Does size matter? Statistical limits of paleomagnetic field reconstruction from small rock specimens

Berndt, Thomas; Muxworthy, Adrian R.; Fabian, Karl

doi:10.1002/2015jb012441

Cited by 45 publications

(67 citation statements)

References 18 publications

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“…A recent analytical approach by Berndt et al . [] of magnetite grain assemblages found that paleointensity errors exceeded 20% and paleodirectional errors exceeded 20° for net moments of ∼10 −15 −10 −14 Am 2 . In summary, three very different independent analyses by this study, Kirschvink [] and Berndt et al .…”

Section: The Need For Ultra‐high Sensitivity Moment Magnetometrymentioning

confidence: 99%

“…In summary, three very different independent analyses by this study, Kirschvink [] and Berndt et al . [] have found that natural samples should preserve paleomagnetically useful information down to natural remanent moments of 10 −15 −10 −14 Am 2 , 100–1000 times below that measurable with standard superconducting rock magnetometers.…”

Section: The Need For Ultra‐high Sensitivity Moment Magnetometrymentioning

confidence: 99%

“…An analytical study using Langevin theory for detrital remanent magnetization carried by single domain magnetite grains by Kirschvink [1981] estimated a minimum net moment of 6 3 10 214 Am 2 for grains with radii about twice those considered here and for maximum mean directional errors of 58. A recent analytical approach by Berndt et al [2016] of magnetite grain assemblages found that paleointensity errors exceeded 20% and paleodirectional errors exceeded 208 for net moments of $10 215 210 214 Am 2 . In summary, three very different independent analyses by this study, Kirschvink [1981] and Berndt et al [2016] have found that natural samples should preserve paleomagnetically useful information down to natural remanent moments of 10 215 210 214 Am 2 , 100-1000 times below that measurable with standard superconducting rock magnetometers.…”

Section: The Need For Ultra-high Sensitivity Moment Magnetometrymentioning

confidence: 99%

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Ultra-high sensitivity moment magnetometry of geological samples using magnetic microscopy

Lima

Weiss

2016

Geochem. Geophys. Geosyst.

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Useful paleomagnetic information is expected to be recorded by samples with moments up to three orders of magnitude below the detection limit of standard superconducting rock magnetometers. Such samples are now detectable using recently developed magnetic microscopes, which map the magnetic fields above room‐temperature samples with unprecedented spatial resolutions and field sensitivities. However, realizing this potential requires the development of techniques for retrieving sample moments from magnetic microscopy data. With this goal, we developed a technique for uniquely obtaining the net magnetic moment of geological samples from magnetic microscopy maps of unresolved or nearly unresolved magnetization. This technique is particularly powerful for analyzing small, weakly magnetized samples such as meteoritic chondrules and terrestrial silicate crystals like zircons. We validated this technique by applying it to field maps generated from synthetic sources and also to field maps measured using a superconducting quantum interference device (SQUID) microscope above geological samples with moments down to 10−15 Am2. For the most magnetic rock samples, the net moments estimated from the SQUID microscope data are within error of independent moment measurements acquired using lower sensitivity standard rock magnetometers. In addition to its superior moment sensitivity, SQUID microscope net moment magnetometry also enables the identification and isolation of magnetic contamination and background sources, which is critical for improving accuracy in paleomagnetic studies of weakly magnetic samples.

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Section: The Need For Ultra‐high Sensitivity Moment Magnetometrymentioning

confidence: 99%

Section: The Need For Ultra‐high Sensitivity Moment Magnetometrymentioning

confidence: 99%

Section: The Need For Ultra-high Sensitivity Moment Magnetometrymentioning

confidence: 99%

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Ultra-high sensitivity moment magnetometry of geological samples using magnetic microscopy

Lima

Weiss

2016

Geochem. Geophys. Geosyst.

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“…The authors estimated that when CZ islands cooled through 320°C, their diameter was ~8 nm, implying that an impractically large number of ~10 9 islands should be sampled in each XPEEM dataset to obtain statistically meaningful paleodirections and intensities (10 3 -10 4 islands are typically analyzed during a XPEEM experiment). This led Berndt et al (2016) to question the reliability of published paleomagnetic XPEEM data. However, they obtained this estimate assuming CZ islands formed through nucleation and growth, a process different from spinodal decomposition.…”

Section: Introductionmentioning

confidence: 99%

Meteorite cloudy zone formation as a quantitative indicator of paleomagnetic field intensities and cooling rates on planetesimals

