[S-EM19] Earth and planetary magnetism: Observations, modeling, and implications on dynamics and evolution

[SEM19-P02] Paleomagnetic study on the transitionally magnetized volcanic rocks from the Tahaa Island, French Polynesia

*Yuhji Yamamoto¹, Kenneth A Hoffman², Myriam Annie Claire Kars¹ (1.Center for Advanced Marine Core Research, Kochi University, 2.California Polytechnic State University)

Volcanic rocks collected from the Society Islands, French Polynesia, were systematically investigated in terms of paleomagnetism and geochronology (Yamamoto et al., 2002; Yamamoto and Tsunakawa, 2005; Uto et al., 2007). Some sites were found to be transitionally magnetized, and the follow-up laser-heating ⁴⁰Ar/³⁹Ar dating and additional palaeomagnetic measurements were conducted on samples from these sites in Yamamoto et al. (2007): a lava sequence in the Tahaa Island consisting of the four consecutive lava flows (TA04, 05, 06 and 07) gave the average virtual dipole moments (VDMs) of ~ 5 ZAm2 and the Ar/Ar age of 3.20 +/- 0.03 Ma. This age is consistent with the upper boundary age of the Mammoth reversed subchron in GPTS2012 (3.207 Ma; Ogg et al., 2012).

To further characterize the paleomagnetic behavior recorded in the lava sequence, a follow-up sampling was done in 2014. We collected ~50 new mini-core samples from the sequence, and in addition, 10 new mini-core samples were drilled from a single lava flow of a vicinity lava sequence, which corresponds to the site TA01 in the previous study (K-Ar age of 3.14 +/- 0.06 Ma; Uto et al., 2007). These mini-core samples were cut into specimens and they were subjected to paleomagnetic measurements including the Tsunakawa-Shaw absolute paleointensity experiments. We will report these results together with the previous results which are reanalyzed by a latest scheme.