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  Authigenic magnetite formation from goethite and hematite and chemical remanent magnetization acquisition

Till, J., Nowaczyk, N. (2018): Authigenic magnetite formation from goethite and hematite and chemical remanent magnetization acquisition. - Geophysical Journal International, 213, 3, 1818-1831.
https://doi.org/10.1093/gji/ggy083

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Till, Jessica1, Author              
Nowaczyk, N.2, Author              
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14.2 Geomechanics and Rheology, 4.0 Geomaterials, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum, ou_146035              
25.2 Climate Dynamics and Landscape Evolution, 5.0 Geoarchives, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum, ou_146046              

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Free keywords: Magnetic properties, Magnetic mineralogy and petrology, Remagnetization, Rock and mineral magnetism
 Abstract: The iron oxyhydroxide goethite is unstable at elevated temperatures and can transform to magnetite under reducing conditions. In this study, various heating experiments were conducted to simulate Fe-mineral transformations during pyrogenic or burial diagenesis alteration in the presence of organic matter. Thermomagnetic measurements, capsule heating experiments and thermochemical remanence acquisition measurements were performed to determine the effect of organic carbon additions on samples containing synthetic microcrystalline goethite, microcrystalline hematite or nanocrystalline goethite. Changes in magnetic properties with heating were monitored to characterize the magnetic behaviour of secondary magnetite and hematite formed during the experiments. Authigenic magnetite formed in all samples containing organic C, while goethite heated without organic C altered to poorly crystalline pseudomorphic hematite. The concentration of organic matter was found to have little influence on the rate or extent of reaction or on the characteristics of the secondary phases. Authigenic magnetite formed from microcrystalline goethite and hematite dominantly behaves as interacting single-domain particles, while nanophase goethite alters to a mixture of small single-domain and superparamagnetic magnetite. Authigenic magnetite and hematite both acquire a stable thermochemical remanence on heating to temperatures between 350 and 600 °C, although the remanence intensity acquired below 500 °C is much weaker than that at higher temperatures. Reductive transformation of fine-grained goethite or hematite is therefore a potential pathway for the production of authigenic magnetite and the generation of stable chemical remanence that may be responsible for remagnetization in organic-matter-bearing sedimentary rocks.

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 Dates: 2018
 Publication Status: Finally published
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 Identifiers: DOI: 10.1093/gji/ggy083
GFZPOF: p3 PT5 Georesources
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Title: Geophysical Journal International
Source Genre: Journal, SCI, Scopus, ab 2024 OA-Gold
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Pages: - Volume / Issue: 213 (3) Sequence Number: - Start / End Page: 1818 - 1831 Identifier: CoNE: https://gfzpublic.gfz-potsdam.de/cone/journals/resource/journals180