A method for improving the measurement of low-field magnetic susceptibility anisotropy in weak samples

Biedermann, Andrea R.; Lowrie, William; Hirt, Ann M.

doi:10.1016/j.jappgeo.2012.10.008

Cited by 21 publications

(32 citation statements)

References 13 publications

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“…The large P ‐values of the two forsterite crystals are due to their weak susceptibility [cf. Hrouda , ; Biedermann et al ., ]. Most samples display a prolate shape of the low‐field AMS ellipsoid (supporting information, Table B).…”

Section: Resultsmentioning

confidence: 99%

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Anisotropy of magnetic susceptibility in natural olivine single crystals

Biedermann

Pettke

Reusser

et al. 2014

Geochem Geophys Geosyst

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Mantle flow dynamics can cause preferential alignment of olivine crystals that results in anisotropy of physical properties. To interpret anisotropy in mantle rocks, it is necessary to understand the anisotropy of olivine single crystals. We determined anisotropy of magnetic susceptibility (AMS) for natural olivine crystals. High-field AMS allows for the isolation of the anisotropy due to olivine alone. The orientations of the principal susceptibility axes are related to the olivine's crystallographic structure as soon as it contains >3 wt % FeO. The maximum susceptibility is parallel to the c axis both at room temperature (RT) and at 77 K. The orientation of the minimum axis at RT depends on iron content; it is generally parallel to the a axis in crystals with 3-5 wt % FeO, and along b in samples with 6-10 wt % FeO. The AMS ellipsoid is prolate and the standard deviatoric susceptibility, k 0 , is on the order of 8*10 210 m 3 /kg for the samples with <1wt % FeO, and ranges from 3.1*10 29 m 3 /kg to 5.7*10 29 m 3 /kg for samples with 3-10 wt % FeO. At 77 K, the minimum susceptibility is along b, independent of iron content. The shape of the AMS ellipsoid is prolate for samples with <5 wt % FeO, but can be prolate or oblate for higher iron content. The degree of anisotropy increases at 77 K with p 0 77 5 7.1 6 0.5. The results from this study will allow AMS fabrics to be used as a proxy for olivine texture in ultramafic rocks with high olivine content.

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Section: Resultsmentioning

confidence: 99%

“…These samples display no relationship between the degree of anisotropy, expressed either as P or k′ , with iron content (supporting information, Figure B). The higher P ‐values of the forsterites can be attributed to the low value of mean susceptibility [ Biedermann et al ., ; Hrouda , ].…”

Section: Discussionmentioning

confidence: 99%

Anisotropy of magnetic susceptibility in natural olivine single crystals

Biedermann

Pettke

Reusser

et al. 2014

Geochem Geophys Geosyst

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“…[21] Because of the low susceptibility of the samples, careful cleaning and calibration of the sample holder were undertaken between each site, as even small amounts of ferromagnetic or paramagnetic dust may swamp the susceptibility signal of the samples [Borradaile et al, 2012]. In spite of the Kappabridge being sensitive to 0.5 × 10 À8 SI with an accuracy of 0.1%, the anisotropy values near zero can be anomalously high [Biedermann et al, 2013;Hrouda and Kapička, 1986;Rochette, 1987]. Although this is not thought to affect fabric orientations [Callot et al, 2010;Hrouda, 2004], its effect can cause problems when calculating the a N = Number of Samples; K m = Mean Susceptibility; K 1 , K 2 , K 3 = Orientations (Declination and Inclination) of the Principal Susceptibility Axes with 95% Confidence Ellipses; L = Lineation (L = K 1 /K 2 ); F = Foliation (F = k 2 /k 3 ); P j = Anisotropy Degree; T = Shape Parameter.…”

Section: Methodsmentioning

confidence: 99%

Magnetic fabrics in the basal ice of a surge-type glacier

Fleming

Lovell

Stevenson

et al. 2013

J. Geophys. Res. Earth Surf.

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[1] Anisotropy of magnetic susceptibility (AMS) has been shown to provide specific useful information regarding the kinematics of deformation within subglacially deformed sediments. Here we present results from debris-rich basal glacier ice to examine deformation associated with glacier motion. Basal ice samples were collected from Tunabreen, a polythermal surge-type glacier in Svalbard. The magnetic fabrics recorded show strong correlation with structures within the ice, such as sheath folds and macroscopic stretching lineations. Thermomagnetic, low-temperature susceptibility, varying field susceptibility, and isothermal remanent magnetism acquisition experiments reveal that the debris-rich basal ice samples have a susceptibility and anisotropy dominated by paramagnetic phases within the detrital sediment. Sediment grains entrained within the basal ice are inferred to have rotated into a preferential alignment during deformation associated with flow of the glacier. An up-glacier directed plunge of magnetic lineations and subtle deviation from bulk glacier flow at the margins highlight the importance of noncoaxial strain during surge propagation. The results suggest that AMS can be used as an ice petrofabric indicator for investigations of glacier deformation and interactions with the bed.

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“…In the Mauch Chunk red beds, where the effect of field‐induced anisotropy is small, only the shape parameter is affected, whereas the AMS degree and orientation of principal axes appear independent of the applied AF field. A synthetic study investigating the effect of noise on the reliability of AMS data [ Biedermann et al ., ] already demonstrated the higher sensitivity of the AMS shape than other parameters ( P , principal axes directions) to small changes in directional susceptibilities. For igneous samples from Bjerkreim Sokndal and part of the Fogo basalts, both U and P , but not the principal directions of the AMS ellipsoid, change due to field‐induced anisotropy.…”

Section: Discussionmentioning

confidence: 99%

Influence of static alternating field demagnetization on anisotropy of magnetic susceptibility: Experiments and implications

Biedermann

Jackson

Bilardello

et al. 2017

Geochem Geophys Geosyst

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Anisotropy of magnetic susceptibility (AMS) indicates the preferred orientation of a rock's constituent minerals. However, other factors can influence the AMS, e.g., domain wall pinning or domain alignment in ferromagnetic minerals. Therefore, it is controversial whether samples should be alternating field (AF) demagnetized prior to AMS characterization. This may remove the influence of natural remanent magnetization (NRM) or domain wall pinning on AMS; however, it may also result in field‐induced anisotropy. This study investigates the influence of stepwise AF and low‐temperature demagnetization on mean susceptibility, principal susceptibility directions, AMS degree and shape for sedimentary, metamorphic, and igneous rocks. Alternating fields up to 200 mT were applied along the sample x, y, and z axes, rotating the order for each step, to characterize the relationship between AMS principal directions and the last AF orientation. The changes in anisotropy, defined by the mean deviatoric susceptibility of the difference tensors, are between <2% and 270% of the AMS in NRM‐state. Variations in AMS parameters range from small changes in shape to complete reorientation of principal susceptibility axes, with the maximum susceptibility becoming parallel to the last AF direction. This is most prevalent in samples with low degrees of anisotropy in the NRM‐state. No clear correlations were found between field‐induced anisotropy and hysteresis properties. Therefore, we propose that future studies check any samples whose AMS is carried by ferromagnetic minerals and low anisotropy degrees for AF‐induced artifacts. These results highlight the need for understanding the AMS sources and carriers prior to any structural interpretation.

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A method for improving the measurement of low-field magnetic susceptibility anisotropy in weak samples

Cited by 21 publications

References 13 publications

Anisotropy of magnetic susceptibility in natural olivine single crystals

Anisotropy of magnetic susceptibility in natural olivine single crystals

Magnetic fabrics in the basal ice of a surge-type glacier

Influence of static alternating field demagnetization on anisotropy of magnetic susceptibility: Experiments and implications

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