The Culprit of Bias in the Shaw-type Method of Estimating Geomagnetic Paleointensity and an Innovative Computational Method for Enhanced Reliability

作者：Kaixian Qi, Shuhui Cai, Huafeng Qin, Chenglong Deng, Yongxin Pan, Yuhji Yamamoto, Xin Cheng, Hanning Wu, Rixiang Zhu · 年份：2024 · DOI：10.5194/egusphere-egu24-9314 · 研究领域：Geomagnetism and Paleomagnetism Studies、Geophysical and Geoelectrical Methods、Earthquake Detection and Analysis

Retrieving precise information about the ancient geomagnetic field strength (paleointensity) is crucial for understanding the Earth's interior evolution. The Shaw-type method is one of the major protocols used to estimate paleointensity, characterized by relatively expeditious processes and high success rates. However, albeit employing strict selection criteria, Shaw-type paleointensity results occasionally exhibit bias, necessitating further methodological development. Despite the significance of identifying the causes of these biased estimates, there has been limited detailed discussion on this issue.To clarify the culprit of bias in Shaw-type paleointensity, we conducted a pseudo-Tsunakawa-Shaw experiment using Permian basalts from the Tarim large igneous province (TLIP). In this experiment, the "NRMs (natural remanent magnetizations)" of the samples were acquired in a controlled lab field. We then monitored changes in various rock magnetic parameters, such as squareness (Mrs/Ms), coercivity (Bc), ARM, amtLTD (amount of remanence demagnetized by low-temperature treatment), MDF (median destructive field), and R (the ratio of thermal remanent magnetization (TRM) to anhysteretic remanent magnetization (ARM)), before and after heating, and compared them to the recovered paleointensities.Our analysis uncover a proportional relationship between changes in R and the bias in paleointensity, likely attributed to variations in grain sizes. Combining with microscopic observations, we...