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Intracrystalline site preference of oxygen isotopes in goethite: A single-mineral paleothermometer

Miller, Hayden B. D. and Farley, Kenneth A. and Vasconcelos, Paulo M. and Mostert, Albert and Eiler, John M. (2020) Intracrystalline site preference of oxygen isotopes in goethite: A single-mineral paleothermometer. Earth and Planetary Science Letters, 539 . Art. No. 116237. ISSN 0012-821X. https://resolver.caltech.edu/CaltechAUTHORS:20200330-070628054

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Abstract

The crystal structure of goethite, FeO(OH), has two distinct oxygen sites, one with exclusively Fe-O bonds, the other with bonds to both iron and hydrogen. We developed a method to assess the oxygen isotope contrast between these sites by measuring both the bulk goethite and the oxygen released in the conversion of goethite to hematite. The method involves collecting the water released by dehydroxylation, fluorinating that population of extracted atoms, and measuring the resulting oxygen isotope composition (extracted δO¹⁸). Then, on a separate aliquot, all structural oxygen is fluorinated and measured (bulk δO¹⁸). Using synthetic goethite precipitates grown under controlled environmental conditions, we found significant temperature-dependent fractionation, ε_(bulk-extracted)=(5.51±0.26)×(10⁶/T²)−(44.5±2.8); T in Kelvin). This intracrystalline fractionation forms the basis of a single-phase paleothermometer with an estimated uncertainty of ∼2-3°C. The temperature dependence appears to be independent of the isotopic composition of the parent fluid from which the goethite formed and the pH of that fluid. This intracrystalline thermometer can be used to simultaneously determine the formation temperature of a goethite and the isotopic composition of the water from which it formed. Natural goethites analyzed with this technique yield geologically reasonable formation temperatures of between 15 and 41°C.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.epsl.2020.116237DOIArticle
ORCID:
AuthorORCID
Miller, Hayden B. D.0000-0001-7305-928X
Farley, Kenneth A.0000-0002-7846-7546
Additional Information:© 2020 Elsevier B.V. Received 29 June 2019, Revised 21 January 2020, Accepted 16 March 2020, Available online 27 March 2020. This work was supported by a gift from the Chair's Council of the Caltech Division of Geological and Planetary Sciences. Synthetic goethite precipitation and synchrotron XRD experiments were funded by Australian Research Council LP0455770, Australian Synchrotron Grant FI3897, and an Australian Postgraduate Award to Albert Mostert. We also thank James Hagadorn and the Denver Museum of Nature and Science for providing the two Pikes Peak samples (DMNH-14510 and DMNH-10029). We gratefully acknowledge comments by Crayton Yapp and two anonymous reviewers.
Funders:
Funding AgencyGrant Number
Caltech Division of Geological and Planetary SciencesUNSPECIFIED
Australian Research CouncilLP0455770
Australian SynchrotronFI3897
Subject Keywords:paleoclimate; oxygen isotopes; goethite; iron oxide; geochronology; weathering
Record Number:CaltechAUTHORS:20200330-070628054
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200330-070628054
Official Citation:Hayden B.D. Miller, Kenneth A. Farley, Paulo M. Vasconcelos, Albert Mostert, John M. Eiler, Intracrystalline site preference of oxygen isotopes in goethite: A single-mineral paleothermometer, Earth and Planetary Science Letters, Volume 539, 2020, 116237, ISSN 0012-821X, https://doi.org/10.1016/j.epsl.2020.116237. (http://www.sciencedirect.com/science/article/pii/S0012821X20301801)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:102159
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:30 Mar 2020 15:03
Last Modified:30 Mar 2020 15:03

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