Hysteresis of Natural Magnetite Ensembles: Micromagnetics of Silicate‐Hosted Magnetite Inclusions Based on Focused‐Ion‐Beam Nanotomography

Nikolaisen, Even; Harrison, R. J.; Fabian, Karl; McEnroe, Suzanne A.

doi:10.1029/2020gc009389

Cited by 28 publications

(58 citation statements)

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“…The second hypothesis implies that the magnetite and the accompanying phases precipitated from an Fe-bearing plagioclase, which became supersaturated with respect to magnetite (Wenk et al 2011;Biedermann et al 2016;Nikolaisen et al 2020). In this case, the magnetite and the accompanying phases were in contact with the crystal structure of the host plagioclase during their entire nucleation and growth history.…”

Section: Discussionmentioning

confidence: 99%

Formation pathways of oriented magnetite micro-inclusions in plagioclase from oceanic gabbro

Bian

Ageeva

Rečnik

et al. 2021

Contrib Mineral Petrol

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Plagioclase hosted needle- and lath-shaped magnetite micro-inclusions from oceanic gabbro dredged at the mid-Atlantic ridge at 13° 01–02′ N, 44° 52′ W were investigated to constrain their formation pathway. Their genesis is discussed in the light of petrography, mineral chemistry, and new data from transmission electron microscopy (TEM). The magnetite micro-inclusions show systematic crystallographic and shape orientation relationships with the plagioclase host. Direct TEM observation and selected area electron diffraction (SAED) confirm that the systematic orientation relations are due to the alignment of important oxygen layers between the magnetite micro-inclusions and the plagioclase host, a hypothesis made earlier based on electron backscatter diffraction data. Precipitation from Fe-bearing plagioclase, which became supersaturated with respect to magnetite due to interaction with a reducing fluid, is inferred to be the most likely formation pathway. This process probably occurred without the supply of Fe from an external source but required the out-diffusion of oxygen from the plagioclase to facilitate partial reduction of the ferric iron originally contained in the plagioclase. The magnetite micro-inclusions contain oriented lamellae of ilmenite, the abundance, shape and size of which indicate high-temperature exsolution from Ti-rich magnetite constraining the precipitation of the magnetite micro-inclusions to temperatures in excess of ~ 600 °C. This is above the Curie temperature of magnetite, and the magnetic signature of the magnetite-bearing plagioclase grains must, therefore, be considered as the thermoremanent magnetization.

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Section: Discussionmentioning

confidence: 99%

Formation pathways of oriented magnetite micro-inclusions in plagioclase from oceanic gabbro

Bian

Ageeva

Rečnik

et al. 2021

Contrib Mineral Petrol

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“…We here apply the general "slice-and-view" method for extracting data, processing the resulting image stack, and calculating micromagnetic models as it is described step-bystep in Nikolaisen et al [2020]. For this study only few modifications to the method were introduced to increase the quality and accuracy of the results.…”

Section: Methodsmentioning

confidence: 99%

“…Below only these changes are explained in sufficient detail to allow replication. All other details are described in Nikolaisen et al [2020].…”

Section: Methodsmentioning

confidence: 99%

“…These magnetite inclusions often occur as several micrometer long rods in multiple crystallographically defined directions. Given their common occurrence in nature, and their potential to carry reliable paleomagnetic information from ancient rocks [Bono et al, 2019], there is considerable interest in understanding the magnetic domain states of such inclusions [Nikolaisen et al, 2020] and the intrinsic magnetic anisotropy that arises from their non-random orientation distribution at the single-crystal scale. This anisotropy is of particular relevance when interpreting paleomagnetic measurements from single-crystal samples [Bono et al, 2019], as it has the potential to modify the relationship between the direction and intensity of paleomagnetic remanence and the ancient magnetizing field.…”

Section: Introductionmentioning

confidence: 99%

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Hysteresis parameters and magnetic anisotropy of silicate-hosted magnetite exsolutions

