日本地球惑星科学連合2018年大会

講演情報

[EE] ポスター発表

セッション記号 S (固体地球科学) » S-IT 地球内部科学・地球惑星テクトニクス

[S-IT22] 核-マントルの相互作用と共進化

2018年5月22日(火) 10:45 〜 12:15 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:飯塚 毅(東京大学)、渋谷 秀敏(熊本大学大学院先端科学研究部基礎科学部門地球環境科学分野)、土屋 卓久(愛媛大学地球深部ダイナミクス研究センター、共同)、太田 健二(東京工業大学大学院理工学研究科地球惑星科学専攻)

[SIT22-P29] Rock-magnetic properties of single zircon crystals sampled from the Yangtze River and the Mississippi River

*佐藤 雅彦1山本 伸次2山本 裕二3Du Wei1大野 正夫4綱川 秀夫5丸山 茂徳5 (1.東京大学、2.横浜国立大学、3.高知大学、4.九州大学、5.東京工業大学)

キーワード:Zircon、Rock-magnetism、Yangtze river、Mississippi river

Geomagnetic field paleointensity data provide critical information about the thermal evolution of the Earth, and the state of the geomagnetic field is closely related to the surface environment. While it is pivotal to understand the variations in geomagnetic field intensity throughout the history of the Earth, data are still too scarce to resolve billion-year-scale geomagnetic field variation. This is primarily because of the lack of geological samples for older eras, which often result in unsuccessful paleointensity experiments. In this study, we focus on a paleointensity experiment using single zircon crystal. Zircon crystals play an important role in paleomagnetic studies because they have several mineralogical advantages: (1) they commonly occur in crustal rocks, (2) precise age determinations with U–Th–Pb and (U–Th)/He analyses are possible, and (3) they have highly resilient responses to alterations and metamorphism.

In order to evaluate the feasibility of the paleointensity experiment using single zircon crystals, we conducted systematic rock-magnetic measurements for single zircon crystals sampled from the Yangtze River and the Mississippi River. Remanent magnetizations of the single zircon crystals were measured using the superconducting quantum interference device magnetometer. Natural remanent magnetization (NRM) intensity was first measured. Then low-temperature demagnetization (LTD) treatment was further conducted, and the memory (NRM intensity after LTD treatment) was measured. We also carried out alternating field demagnetization (AFD) treatment, and the memory (NRM intensity after AFD treatment) was measured. After the NRM measurements, isothermal remanent magnetization (IRM) was imparted with a field of 1 T using pulse magnetizer, and the resultant IRM intensity was measured. Subsequently, IRM intensity after LTD treatment and AFD treatment were measured. For selected samples, hysteresis loop and low-temperature remanence curves were measured using the alternating gradient magnetometer and the magnetic property measurement system. We will discuss the rock-magnetic properties of single zircon crystal based on the experimental results.