Coupled silicon-oxygen isotope fractionation traces Archaean silicification

K. Abraham, A. Hofmann, S. F. Foley, D. Cardinal, C. Harris, M. G. Barth, L. Andre

Research output: Contribution to journalArticlepeer-review

71 Citations (Scopus)


Silica alteration zones and cherts are a conspicuous feature of Archaean greenstone belts worldwide and provide evidence of extensive mobilisation of silica in the marine environment of the early Earth. In order to understand the process(es) of silicification we measured the silicon and oxygen isotope composition of sections of variably silicified basalts and overlying bedded cherts from the Theespruit, Hooggenoeg and Kromberg Formations of the Barberton Greenstone Belt, South Africa.The δ30Si and δ18O values of bulk rock increase with increasing amount of silicification from unsilicified basalts (-0.64%<δ30Si<-0.01% and +8.6%<δ18O<+11.9%) to silicified basalts (δ30Si and δ18O values as high as +0.81% and +15.6%, respectively). Cherts generally have positive isotope ratios (+0.215<δ30Si<+1.05% and +10.9<δ18O<+17.1), except two cherts, which have negative δ30Si values, but high δ18O (up to +19.5%).The pronounced positive correlations between δ30Si, δ18O and SiO2 imply that the isotope variation is driven by the silicification process which coevally introduced both 18O and 30Si into the basalts. The oxygen isotope variation in the basalts from about 8.6% to 15.6% is likely to represent temperature-dependent isotope fractionation during alteration. Our proposed model for the observed silicon isotope variation relies on a temperature-controlled basalt dissolution vs. silica deposition process.

Original languageEnglish
Pages (from-to)222-230
Number of pages9
JournalEarth and Planetary Science Letters
Issue number1-2
Publication statusPublished - 3 Jan 2011


  • Barberton Greenstone Belt
  • O isotopes
  • Si isotopes
  • Silicification
  • Two-step process

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Space and Planetary Science
  • Earth and Planetary Sciences (miscellaneous)


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