Nikolaisen

Harrison

Fabian

et al. 2022

Geophysical Journal International

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Summary Anisotropy of remanent magnetization and magnetic susceptibility are highly sensitive and important indicators of geological processes which are largely controlled by mineralogical parameters of the ferrimagnetic fraction in rocks. To provide new physical insight into the complex interaction between magnetization structure, shape, and crystallographic relations, we here analyse “slice-and-view” focused-ion-beam (FIB) nano-tomography data with micromagnetic modelling and single crystal hysteresis measurements. The data sets consist of 68 magnetite inclusions in orthopyroxene (Mg60) and 234 magnetite inclusions in plagioclase (An63) were obtained on mineral separates from the Rustenburg Layered Suite of the Bushveld Intrusive Complex, South Africa. Electron backscatter diffraction was used to determine the orientation of the magnetite inclusions relative to the crystallographic directions of their silicate hosts. Hysteresis loops were calculated using the finite-element micromagnetics code MERRILL for each particle in 20 equidistributed field directions and compared with corresponding hysteresis loops measured using a vibrating sample magnetometer (VSM) on silicate mineral separates from the same samples. In plagioclase the ratio of remanent magnetization to saturation magnetization (Mrs/Ms) for both model and measurement agree within $1.0\%$, whereas the coercivity (Hc) of the average modeled curve is 20 mT lower than the measured value of 60 mT indicating the presence of additional sources of high coercivity in the bulk sample. The VSM hysteresis measurements of the orthopyroxene were dominated by multi-domain (MD) magnetite, whereas the FIB location was chosen to avoid MD particles and thus contains only particles with diameters <500 nm that are considered to be the most important carriers of paleomagnetic remanence. To correct for this sampling bias, measured MD hysteresis loops from synthetic and natural magnetites were combined with the average hysteresis loop from the MERRILL models of the FIB region. The result shows that while the modeled small-particle fraction only explains $6\%$ of the best fit to the measured VSM hysteresis loop, it contributes $28\%$ of the remanent magnetization. The modelled direction of maximal Mrs/Ms in plagioclase is sub-parallel to [001]plag, whereas Hc does not show a strong orientation dependence. The easy axis of magnetic remanence is in the direction of the magnetite population normal to (150)plag and the maximum calculated susceptibility (χ*) is parallel to [010]plag. For orthopyroxene, the maximum Mrs/Ms, maximum χ* and the easy axis of remanence is strongly correlated to the elongation axes of magnetite in the [001]opx direction. The maximum Hc is oriented along [100]opx and parallel to the minimum χ*, which reflects larger vortex nucleation fields when the applied field direction approaches the short axis. The maximum Hc is therefore orthogonal to the maximum Mrs/Ms, 16 controlled by axis-aligned metastable single-domain states at zero field. The results emphasize that the nature of anisotropy in natural magnetite does not just depend on the particle orientations, but on the presence of different stable and metastable domain states, and the mechanism of magnetic switching between them. Magnetic modelling of natural magnetic particles is therefore a vital method to extract and process anisotropic hysteresis parameters directly from the primary remanence carriers.

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“…netite and titanomagnetite) within silicates are widely distributed in marine sediments, and their size ranges from a few nanometers to several micrometers with variable morphologies (Chang, Bolton, et al, 2016;Hong et al, 2019;Hounslow, 1996;Hounslow & Morton, 2004;Nikolaisen et al, 2020;Usui et al, 2018;Zhang et al, 2018). It is suggested that they have stable single domain (SD)like magnetic properties and can be preserved in perturbed environments due to the protection of silicate (Chang, Bolton, et al, 2016;Chang et al, 2021), thus recording a reliable paleomagnetic and paleoenvironmental information.…”

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confidence: 99%

Quantifying Contributions of Magnetic Inclusions Within Silicates to Marine Sediments: A Dissolution Approach to Isolating Volcanic Signals for Improved Paleoenvironmental Reconstruction

Jiang

Zhao

et al. 2021

JGR Solid Earth

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Hysteresis of Natural Magnetite Ensembles: Micromagnetics of Silicate‐Hosted Magnetite Inclusions Based on Focused‐Ion‐Beam Nanotomography

Cited by 28 publications

References 60 publications

Formation pathways of oriented magnetite micro-inclusions in plagioclase from oceanic gabbro

Formation pathways of oriented magnetite micro-inclusions in plagioclase from oceanic gabbro

Hysteresis parameters and magnetic anisotropy of silicate-hosted magnetite exsolutions

Quantifying Contributions of Magnetic Inclusions Within Silicates to Marine Sediments: A Dissolution Approach to Isolating Volcanic Signals for Improved Paleoenvironmental Reconstruction

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