Isotopic geochemistry of sulphur
Abstract
The isotopic composition of sulphur has been determined for a large number of specimens representing the important geochemical phases in which sulphur is present. The most significant process that causes sulphur isotopic fractionation is the reduction of dissolved sulphate by bacteria, although other processes such as distillation of volcanic emanations, oxidation-reduction of H 2S, SO 2 and S during volcanism and sulphide-sulphate equilibrium under magmatie or hydrothermal conditions can be locally important. The new data are combined with earlier work in an attempt to define the range and average S 32/S 34 ratio of the various sulphur-bearing phases of the crust. The most important averages are meteorites 22.21, ocean sulphate 21.76, mafic rocks 22.16, plutonic silicic rocks 22.13, hydrothermal sulphides 22.13 and sedimentary sulphide 22.49 and post-Cambrian evaporite sulphate 21.80. A material balance calculation of the sulphur isotopes in the crust, although subject to considerable uncertainties, points to an average crustal composition of sulphur heavier than that for meteorites. No age effect is found for at least the last 2 × 10 9 years. Finally, a geochemical theory is described to account for the apparent distribution of sulphur isotopes in the lithosphere.
- Publication:
-
Geochimica et Cosmochimica Acta
- Pub Date:
- July 1959
- DOI:
- 10.1016/0016-7037(59)90112-7
- Bibcode:
- 1959GeCoA..16..201A