Investigating the Accuracy, Precision, and Cooling Rate Dependence of Laboratory-Acquired Thermal Remanences During Paleointensity Experiments

Abstract

We examine the behavior of natural basaltic and trachytic samples during paleointensity experiments on both the original and laboratory-acquired thermal remanences and characterize the samples using proxies for domain state including curvature (k) and the bulk domain stability parameters of Paterson (2011, https://doi.org/10.1029/2011JB008369) and Paterson et al. (2017, https://doi.org/10.1073/pnas.1714047114), respectively. A curvature value of 0.164 (suggested by Paterson, 2011, https://doi.org/10.1029/2011JB008369) as a critical threshold that separates single-domain-like remanences from multidomain-like remanances on the original paleointensity data was used to separate samples into “straight” (single-domain-like) and “curved” (multidomain-like) groups. Specimens from the two sample sets were given a “fresh” thermal remanent magnetization in a 70 μT field and subjected to an infield-zerofield, zerofield-infield (IZZI)-type (Yu et al., 2004, https://doi.org/10.1029/2003GC000630) paleointensity experiment. The straight sample set recovered the laboratory field with high precision while the curved set had much more scattered results (70.5 ± 1.5 and 71.9 ± 5.2 μT, respectively). The average intensity of both sets for straight and curved was quite close to the laboratory field of 70 μT, however, suggesting that if experiments contain a sufficient number of specimens, there does not seem to be a large bias in the field estimate. We found that the dependence of the laboratory thermal remanent magnetization on cooling rate was significant in most samples and did not depend on domain states inferred from proxies based on hysteresis measurements and should be estimated for all samples whose cooling rates differ from that used in the laboratory.