[S-EM13] Geomagnetism, paleomagnetism and rock magnetism

[SEM13-P12] Preliminary results of rock magnetic properties from oceanic core complexes in the Philippine Sea: Implication for magnetization structure of oceanic lithosphere

*Masakazu Fujii^1,2, Yasuhiko Ohara^3,4,5, Yumiko Harigane⁶, Hiroyuki Yamashita⁷, Kyoko Okino⁸ (1.National Institute of Polar Research, 2.SOKENDAI (The Graduate University for Advanced Studies), 3.Hydrographic and Oceanographic Department of Japan, 4.Japan Agency for Marine-Earth Science and Technology, 5.Nagoya University, 6.Geological Survey of Japan, AIST, 7.Kanagawa Prefectural Museum of Natural History, 8.Atmosphere and Ocean Research Institute, The University of Tokyo)

Keywords:rock magnetics, oceanic lithoshepre, oceanic core complex, Philippine Sea

Marine magnetic anomalies have been utilized to understand geomagnetic field reversals and fluctuations, providing valuable insights into Earth's tectonics, including the origin of the ocean floor. The accumulation of magnetic data at the sea surface and advances in near-bottom surveys provide further insights into oceanic lithosphere processes such as crustal accretion, faulting, hydrothermal circulation, and water-rock reaction. However, the relationship between the anomaly signal and geological ground truth remains poorly understood. In particular, rock magnetic data of oceanic lower crustal and mantle are limited due to sampling difficulties.

Here, we present new rock magnetic data studied on oceanic core complexes in the Philippine Sea. The samples were collected from abyssal outcrops of Mado, Tosa, and Sanuki Megamullions during Japanese research expeditions aboard the R/V Yokosuka and R/V Hakuho-maru; YK18-07, YK19-04S, YK20-18S, YK21-06S, YK22-18S, YK23-05S, KH-07-02, KH-18-02. Most samples were collected using the submersible Shinkai6500. Part of the basaltic rocks are highly magnetized with a natural remanent magnetization of up to 25 A/m, known as the primary magnetic source of the oceanic lithosphere. Results from ultramafic rocks show a negative correlation between grain density and magnetic properties. Furthermore, it is evident that highly serpentinized peridotite with low density is mostly magnetic with strong remanent magnetization (up to 6 A/m), but also includes a variety of weak to intermediate properties. Results from the gabbroic rocks indicate that oxide gabbro has high magnetic susceptibility, and its induced magnetization (up to 10 A/m) may significantly contribute to marine magnetic anomalies.