Paleomagnetism Calibration Standards for Rock Magnetometers
Abstract
The changing orientations and magnitudes of planetary magnetic fields are recorded by rocks as three-dimensional (3D) magnetization vectors. To retrieve these records, paleomagnetists typically use 3D magnetometers capable of physically rotating samples through multiple orientations and/or measuring along more than one axis with multiple sets of SQUID pickup coils. These devices are calibrated and tuned electronically during manufacture, but rigorous recalibration has presented a challenge due to the lack of a calibration standard with known composition and magnetic properties and behavior.
In lieu of a standard reference material (SRM), many paleomagnetism laboratories have developed their own internal references, from natural limestone cores to powdered basalt to commercial permanent magnets. Few of these materials meet more than a small subset of the requirements for an actual standard, including thermochemical stability, sufficiently high coercivity to resist unwanted remagnetization, and a traceable link to the SI. In contrast, a paleomagnetism SRM would enable instrument calibration relative to absolute magnetic moment and susceptibility, thereby improving the accuracy of measurements. This will ultimately reduce the deviation of remanent magnetization measurements between laboratories (σ = 3.4% among 12 labs (Sagnotti et al., 2003)). In this study, we first assess the viability of existing internal references and their procedures for use from > 20 laboratories to quantify the relationship between composition and reported long-term (≤ 18 years) remanence behavior. We then present a candidate suite of synthetic materials whose magnetic moments are within the natural rock range, including ferrites (e.g. Ti-substituted magnetite, Sr-ferrite) and NdFeB magnets, enabling us to test their ability to record and retain magnetization oriented in 3D space. Finally, we invite the broader community of paleomagnetism researchers to join our effort and lay the groundwork for interlaboratory testing.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMGP13A..26S
- Keywords:
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- 0699 General or miscellaneous;
- ELECTROMAGNETICSDE: 1594 Instruments and techniques;
- GEOMAGNETISM AND PALEOMAGNETISMDE: 1599 General or miscellaneous;
- GEOMAGNETISM AND PALEOMAGNETISMDE: 1714 Geomagnetism and paleomagnetism;
- HISTORY OF GEOPHYSICS