Magnetic Anisotropy in Single Crystals: A Review

Biedermann, Andrea R.

doi:10.3390/geosciences8080302

Cited by 38 publications

(36 citation statements)

References 116 publications

(242 reference statements)

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“…Also similar to MPF, exceptions to those empirical relationships have been observed; for example, different correlations exist between AMS orientation and flow direction in lava (Khan, ; Wing‐Fatt & Stacey, ), and certain minerals or grain sizes produce “inverse” or “anomalous” fabrics (Borradaile et al, ; Rochette, ; Rochette et al, ). Careful and systematic investigations of factors contributing to anisotropy (magnetocrystalline, shape and distribution anisotropy; Graham, ; Grégoire et al, ; Hargraves, ; Hargraves et al, ; Mainprice & Humbert, ; Stephenson, ) together with the characterization of single crystal properties (Biedermann, , and references therein) now allows one to model and understand even these anomalous and complex fabrics (Biedermann et al, ).…”

Section: Introductionmentioning

confidence: 99%

Magnetic Pore Fabrics: The Role of Shape and Distribution Anisotropy in Defining the Magnetic Anisotropy of Ferrofluid‐Impregnated Samples

Biedermann

2019

Geochem Geophys Geosyst

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Pore fabrics define physical properties of a rock, such as permeability and elasticity, both of which are important to many geological, hydrological, and environmental applications. Minerals and hence pores are often preferentially aligned, leading to anisotropy of physical properties and preferred flow directions. Preferred flow paths are defined by the shape and arrangement of pores, and a characterization of this pore fabric forms the basis for prediction of fluid flow directions. Magnetic pore fabrics (MPFs), that is, magnetic anisotropy measurements on ferrofluid-impregnated samples, are a promising and fast way to characterize the pore fabric of connected pores in 3-D, while analyzing a large number of pores with sizes down to 10 nm, without the need for any a priori knowledge about fabric orientation. Empirical relationships suggest that the MPF is related to the pore shape and orientation and approximates permeability anisotropy. This study uses models including shape and distribution anisotropy to better understand and quantify MPFs, using simple pore shapes and pore assemblies measured in previous studies. The results obtained in this study show that (1) shape anisotropy reliably predicts the MPF of single pores, (2) both shape and distribution anisotropy are needed to predict MPFs of pore assemblies, and (3) the anisotropy parameters P, L, and F are affected by the intrinsic susceptibility of the ferrofluid in addition to pore geometry. These findings can help explain some of the variability in empirical relationships and are an important step toward a quantitative understanding and application of MPFs in geological and environmental studies.Plain Language Summary To produce clean drinking water, use geothermal energy, or control contamination, it is necessary to understand how fluids flow underground. They have to find their way from pore to pore. As soon as pores are elongated or flattened, fluids can move more easily and thus faster in some directions than others. It is desirable to predict such preferred flow directions, and a good description of the pore space is needed to do so. Many methods exist to characterize the pore space, and one of these is based on the directional dependence of magnetic properties of samples, whose pores have been filled with strongly magnetic fluid. The method is efficient and promising, but unfortunately, it is not well understood how the magnetic data reflects the details of the pore space. The models developed here help define and quantify the factors controlling the observable magnetic properties. This understanding will make the method more applicable and useful in geothermal, hydrological, and environmental applications.

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Section: Introductionmentioning

confidence: 99%

Magnetic Pore Fabrics: The Role of Shape and Distribution Anisotropy in Defining the Magnetic Anisotropy of Ferrofluid‐Impregnated Samples

Biedermann

2019

Geochem Geophys Geosyst

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“…Consequently the microstructure of a deformed rock is often a complex combination of distinct microstructural features of diverse orientations and strengths. Therefore, it is not only important to evaluate the contributions of the main susceptibility carriers to the anisotropy 2 , it is also important to identify the processes responsible for AMS development and their eventual superposition 3–13 .…”

Section: Introductionmentioning

confidence: 99%

Localization effect on AMS fabric revealed by microstructural evidence across small-scale shear zone in marble

