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

• Published in: Journal of geophysical research. Solid earth Vol. 121; no. 1; pp. 15 - 26
• Main Authors: Berndt, Thomas, Muxworthy, Adrian R., Fabian, Karl
• Format: Journal Article
• Language: English
• Published: 01.01.2016
• Subjects: cloudy zone; error analysis; nanopaleomagnetism; single crystal; statistical thermodynamics
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1002/2015JB012441

As samples of ever decreasing sizes are being studied paleomagnetically, care has to be taken that the underlying assumptions of statistical thermodynamics (Maxwell‐Boltzmann statistics) are being met. Here we determine how many grains and how large a magnetic moment a sample needs to have to be able to accurately record an ambient field. It is found that for samples with a thermoremanent magnetic moment larger than 10−11Am2 the assumption of a sufficiently large number of grains is usually given. Standard 25 mm diameter paleomagnetic samples usually contain enough magnetic grains such that statistical errors are negligible, but “single silicate crystal” works on, for example, zircon, plagioclase, and olivine crystals are approaching the limits of what is physically possible, leading to statistic errors in both the angular deviation and paleointensity that are comparable to other sources of error. The reliability of nanopaleomagnetic imaging techniques capable of resolving individual grains (used, for example, to study the cloudy zone in meteorites), however, is questionable due to the limited area of the material covered. Key Points Paleofields from single crystals have small additional errors due to their small number of particles Nanomagnetic imaging of cloudy zones of meteorites does not allow conclusions about the paleofield Average intensity centimeter‐size samples usually contain enough magnetic particles to be accurate recorders