Maurel

Weiss

Bryson

2019

Earth and Planetary Science Letters

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Metallic microstructures in slowly-cooled iron-rich meteorites reflect the thermal and magnetic histories of their parent planetesimals. Of particular interest is the cloudy zone, a nanoscale intergrowth of Ni-rich islands within a Ni-poor matrix that forms below ~350°C by spinodal decomposition. The sizes of the islands have long been recognized as reflecting the lowtemperature cooling rates of meteorite parent bodies. However, a model capable of providing quantitative cooling rate estimates from island sizes has been lacking. Moreover, these islands are also capable of preserving a record of the ambient magnetic field as they grew, but some of the key physical parameters required for recovering reliable paleointensity estimates from magnetic measurements of these islands have been poorly constrained. To address both of these issues, we present a numerical model of the structural and compositional evolution of the cloudy zone as a function of cooling rate and local composition. Our model produces island sizes that are consistent with present-day measured sizes. This model enables a substantial improvement in the calibration of paleointensity estimates and associated uncertainties. In particular, we can now accurately quantify the statistical uncertainty associated with the finite number of islands acquiring the magnetization and the uncertainty on their size at the time of the record. We use this new understanding to revisit paleointensities from previous pioneering paleomagnetic studies of cloudy zones. We show that these could have been overestimated by up to one order of magnitude but nevertheless still require substantial magnetic fields to have been present on their parent bodies.Our model also allows us to estimate absolute cooling rates for meteorites that cooled slower than < 10,000°C My -1 . We demonstrate how these cooling rate estimates can uniquely constrain the low-temperature thermal history of meteorite parent bodies. Using the main-group pallasites as an example, we show that our results are consistent with the previously-proposed unperturbed, conductive cooling at low temperature of a ~200-km radius main-group pallasite parent body.

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“…Further, if we achieve 1 × 10 −16 Am 2 corresponding to an ~59-nm cube of magnetite, it is enough for most paleomagnetic studies because the SP/SD boundary of magnetite is around 15-50 nm (e.g., Newell and Merrill On the other hand, we may need to think about the stability of magnetic moment carried by a sample with small magnetic moment (Berndt et al 2016). Kirschvink et al (2015) reported the best sensitivity for a 2G SRM is ~10 −13 Am 2 using ultraclean quartz glass sample holder.…”

Section: −15mentioning

confidence: 99%

Scanning SQUID microscope system for geological samples: system integration and initial evaluation

Oda

Kawai

Miyamoto

et al. 2016

Earth Planets Space

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We have developed a high-resolution scanning superconducting quantum interference device (SQUID) microscope for imaging the magnetic field of geological samples at room temperature. In this paper, we provide details about the scanning SQUID microscope system, including the magnetically shielded box (MSB), the XYZ stage, data acquisition by the system, and initial evaluation of the system. The background noise in a two-layered PC permalloy MSB is approximately 40-50 pT. The long-term drift of the system is approximately ≥1 nT, which can be reduced by drift correction for each measurement line. The stroke of the XYZ stage is 100 mm × 100 mm with an accuracy of ~10 µm, which was confirmed by laser interferometry. A SQUID chip has a pick-up area of 200 μm × 200 μm with an inner hole of 30 μm × 30 μm. The sensitivity is 722.6 nT/V. The flux-locked loop has four gains, i.e., ×1, ×10, ×100, and ×500. An analog-to-digital converter allows analog voltage input in the range of about ±7.5 V in 0.6-mV steps. The maximum dynamic range is approximately ±5400 nT, and the minimum digitizable magnetic field is ~0.9 pT. The sensor-to-sample distance is measured with a precision line current, which gives the minimum of ~200 µm. Considering the size of pick-up coil, sensor-to-sample distance, and the accuracy of XYZ stage, spacial resolution of the system is ~200 µm. We developed the software used to measure the sensor-to-sample distance with line scan data, and the software to acquire data and control the XYZ stage for scanning. We also demonstrate the registration of the magnetic image relative to the optical image by using a pair of point sources placed on the corners of a sample holder outside of a thin section placed in the middle of the sample holder. Considering the minimum noise estimate of the current system, the theoretical detection limit of a single magnetic dipole is ~1 × 10 −14 Am 2 . The new instrument is a powerful tool that could be used in various applications in paleomagnetism such as ultrafine-scale magnetostratigraphy and single-crystal paleomagnetism.

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Does size matter? Statistical limits of paleomagnetic field reconstruction from small rock specimens

Cited by 45 publications

References 18 publications

Ultra-high sensitivity moment magnetometry of geological samples using magnetic microscopy

Ultra-high sensitivity moment magnetometry of geological samples using magnetic microscopy

Meteorite cloudy zone formation as a quantitative indicator of paleomagnetic field intensities and cooling rates on planetesimals

Scanning SQUID microscope system for geological samples: system integration and initial evaluation

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