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Inter-laboratory calibration of low-field magnetic and anhysteretic susceptibility measurements

Inter-laboratory calibration of low-field magnetic and anhysteretic susceptibility measurements
Inter-laboratory calibration of low-field magnetic and anhysteretic susceptibility measurements
Inter-laboratory and absolute calibrations of rock magnetic parameters are fundamental for grounding a rock magnetic database and for semi-quantitative estimates about the magnetic mineral assemblage of a natural sample. Even a dimensionless ratio, such as anhysteretic susceptibility normalized by magnetic susceptibility (Ka/K) may be biased by improper calibration of one or both of the two instruments used to measure Ka and K. In addition, the intensity of the anhysteretic remanent magnetization (ARM) of a given sample depends on the experimental process by which the remanence is imparted. We report an inter-laboratory calibration of these two key parameters, using two sets of artificial reference samples: a paramagnetic rare earth salt, Gd2O3 and a commercial "pozzolanico" cement containing oxidized magnetite with grain size of less than 0.1 m according to hysteresis properties. Using Gd2O3 the 10 Kappabridges magnetic susceptibility meters (AGICO KLY-2 or KLY-3 models) tested prove to be cross-calibrated to within 1%. On the other hand, Kappabridges provide a low-field susceptibility value that is ca. 6% lower than the tabulated value for Gd2O3, while average high-field susceptibility values measured on a range of instruments are indistinguishable from the tabulated value. Therefore, we suggest that Kappabridge values should be multiplied by 1.06 to achieve absolute calibration. Bartington Instruments magnetic susceptibility meters with MS2B sensors produce values that are 2–13% lower than Kappabridge values, with a strong dependence on sample centering within the sensor. The Ka/K ratio of ca. 11, originally obtained on discrete cement samples with a 2G Enterprises superconducting rock magnetometer and a KLY-2, is consistent with reference parameters for magnetites of grain size <0.1 m. On the other hand, Ka values from a 2G Enterprises magnetometer and K values from a Bartington Instruments MS2C loop sensor for u-channel and discrete cement samples, will produce average Ka/K values that are unrealistically high if not properly corrected for the nominal volume detected by the sensors for these instruments. Inter-laboratory measurements of K and Ka for standard paleomagnetic plastic cubes filled with cement indicate remarkable differences in the intensity of the newly produced ARMs (with a standard deviation of ca. 21%), that are significantly larger than the differences observed from the calibration of the different magnetometers employed in each laboratory. Differences in the alternating field decay rate are likely the major source of these variations, but cannot account for all the observed variability. With such large variations in experimental conditions, classical interpretation of a "King plot" of Ka versus K would imply significant differences in the determination of grain size of magnetite particles on the same material.
rock magnetism, magnetic susceptibility, anhysteretic remanent magnetization, calibration, instrumentation, relative paleointensity
0031-9201
25-38
Sagnotti, L.
c9bacb8c-1e84-4719-9f62-0989ec640f3b
Rochette, P.
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Jackson, M.
f73553de-6f67-41c2-9f3d-613b61a00d80
Vadeboin, F.
fefe713e-2da1-4c73-b1d4-45aaed30d343
Dinares-Turell, J.
1ed0d59e-90de-4704-aa3d-2f57580c5a4a
Winkler, A.
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Larrasoana, J.C.
9201c9da-a9fc-4f3b-86a8-83fda450084e
O'Regan, M.
83b80486-4e18-4089-9b12-361232727095
Roberts, A.P.
4497b436-ef02-428d-a46e-65a22094ba52
Sagnotti, L.
c9bacb8c-1e84-4719-9f62-0989ec640f3b
Rochette, P.
0f95d768-6395-4c89-adb2-4f1ef6ce07fd
Jackson, M.
f73553de-6f67-41c2-9f3d-613b61a00d80
Vadeboin, F.
fefe713e-2da1-4c73-b1d4-45aaed30d343
Dinares-Turell, J.
1ed0d59e-90de-4704-aa3d-2f57580c5a4a
Winkler, A.
e4c7ee1b-720f-4fcf-9375-cea81d063e90
Larrasoana, J.C.
9201c9da-a9fc-4f3b-86a8-83fda450084e
O'Regan, M.
83b80486-4e18-4089-9b12-361232727095
Roberts, A.P.
4497b436-ef02-428d-a46e-65a22094ba52

