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RESEARCH PRODUCT
Coupled silicon-oxygen isotope fractionation traces Archaean silicification
Chris HarrisMatthias BarthLuc AndréKathrin AbrahamAxel HofmannStephen F. FoleyDamien Cardinalsubject
Basalt010504 meteorology & atmospheric sciencesIsotopeδ18O[SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph]ArcheanGeochemistry[PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph]Greenstone belt010502 geochemistry & geophysicsEarly Earth01 natural sciencesIsotopes of oxygenGeophysicsIsotope fractionation13. Climate actionSpace and Planetary ScienceGeochemistry and PetrologyEarth and Planetary Sciences (miscellaneous)14. Life underwaterGeology0105 earth and related environmental sciencesdescription
International audience; 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‰ 30Si 18O 30Si and δ18O values as high as + 0.81‰ and + 15.6‰, respectively). Cherts generally have positive isotope ratios (+ 0.21‰ 30Si 18O 30Si 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.
year | journal | country | edition | language |
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2011-01-01 |