[S-IT27] Property and role of liquids inside the Earth

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

*Tomonori Ohashi¹, Tatsuya Sakamaki¹, Naoki Hisano¹, Yuji Higo², Yuki Shibazaki³, Akio Suzuki¹ (1.Department of Earth Science, Tohoku University, 2.Japan Synchrotron Radiation Research Institute, 3.Frontier Research Institute for Interdisciplinary Sciences, Tohoku University)

Keywords:partial melting, elastic wave velocity, asthenosphere

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.