Sagnotti, L., Rochette, P., Jackson, M., Vadeboin, F., Dinares-Turell, J., Winkler, A., Larrasoana, J.C., O'Regan, M. and Roberts, A.P. (2003) Inter-laboratory calibration of low-field magnetic and anhysteretic susceptibility measurements. Physics of the Earth and Planetary Interiors, 138 (1), 25-38. (doi:10.1016/S0031-9201(03)00063-3).

Record type: Article

Abstract

Inter-laboratory and absolute calibrations of rock magnetic parameters are fundamental for grounding a rock magnetic database and for semi-quantitative estimates about the magnetic mineral assemblage of a natural sample. Even a dimensionless ratio, such as anhysteretic susceptibility normalized by magnetic susceptibility (Ka/K) may be biased by improper calibration of one or both of the two instruments used to measure Ka and K. In addition, the intensity of the anhysteretic remanent magnetization (ARM) of a given sample depends on the experimental process by which the remanence is imparted. We report an inter-laboratory calibration of these two key parameters, using two sets of artificial reference samples: a paramagnetic rare earth salt, Gd2O3 and a commercial "pozzolanico" cement containing oxidized magnetite with grain size of less than 0.1 m according to hysteresis properties. Using Gd2O3 the 10 Kappabridges magnetic susceptibility meters (AGICO KLY-2 or KLY-3 models) tested prove to be cross-calibrated to within 1%. On the other hand, Kappabridges provide a low-field susceptibility value that is ca. 6% lower than the tabulated value for Gd2O3, while average high-field susceptibility values measured on a range of instruments are indistinguishable from the tabulated value. Therefore, we suggest that Kappabridge values should be multiplied by 1.06 to achieve absolute calibration. Bartington Instruments magnetic susceptibility meters with MS2B sensors produce values that are 2–13% lower than Kappabridge values, with a strong dependence on sample centering within the sensor. The Ka/K ratio of ca. 11, originally obtained on discrete cement samples with a 2G Enterprises superconducting rock magnetometer and a KLY-2, is consistent with reference parameters for magnetites of grain size <0.1 m. On the other hand, Ka values from a 2G Enterprises magnetometer and K values from a Bartington Instruments MS2C loop sensor for u-channel and discrete cement samples, will produce average Ka/K values that are unrealistically high if not properly corrected for the nominal volume detected by the sensors for these instruments. Inter-laboratory measurements of K and Ka for standard paleomagnetic plastic cubes filled with cement indicate remarkable differences in the intensity of the newly produced ARMs (with a standard deviation of ca. 21%), that are significantly larger than the differences observed from the calibration of the different magnetometers employed in each laboratory. Differences in the alternating field decay rate are likely the major source of these variations, but cannot account for all the observed variability. With such large variations in experimental conditions, classical interpretation of a "King plot" of Ka versus K would imply significant differences in the determination of grain size of magnetite particles on the same material.

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More information

Published date: 2003
Keywords: rock magnetism, magnetic susceptibility, anhysteretic remanent magnetization, calibration, instrumentation, relative paleointensity

Identifiers

Local EPrints ID: 11171
URI: https://eprints.soton.ac.uk/id/eprint/11171
ISSN: 0031-9201
PURE UUID: bd200f87-cc4b-47e3-9a58-e3170ed77e8e

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Date deposited: 28 Oct 2004
Last modified: 17 Jul 2017 17:04

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