[S-EM15] Geomagnetism, paleomagnetism and rock magnetism

[SEM15-04] Application of absolute paleointensity methods on aged thermoremanent magnetization and implications for fragile curvature in paleointensity plots

*Yuhji Yamamoto¹, Lisa Tauxe², Hyeon-Seon Ahn³, Christeanne Nicole Santos² (1.Center for Advanced Marine Core Research, Kochi University, 2.Scripps Institution of Oceanography, University of California San Diego, 3.Korea Institute of Geoscience and Mineral Resources)

Absolute paleointensity (API) of the geomagnetic field can be estimated from volcanic rocks by comparing the natural remanent magnetization (NRM) to a laboratory-induced thermoremanent magnetization (Lab-TRM). Plots of NRM unblocking vs Lab-TRM blocking from API experiments, so-called Arai plots, often exhibit non-ideal curvature which can result in biased estimates. We have targeted on specimens gave a ‘fresh’ Lab-TRMs in a 70 μT field and then aged for a few years. Tauxe et al. (2021) showed that curvature can increase with age, however, the CCRIT selection criteria designed to eliminate such behavior (Cromwell et al., 2015; Tauxe et al., 2016) yielded accurate API estimates by the IZZI Thellier method (Yu et al., 2004) for two-year aged specimens (70.3 ± 3.8 μT; N = 96 specimens out of 120 experiments). API can also be estimated in coercivity space, and the Tsunakawa-Shaw method yielded accurate API results (68.5 ± 4.5 μT; N=17 specimens out of 20 experiments) for four-year aged specimens by its selection criteria. In thermal API experiments, curvature is related to internal structure with more single-domain like behavior having the least curvature. Here we show that the fraction of anhysteretic remanent magnetization demagnetized by low-temperature treatment was larger for samples with larger thermal curvatures suggesting a magnetocrystalline anisotropy source. We also tested experimental remedies that have been proposed to improve the accuracy of paleointensity estimates. In particular we test the efficacy of the multi-specimen approach and a strategy pre-treating specimens with low field alternating field demag netization prior to the paleointensity experiment. Neither yielded accurate results.