[S-EM16] Geomagnetism, paleomagnetism, and rock magnetism

[SEM16-P08] Absolute paleointensity variations during the geomagnetic reversal and excursion recorded in lava sequences in the Afar Depression, Ethiopia

*Nobutatsu Mochizuki¹, Ryuichiro Hidaka², Chie Kato³, Tesfaye Kidane⁴, Ameha Atnafu Muluneh^5,6, Naoto Ishikawa⁷ (1.Department of Earth and Environmental Science, Faculty of Advanced Science and Technology, Kumamoto University, 2.Department of Earth and Environmental Science, Graduate School of Science and Technology, Kumamoto University, 3.Kyushu University, 4.Wayne State University, 5.Addis Ababa University, 6.GFZ German Research Centre for Geosciences, 7.University of Toyama)

Keywords:geomagnetic reversal, excursion, paleointensity, Tsunakawa-Shaw method, Afar, lava sequence

Geomagnetic reversals and excursions are characterized by a large fluctuation (decrease) in the Earth's magnetic field strength. Therefore, to understand the characteristics of geomagnetic field variations during the reversals and excursions, it is important to reconstruct not only paleomagnetic direction but also absolute paleomagnetic intensity. In this study, lava sequences in the Tendaho Graben in Afar were collected to reconstruct the geomagnetic field variations during the geomagnetic reversal and excursion. The previous results has provided the distribution of paleomagnetic polarity of lavas in the Tendaho Graben. Therefore, in the 2022 survey, rock samples were collected from two sections of lava sequence that may record the Matuyama-Brunhes polarity reversal. We also sampled a section of lava sequence which contain an excursion record of 0.65 ± 0.10 Ma. From Section 1, the paleomagnetic polarity changes of reverse-normal-reverse were obtained. The obtained paleomagnetic intensities are lower than the mean at the first reverse polarity. Subsequently, the paleointensities increased to 24–42 microT at the normal polarity, Finally, the paleointensities reduced to 4–5 microT. These paleomagnetic behaviors suggest the 18 lavas in section 1 recorded the beginning of the Matuyama-Brunhes polarity reversal. The five lavas in Section 3 yielded intermediate paleomagnetic directions and very weak paleomagnetic intensities of 4–11 µT.