[S-IT22] 核-マントルの相互作用と共進化

[SIT22-10] Sound velocities of CaSiO₃ perovskite and some implications for deep mantle mineralogy

*入舩 徹男¹、グロー スティーブ¹ (1.愛媛大学地球深部ダイナミクス研究センター)

キーワード：マントル遷移層、下部マントル、弾性波速度

We have measured sound velocities of CaSiO₃ perovskitel (CaPv) under the entire pressure and temperature conditions of the mantle transition region by a combination of in situ X-ray observations and ultrasonic measurements in multi-anvil apparatus. Elastic properties of both tetragonal and cubic forms of CaPv have been obtained, yielding the shear modulus of cubic CaPv substantially lower than the theoretically predicted value. The present results, combined with the corresponding elastic properties of other high-pressure forms of major minerals in the mantle and subducting slabs, suggest the exsitence of a harzburgite-rich region near the bottom of the mantle transition region. In contrast, basaltic compositions should have significantly lower shear velocities relative to the surrounding pyrolitic mantle, and may explain the low velocity region atop of the lower mantle and the seismic scatterers in the uppermost lower mantle.