Low-temperature magnetic anisotropy in micas and chlorite

Andrea R. Biedermann; Christian Bender Koch; Wolfram E A Lorenz; Ann M. Hirt

doi:10.1016/j.tecto.2014.01.015

Low-temperature magnetic anisotropy in micas and chlorite

Andrea R. Biedermann, Christian Bender Koch, Wolfram E A Lorenz, Ann M. Hirt^*

^*Corresponding author for this work

Department of Chemistry

26 Citations (Scopus)

Abstract

Phyllosilicates, such as micas and chlorite, are common rock-forming minerals and often show preferred orientation in deformed rocks. In combination with single-crystal anisotropy, this leads to anisotropy of physical properties in the rock, such as magnetic susceptibility. In order to effectively use the magnetic anisotropy to understand a rock fabric, it is necessary to identify the minerals responsible for the magnetic anisotropy. Techniques have been developed to separate contributions of the ferrimagnetic, antiferromagnetic, paramagnetic, and diamagnetic susceptibilities to the anisotropy of magnetic susceptibility. Because diamagnetic and paramagnetic susceptibility are both linearly dependent on field, separation of the anisotropic contributions requires understanding how the degree of anisotropy of the paramagnetic susceptibility changes as a function of temperature. Note that diamagnetic susceptibility is not dependent on temperature. The increase in paramagnetic anisotropy at low temperature is used to separate the paramagnetic and diamagnetic subfabrics, and can be expressed by the p₇₇ factor. In this study, we determined p₇₇, which is the change in the degree of anisotropy (δk) between room temperature (298 K) and liquid nitrogen temperature (77 K), for a series of micas and chlorite. The paramagnetic susceptibility ellipsoid is highly oblate with the minimum principal susceptibility normal to the silicate layers at both 77 K and RT. The degree of anisotropy δk increases by a factor of approximately 6.3-8.7 for individual samples of muscovite, phlogopite and chlorite on cooling from RT to 77 K and between 11.2 and 12.4 for biotite. A decrease in temperature enhances the paramagnetic anisotropy in a mineral. Biotite exhibits a relatively stronger enhancement due to the onset of magnetic ordering below ~ 100 K. This can have important implications for interpreting low temperature anisotropy in mudstones, mica schists and gneisses.

Original language	English
Journal	Tectonophysics
Volume	629
Pages (from-to)	63-74
Number of pages	12
ISSN	0040-1951
DOIs	https://doi.org/10.1016/j.tecto.2014.01.015
Publication status	Published - 2014

Keywords

AMS (anisotropy of magnetic susceptibility)
Biotite
Chlorite
Muscovite
Phlogopite
Phyllosilicate

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10.1016/j.tecto.2014.01.015

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@article{1846cc3950e8469ba40b7fc423f6fe30,

title = "Low-temperature magnetic anisotropy in micas and chlorite",

abstract = "Phyllosilicates, such as micas and chlorite, are common rock-forming minerals and often show preferred orientation in deformed rocks. In combination with single-crystal anisotropy, this leads to anisotropy of physical properties in the rock, such as magnetic susceptibility. In order to effectively use the magnetic anisotropy to understand a rock fabric, it is necessary to identify the minerals responsible for the magnetic anisotropy. Techniques have been developed to separate contributions of the ferrimagnetic, antiferromagnetic, paramagnetic, and diamagnetic susceptibilities to the anisotropy of magnetic susceptibility. Because diamagnetic and paramagnetic susceptibility are both linearly dependent on field, separation of the anisotropic contributions requires understanding how the degree of anisotropy of the paramagnetic susceptibility changes as a function of temperature. Note that diamagnetic susceptibility is not dependent on temperature. The increase in paramagnetic anisotropy at low temperature is used to separate the paramagnetic and diamagnetic subfabrics, and can be expressed by the p 77 factor. In this study, we determined p 77, which is the change in the degree of anisotropy (δk) between room temperature (298 K) and liquid nitrogen temperature (77 K), for a series of micas and chlorite. The paramagnetic susceptibility ellipsoid is highly oblate with the minimum principal susceptibility normal to the silicate layers at both 77 K and RT. The degree of anisotropy δk increases by a factor of approximately 6.3-8.7 for individual samples of muscovite, phlogopite and chlorite on cooling from RT to 77 K and between 11.2 and 12.4 for biotite. A decrease in temperature enhances the paramagnetic anisotropy in a mineral. Biotite exhibits a relatively stronger enhancement due to the onset of magnetic ordering below ~ 100 K. This can have important implications for interpreting low temperature anisotropy in mudstones, mica schists and gneisses.",

keywords = "AMS (anisotropy of magnetic susceptibility), Biotite, Chlorite, Muscovite, Phlogopite, Phyllosilicate",

author = "Biedermann, {Andrea R.} and {Bender Koch}, Christian and Lorenz, {Wolfram E A} and Hirt, {Ann M.}",

note = "Methods and applications of magnetic anisotropy: A tribute to Graham Borradaile",

year = "2014",

doi = "10.1016/j.tecto.2014.01.015",

language = "English",

volume = "629",

pages = "63--74",

journal = "Tectonophysics",

issn = "0040-1951",

publisher = "Elsevier",

}

TY - JOUR

T1 - Low-temperature magnetic anisotropy in micas and chlorite

AU - Biedermann, Andrea R.