Kusbach

Machek

Roxerová

et al. 2019

Sci Rep

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Anisotropy of magnetic susceptibility (AMS) is regularly applied as a tool to infer structural analysis of deformation and flow in rocks, particularly, with low anisotropy. AMS integrates the magnetic signature of crystallographic and shape preferred orientation of all mineral grains present in the rock microstructure. Those preferred orientations result from multiple processes affecting the rock during its evolution, therefore the desirable AMS-strain relationship is not straightforward. Here we show that due to localization of deformation, AMS is indirectly dependent on the magnitude and character of deformation. In order to decipher the AMS-strain relationship, AMS studies should be accompanied by microstructural analyses combined with numerical modelling of magnetic fabric. A small-scale shear zone produced by single deformation event was studied. The resultant AMS fabric is “inverse” due to the presence of Fe-dolomite and controlled by calcite and dolomite crystallographic preferred orientations. The localized deformation resulted in the angular deviation between macroscopic and magnetic fabric in the shear zone, systematically increasing with increasing strain. This is a result of the presence of microstructural subfabrics of coarse porphyroclasts and fine-grained recrystallized matrix produced by localization.The localization of deformation is a multiscale and widespread process that should be considered whenever interpreting AMS in deformed rocks and regions.

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“…This inherent characteristic contributes to the low but measurable magnetic susceptibility along the paramagnetic trend. The magnetic susceptibility of individual minerals (e.g., Biedermann, ; Bleil & Petersen, ; Carmichael, ) displays more variability than does their density, but the susceptibility axis of the Henkel plot spans more than 6 orders of magnitude, so the FM endpoint susceptibility value could be higher or lower by a factor of 2 without significantly modifying the analysis or conclusions.…”

Section: Mineral Modellingmentioning

confidence: 99%

The Henkel Petrophysical Plot: Mineralogy and Lithology From Physical Properties

Enkin

Hamilton

Morris

2020

Geochem Geophys Geosyst

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The Henkel plot (logarithm of magnetic susceptibility versus density of rock samples) reveals that most rocks fall on either a "magnetite trend" or a "paramagnetic trend." Interpretation of gravity and magnetic surveys is improved when the mineralogical and lithological basis of these trends is understood. We present a quantitative mineralogical mixing model, involving the components QFC (quartz-feldspar-calcite), FM (ferromagnesian silicates), and M (magnetite) and discuss the geological processes which produce or modify these mixtures. Igneous rocks mostly plot on the magnetite trend, where the FM/M ratio is about 10. The density-susceptibility mineralogical mixing model is compatible with the CIPW mineral calculation for igneous classification from chemical analyses. Sedimentary and metamorphic processes usually involve oxidation, reduction, and/or iron loss, all which are magnetite-destructive and lead to petrophysical measurements along the paramagnetic trend where FM/M > 1,000. Mineralization, with the introduction of sulfides and oxides, leads to dense rocks which do not plot along the magnetite nor paramagnetic trends. This quantitative analysis provides a method to integrate geological processes in the interpretation of geophysical surveys. Plain Language SummaryThe Henkel plot (logarithm of magnetic susceptibility versus density of rock samples) is useful for linking geophysical data and geological interpretation. Our study merges thousands of rock physical properties measurements with their corresponding rock types and minerals. Given this globally applicable database, we calibrated a model reducing these many parameters to three basic groups of minerals and their physical properties. This model permits users of remote sensing data to come up with equivalent rock and mineral types and a spatial view of geological processes. It also allows geochemical data on igneous rocks to predict their physical behavior and control on regional geophysical mapping. Key Points: • The Henkel plot (logarithm of magnetic susceptibility versus density of rock samples) helps integrate geological and geophysical analysis • We present a quantitative mineralogical mixing model involving three components quartz-feldspar-calcite, ferromagnesian silicates, and magnetite • Major geological processes leading to petrophysical properties on different regions of the Henkel plot are easily explained

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Magnetic Anisotropy in Single Crystals: A Review

Cited by 38 publications

References 116 publications

Magnetic Pore Fabrics: The Role of Shape and Distribution Anisotropy in Defining the Magnetic Anisotropy of Ferrofluid‐Impregnated Samples

Magnetic Pore Fabrics: The Role of Shape and Distribution Anisotropy in Defining the Magnetic Anisotropy of Ferrofluid‐Impregnated Samples

Localization effect on AMS fabric revealed by microstructural evidence across small-scale shear zone in marble

The Henkel Petrophysical Plot: Mineralogy and Lithology From Physical Properties

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