日本地球惑星科学連合2014年大会

講演情報

口頭発表

セッション記号 S (固体地球科学) » S-CG 固体地球科学複合領域・一般

[S-CG62_2AM2] 流体と沈み込み帯のダイナミクス

2014年5月2日(金) 11:00 〜 12:45 502 (5F)

コンビーナ:*岡本 敦(東北大学大学院環境科学研究科)、川本 竜彦(京都大学大学院理学研究科附属地球熱学研究施設)、片山 郁夫(広島大学大学院理学研究科地球惑星システム学専攻)、座長:川本 竜彦(京都大学大学院理学研究科附属地球熱学研究施設)、岡本 敦(東北大学大学院環境科学研究科)

12:30 〜 12:45

[SCG62-P01_PG] 圧力1GPaにおけるアンチゴライト蛇紋岩弾性波速度の温度依存性

ポスター講演3分口頭発表枠

*白井 亮1渡辺 了1米田 明2道林 克禎3 (1.富山大学理学部地球科学科、2.岡山大学地球物質科学研究センター、3.静岡大学理学部地球科学科)

キーワード:地震波速度, 蛇紋岩, アンチゴライト, 沈み込み帯, 流体

Serpentines play key roles in subduction zone processes including water transport, seismogenesis, exhumation of high-pressure rocks, etc. Geophysical mapping of serpentinized regions in the mantle wedge leads to further understanding of these processes. Seismic properties of serpentinized peridotites are critical to interpretation of seismological observations. Antigorite is a major form of serpentine, which is stable to higher temperatures. The single-crystal elastic properties were recently revealed via Brillouin scattering technique (Bezacier et al., 2010; 2013). However, the temperature dependence of elastic properties is still poorly understood. We have measured elastic wave velocities in a antigorite serpentinite at high temperature and pressure conditions.

A black massive antigorite serpentinite was collected from the Nagasaki metamorphic rocks, western Japan. It is composed of antigorite (98.0 vol.%), diopside (1.5 vol.%) and magnetite (0.5 vol.%). Microstructural observation reveals an interpenetrating texture characterized by randomly oriented antigorite blades. Antigorite CPO data shows weak concentration of antigorite axes. Elastic wave velocities measured at 180 MPa shows very weak anisotropy in elasticity. Cylindrical samples (D=L=6mm) were made with ultrasonic machining.

Measurements were made at the pressure of 1 GPa and the temperature of up to 550 C, by using a piston-cylinder type high pressure apparatus at ISEI, Okayama University. The pulse reflection technique was employed for velocity measurement. One LiNbO3 transducer with the resonant frequency of 5 MHz was used to transmit and receive ultrasonic signals. The length of the sample at high pressure and temperature conditions was estimated from the length of the recovered sample.

Both compressional and shear wave velocities linearly decrease with increasing temperature. The temperature derivatives are -3.6×10-4 (km/s/K) and -2.7×10-4 (km/s/K) for compressional and shear wave velocities, respectively. The temperature derivative of compressional wave velocity is close to that observed in the direction subparallel to antigorite c-axis (Yano et al., in prep.). The temperature dependence of c33 might dominate that of the effective elastic constants of a randomly oriented polycrystalline aggregate. Applications to seismological observations will also be discussed in this presentation.