AU - Bender Koch, Christian

AU - Lorenz, Wolfram E A

AU - Hirt, Ann M.

N1 - Methods and applications of magnetic anisotropy: A tribute to Graham Borradaile

PY - 2014

Y1 - 2014

N2 - Phyllosilicates, such as micas and chlorite, are common rock-forming minerals and often show preferred orientation in deformed rocks. In combination with single-crystal anisotropy, this leads to anisotropy of physical properties in the rock, such as magnetic susceptibility. In order to effectively use the magnetic anisotropy to understand a rock fabric, it is necessary to identify the minerals responsible for the magnetic anisotropy. Techniques have been developed to separate contributions of the ferrimagnetic, antiferromagnetic, paramagnetic, and diamagnetic susceptibilities to the anisotropy of magnetic susceptibility. Because diamagnetic and paramagnetic susceptibility are both linearly dependent on field, separation of the anisotropic contributions requires understanding how the degree of anisotropy of the paramagnetic susceptibility changes as a function of temperature. Note that diamagnetic susceptibility is not dependent on temperature. The increase in paramagnetic anisotropy at low temperature is used to separate the paramagnetic and diamagnetic subfabrics, and can be expressed by the p 77 factor. In this study, we determined p 77, which is the change in the degree of anisotropy (δk) between room temperature (298 K) and liquid nitrogen temperature (77 K), for a series of micas and chlorite. The paramagnetic susceptibility ellipsoid is highly oblate with the minimum principal susceptibility normal to the silicate layers at both 77 K and RT. The degree of anisotropy δk increases by a factor of approximately 6.3-8.7 for individual samples of muscovite, phlogopite and chlorite on cooling from RT to 77 K and between 11.2 and 12.4 for biotite. A decrease in temperature enhances the paramagnetic anisotropy in a mineral. Biotite exhibits a relatively stronger enhancement due to the onset of magnetic ordering below ~ 100 K. This can have important implications for interpreting low temperature anisotropy in mudstones, mica schists and gneisses.

AB - Phyllosilicates, such as micas and chlorite, are common rock-forming minerals and often show preferred orientation in deformed rocks. In combination with single-crystal anisotropy, this leads to anisotropy of physical properties in the rock, such as magnetic susceptibility. In order to effectively use the magnetic anisotropy to understand a rock fabric, it is necessary to identify the minerals responsible for the magnetic anisotropy. Techniques have been developed to separate contributions of the ferrimagnetic, antiferromagnetic, paramagnetic, and diamagnetic susceptibilities to the anisotropy of magnetic susceptibility. Because diamagnetic and paramagnetic susceptibility are both linearly dependent on field, separation of the anisotropic contributions requires understanding how the degree of anisotropy of the paramagnetic susceptibility changes as a function of temperature. Note that diamagnetic susceptibility is not dependent on temperature. The increase in paramagnetic anisotropy at low temperature is used to separate the paramagnetic and diamagnetic subfabrics, and can be expressed by the p 77 factor. In this study, we determined p 77, which is the change in the degree of anisotropy (δk) between room temperature (298 K) and liquid nitrogen temperature (77 K), for a series of micas and chlorite. The paramagnetic susceptibility ellipsoid is highly oblate with the minimum principal susceptibility normal to the silicate layers at both 77 K and RT. The degree of anisotropy δk increases by a factor of approximately 6.3-8.7 for individual samples of muscovite, phlogopite and chlorite on cooling from RT to 77 K and between 11.2 and 12.4 for biotite. A decrease in temperature enhances the paramagnetic anisotropy in a mineral. Biotite exhibits a relatively stronger enhancement due to the onset of magnetic ordering below ~ 100 K. This can have important implications for interpreting low temperature anisotropy in mudstones, mica schists and gneisses.

KW - AMS (anisotropy of magnetic susceptibility)

KW - Biotite

KW - Chlorite

KW - Muscovite

KW - Phlogopite

KW - Phyllosilicate

U2 - 10.1016/j.tecto.2014.01.015

DO - 10.1016/j.tecto.2014.01.015

M3 - Journal article

SN - 0040-1951

VL - 629

SP - 63

EP - 74

JO - Tectonophysics

JF - Tectonophysics

ER -

Low-temperature magnetic anisotropy in micas and chlorite

Abstract

Keywords

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