5:15 PM - 6:45 PM
[SEM13-P02] Investigation of the carriers of secondary magnetization using micro-magnetic analysis with SQUID microscopy
Keywords:Paleomagnetism, Secondary magnetization
Marine successions distributed in the Boso Peninsula are suitable for paleomagnetic studies because these samples contain abundant magnetic minerals and retain stable paleomagnetic signals. However, there are cases in which the presence of ferromagnetic iron sulfides such as greigite (Oda et al., 2022) or low-temperature, high-coercivity components (Konishi and Okada, 2020) is indicated. In these cases, the conventionally used progressive thermal demagnetization (pThD) or progressive alternating field demagnetization (pAFD) may not be sufficient to remove secondary magnetization. Recently, Hybrid demagnetization (HyD), which combines both demagnetization methods, has been used to remove secondary magnetization. However, the carrier of the secondary magnetization removed by HyD has rarely been identified, and in most cases, it has been estimated indirectly by rock magnetic experiments. Therefore, the degree of loss of secondary magnetization due to the hybrid method has not been quantitatively evaluated, and the evaluation of HyD as a method is still insufficient. We are not able to deny the possibility that the hybrid method may affect the principal component analysis and the calculation of relative paleointensity. Therefore, it is important to conduct demagnetization experiments by mapping the magnetization of each magnetic mineral to the results of electron microscopic observations and EDS analysis.
In this presentation, we report preliminary results of electron microscopy and EDS analysis to identify carriers of secondary magnetization and micro-magnetic analysis by SQUID microscopy to determine the magnetization of magnetic minerals.
As of now, we have thermally demagnetized siltstone samples of the Mera Formation, Chikura Group in the southernmost part of the Boso Peninsula at ~300°C and AFD at 5 mT and 15 mT after ThD. The dipole approximations of one of the dipole magnetic anomalies show paleomagnetic direction, similar to secondary magnetization demagnetized at low-temperatures below 300℃. We plan to proceed with pAFD at 20 mT to 50 mT, which corresponds to the primary component, and conduct electron microscopic observations and EDS analysis at higher resolution with osmium coating on the thin section.
References
Konishi, T., Okada, M. (2020). PEPS, 7:35. Doi: 10.1186/s40645-020-00352-0. Oda, H., Nakazato, H., Nanayama, F., Harigane, Y. (2022). EPS, 74:80. Doi: 10.1186/s40623-022-01626-1.
In this presentation, we report preliminary results of electron microscopy and EDS analysis to identify carriers of secondary magnetization and micro-magnetic analysis by SQUID microscopy to determine the magnetization of magnetic minerals.
As of now, we have thermally demagnetized siltstone samples of the Mera Formation, Chikura Group in the southernmost part of the Boso Peninsula at ~300°C and AFD at 5 mT and 15 mT after ThD. The dipole approximations of one of the dipole magnetic anomalies show paleomagnetic direction, similar to secondary magnetization demagnetized at low-temperatures below 300℃. We plan to proceed with pAFD at 20 mT to 50 mT, which corresponds to the primary component, and conduct electron microscopic observations and EDS analysis at higher resolution with osmium coating on the thin section.
References
Konishi, T., Okada, M. (2020). PEPS, 7:35. Doi: 10.1186/s40645-020-00352-0. Oda, H., Nakazato, H., Nanayama, F., Harigane, Y. (2022). EPS, 74:80. Doi: 10.1186/s40623-022-01626-1.