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Journal Article

Silicon and oxygen isotope fractionation in a silicified carbonate rock

Authors

Tatzel,  Michael
External Organizations;
GFZ SIMS Publications, Deutsches GeoForschungsZentrum;

Oelze,  Marcus
External Organizations;
GFZ SIMS Publications, Deutsches GeoForschungsZentrum;

Frick,  Daniel A.
External Organizations;
GFZ SIMS Publications, Deutsches GeoForschungsZentrum;

Di Rocco,  Tommaso
External Organizations;
GFZ SIMS Publications, Deutsches GeoForschungsZentrum;

Liesegang,  Moritz
External Organizations;
GFZ SIMS Publications, Deutsches GeoForschungsZentrum;

/persons/resource/stuff

Stuff,  Maria
3.6 Chemistry and Physics of Earth Materials, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;
GFZ SIMS Publications, Deutsches GeoForschungsZentrum;

/persons/resource/michawi

Wiedenbeck,  Michael
3.1 Inorganic and Isotope Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;
GFZ SIMS Publications, Deutsches GeoForschungsZentrum;

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Fulltext (public)

5025763.pdf
(Publisher version), 12MB

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Citation

Tatzel, M., Oelze, M., Frick, D. A., Di Rocco, T., Liesegang, M., Stuff, M., Wiedenbeck, M. (2024): Silicon and oxygen isotope fractionation in a silicified carbonate rock. - Chemical Geology, 658, 122120.
https://doi.org/10.1016/j.chemgeo.2024.122120


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5025763
Abstract
Silicon isotope fractionation during silicification is poorly understood and impedes our ability to decipher paleoenvironmental conditions from Si isotopes in ancient cherts. To investigate isotope fractionation during silica-for‑carbonate replacement we analyzed the microscale Si and O isotope composition in different silica phases in a silicified zebra dolostone as well as their bulk δ18O and Δ’17O compositions. The subsequent replacement of carbonate layers is mimicked by decreasing δ18O and δ30Si. The textural relationship and magnitude of Si and O isotope fractionation is best explained by near-quantitative silica precipitation in an open system with finite Si. A Rayleigh model for silicification suggests positive Ɛ30/28Si during silicification, conforming with predictions for isotope distribution at chemical equilibrium from ab-initio models. Application of the modelled Ɛ30Si-T relationship yields silicification temperatures of approx. 50 °C. To reconcile the δ18Ochert composition with these temperatures, the δ18O of the fluid must have been between −2.5 and − 4 ‰, compositions for which the quartz phases fall close to the oxygen equilibrium fractionation line in three-isotope space. Diagenetic silica replacement appears to occur in O and Si isotopic equilibrium allowing reconstructions of temperatures of silicification from Si isotopes and derive the δ18O composition of the fluid – a highly desired value needed for accurate reconstructions of the temperature- and δ18O histories of the oceans.