[S-IT27] 地球内部での液体の特性とその役割

[SIT27-01] Understanding of low velocity anomaly in the asthenosphere inferred from elastic wave velocity measurement of partially molten rocks

*大橋 智典¹、坂巻 竜也¹、久野 直毅¹、肥後 祐司²、柴崎 裕樹³、鈴木 昭夫¹ (1.東北大学大学院理学系研究科、2.(財)高輝度光科学センター、3.東北大学　学際科学フロンティア研究所)

キーワード：部分溶融、弾性波速度、アセノスフェア

The low velocity anomaly at the top of asthenosphere is one of important seismological features, and expected to be formed by carbon dioxide (CO₂)-induced partial melting of mantle rock. For better constraint on the melt fraction and distribution in the low-velocity zone, a comparison between experimental velocity and geophysical observation is a straightforward approach. Here we have measured the elastic wave velocity of olivine + carbonate melt using in-situ ultrasonic technique under conditions relevant to the top of asthenosphere. Both of compressional (V_P) and shear (V_S) wave velocities became smaller with increasing the volume fraction of melt in the sample, and we found quantitatively the velocity attenuation as a function of melt fraction. Comparing with the low-velocity zone, we succeeded in understanding a suitable amount of melt in the asthenosphere. The presence of magmas below the lithosphere could serve as a lubricant for the dynamics of plate tectonics and be a magma source of petit-spot volcanoes located at the outer rise of the oceanic plate.