Unlocking information about fine magnetic particle assemblages from first-order reversal curve diagrams: Recent advances

Roberts, Andrew; Heslop, David; Zhao, Xiang; Oda, Hirokuni; Egli, Ramón; Harrison, R. J.; Hu, Pengxiang; Muxworthy, Adrian R.; Sato, Tetsuro

doi:10.1016/j.earscirev.2022.103950

Cited by 22 publications

(8 citation statements)

References 136 publications

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“…For samples containing multiple types of magnetic minerals, more reliable methods, such as FORC diagrams, are available for inferring domain states. In our investigations, remagnetised carbonates exhibit FORCs indicating a central ridge, attributed to non-interacting single domain/PSD grains (Roberts, 2022). This interpretation is supported by our direct microscopic observations (Figures 12,13).…”

Section: Tga-qmssupporting

confidence: 86%

“…Most of the Bambuí samples (Figure 7a') comprise an important contribution in the coercivity axis (Bc), with little contribution to the interaction axis (Bu), typical of non-interactive SD particles (Roberts et al, 2000;Roberts, 2022). Central-ridge contribution is also commonly related to the presence of biogenic magnetite, like magnetotactic bacterial magnetite in pelagic sediments (Roberts, 2011), whose sharpness is associated with little magnetostatic interactions.…”

Section: Forc Diagramsmentioning

confidence: 99%

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Clay minerals and continental-scale remagnetisation: a case study of South American Neoproterozoic carbonates

Bellon,

Trindade,

Williams

et al. 2023

Preprint

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Carbonate rocks frequently undergo remagnetisation events, which can partially/completely erase their primary detrital remanence and introduce a secondary component through thermoviscous and/or chemical processes. Despite belonging to different basins hundreds of kilometres apart, the Neoproterozoic carbonate rocks of South America (over the Amazon and São Francisco cratons) exhibit a statistically indistinguishable single-polarity characteristic direction carried by monoclinic pyrrhotite and magnetite, with paleomagnetic poles far from an expected detrital remanence. We use a combination of classical rock magnetic properties and micro-to-nanoscale imaging/chemical analysis using synchrotron radiation to examine thin sections of these remagnetised carbonate rocks. Magnetic data shows that most of our samples failed to present anomalous hysteresis properties, usually referred to as part of the “fingerprints” of carbonate remagnetisation. Combining scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), highly sensitive X-ray fluorescence (XRF), and X-ray absorption spectroscopy (XAS) revealed the presence of subhedral/anhedral magnetite, or spherical grains with a core-shell structure of magnetite surrounded by maghemite. These grains are within the pseudo-single domain size range (as well as most of the iron sulphides) and spatially associated with potassium-bearing aluminium silicates. Although fluid percolation and organic matter maturation might play an important role, smectite-illitisation seems a crucial factor controlling the growth of these phases. X-ray diffraction analysis identifies these silicates as predominantly highly crystalline illite, suggesting exposure to epizone temperatures. Therefore, we suggest that the remanence of these rocks should have been thermally reset during the final Gondwana assembly, and locked in a successive cooling event during the Early-Middle Ordovician.

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Section: Tga-qmssupporting

confidence: 86%

Section: Forc Diagramsmentioning

confidence: 99%

Clay minerals and continental-scale remagnetisation: a case study of South American Neoproterozoic carbonates

Bellon,

Trindade,

Williams

et al. 2023

Preprint

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“…For larger prolate and oblate particles with higher/lower ARs, NPN(P) structures form (Figures 3f and 4i). Such NPNP structures have been reported before for numerical models of FORC diagrams for vortex systems (e.g., Valdez‐Grijalva et al., 2018), however, they are usually associated with induced‐FORC (iFORC) diagrams, which are determined from transient and remanence FORC diagrams not modeled in this paper (Roberts et al., 2022; Tauxe et al., 2021; Zhao et al., 2017). These NPNP structures form when there are multiple metastable intermediate states during hysteresis, for example, nucleation/de‐nucleation of vortices, or flower structures or other metastable inhomogeneous magnetic domain states, switching between intermediate local energy minima (LEM; Carvallo et al., 2003; Valdez‐Grijalva et al., 2018, 2020).…”

Section: Discussionsupporting

confidence: 62%

Micromagnetic Determination of the FORC Response of Paleomagnetically Significant Magnetite Assemblages

Nagy,

Moreno,

Muxworthy

et al. 2024

Geochem Geophys Geosyst

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Micromagnetic modeling allows the systematic study of the effects of particle size and shape on the first‐order reversal curve (FORC) magnetic hysteresis response for magnetite particles in the single‐domain (SD) and pseudo‐single domain (PSD) particle size range. The interpretation of FORCs, though widely used, has been highly subjective. Here, we use micromagnetics to model randomly oriented distributions of particles to allow more physically meaningful interpretations. We show that one commonly found type of PSD particle—namely the single vortex (SV) particle—has far more complex signals than SD particles, with multiple peaks and troughs in the FORC distribution, where the peaks have higher switching fields for larger SV particles. Particles in the SD to SV transition zone have the lowest switching fields. Symmetrical and prolate particles display similar behavior, with distinctive peaks forming near the vertical axis of the FORC diagram. In contrast, highly oblate particles produce “butterfly” structures, suggesting that these are potentially diagnostic of particle morphology. We also consider FORC diagrams for distributions of particle sizes and shapes and produce an online application that users can use to build their own FORC distributions. There is good agreement between the model predictions for distributions of particle sizes and shapes, and the published experimental literature.

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“…We used FORC analysis to assess the grain size distribution of the magnetic minerals (e.g., Pike et al., 1999; Roberts et al., 2022). With their sensitivity to mineral grain size, FORC diagrams (Figure 4 and Figure S3 in Supporting Information ) show the coercivity characteristics of dominant mineral assemblages, exhibiting a dichotomy between the serpentinized and carbonated samples.…”

Section: Resultsmentioning

confidence: 99%

High‐Resolution Magnetic‐Geochemical Mapping of the Serpentinized and Carbonated Atlin Ophiolite, British Columbia: Toward Establishing Magnetometry as a Monitoring Tool for In Situ Mineral Carbonation

Tominaga

Beinlich

Lima

et al. 2023

Geochem Geophys Geosyst

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Magnetic remote sensing has been used in unlocking otherwise inaccessible information about geodynamic processes. Changes in magnetic anomalies, and magnetization distribution as inferred from magnetic data inversion, emerge from one or a combination of the contrast between geomagnetic polarity reversals at the time of remanence acquisition, source geometry/structural contrast (e.g., faults), and/or variations in magnetic carriers and rock composition. Inverse modeling of magnetic signals is applied to decipher crustal architecture, the nature

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Unlocking information about fine magnetic particle assemblages from first-order reversal curve diagrams: Recent advances

Cited by 22 publications

References 136 publications

Clay minerals and continental-scale remagnetisation: a case study of South American Neoproterozoic carbonates

Clay minerals and continental-scale remagnetisation: a case study of South American Neoproterozoic carbonates

Micromagnetic Determination of the FORC Response of Paleomagnetically Significant Magnetite Assemblages

High‐Resolution Magnetic‐Geochemical Mapping of the Serpentinized and Carbonated Atlin Ophiolite, British Columbia: Toward Establishing Magnetometry as a Monitoring Tool for In Situ Mineral Carbonation

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