[P-PS07] Planetary Sciences

[PPS07-11] Intensity of the ancient Martian magnetic field estimated from the strong magnetic anomaly data: strong or weak dynamo field?

*Masahiko Sato¹, Masashi Ushioda², Ryoichi Nakada³, Yujiro Tamura⁴, Shinji Yamamoto⁴, Kazuhito Ozawa¹, Futoshi Takahashi⁵ (1.The University of Tokyo, 2.Shikoku Research Institute Inc., 3.Japan Agency for Marine-Earth Science and Technology, 4.Yokohama National University, 5.KyushuUniversity)

Keywords:Mars, Magnetic anomaly, Ancient Martian magnetic field, Rock-magnetism, Plagioclase

Magnetic field observations by the Mars Global Surveyor revealed that there are strong magnetic anomalies originating from the crustal remanences (Acuna et al. 1999, Science), which is estimated to be about 10 times as strong as the Earth’s crustal magnetization (Voorhies et al., 2002, JGR). Plagioclase crystals sometimes contain fine-grained magnetite inclusions as the results of exsolution at subsolidus condition (Feinberg et al., 2005, Geology), and the natural remanent magnetization carried by the exsolved magnetite crystals in plagioclase is most likely candidate of the source of strong magnetic anomaly in terms of the remanence stability and crystallization process (Sato et al. 2018, GRL). In this study, to estimate the paleo-planetary field intensity of Mars based on the crustal remanence records, magnetic measurements combined with microscopic observation and synchrotron radiation study were conducted for plagioclase crystals contained in natural mafic-plutonic rocks. The measurement sequence of the single-grain plagioclase crystal was as follows: (1) a magnetic hysteresis loop measurement using an Alternating Gradient Magnetometer, (2) an L_III-edge X-ray absorption near edge structure (XANES) measurement at synchrotron radiation facilities, and (3) a microscopic observation using electron microprobes. Additionally, a suite of remanence acquisition/demagnetization experiments were conducted for the assemblages of plagioclase crystals to evaluate the remanence acquisition efficiency of exsolved magnetite crystals. On the basis of the experimental results and the crustal remanence observations, we will discuss the paleo-planetary field intensity of Mars.