science
14
Scientific paper
Oxygen isotopic exchange between minerals and fluids proceeds through two mechanisms: 1. (1) surface reactions (dissolution, precipitation) and 2. (2) diffusion of oxygen-bearing species along lattice planes or crystal imperfections. The rate constants for the first type of mechanism are related as follows: where W and S are the number of moles of oxygen in the fluid and solid, respectively, A is the surface area, t is time and F is the fraction of oxygen isotopic exchange. Examination of the published experimental data on oxygen isotopic exchange reactions between various phases ( e.g. , silicates, carbonates, sulfates) and aqueous fluids using the above equation yields rate constants of between 10 -4 and 10 -8 moles m -2 sec -1 in the temperature range of 800 to 250°C, and activation energies of between 8 and 22 Kcal mol -1 . These activation energies are similar to those of chemical reactions involving fluids and mineral surfaces. Rates of oxygen isotopic exchange accompanying diffusion of oxygen-bearing compounds through mineral lattices are also calculated from published experimental data using equations that take into account fluid/mineral mass ratios of the systems. These rates are found to be several orders of magnitude less than those accompanying surface reactions when the temperature, fluid/mineral mass ratio and the grain radius of the mineral are similar. These data suggest that the oxygen isotopic exchange reactions between fluids and rocks in natural systems may proceed in two steps: the first through a surface-controlled mechanism when the fluids and minerals are out of chemical equilibrium, and then through a diffusional mechanism once the systems attain chemical equilibrium.
Cole David R.
Lasaga Antonio C.
Ohmoto Hiroshi
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