[S-IT16] 地球深部科学

[SIT16-P10] Deformation experiments on NaNiF3 perovskite and post-perovskite

*山崎 大輔¹、生田 大穣¹、ロウ カヤン¹、リュウ カオ¹、芳野 極¹、辻野 典秀²、柿澤 翔²、肥後 祐司²、西原 遊³ (1.岡山大学、2.高輝度光科学研究センター、3.愛媛大学)

In the Earth’s lower mantle with increasing pressure, bridgmanite (perovskite structure) which is a most abundant mineral in the lower mantle transform into post-perovskite which is considered to be main constituting material in the D” layer. Core-mantle boundary is the greatest boundary in the Earth in terms of temperature gradient and chemical composition and it is the graveyard of the subducted slabs and root of the upwelling plumes. Because D” layer is just above core-mantle boundary, physical properties of post-perovskite is a fundamentally important. Viscosity is considered to be one of the most important property because it controls the flow rate and hence the viscosities of bridgmanite and post-perovskite are key factor to discuss the mantle convection in the deep lower mantle. Deformation experiments are useful method to estimate viscosity of materials, and therefore we conducted deformation experiments on NaNiF3 perovskite and post-perovskite as an analogue of MgSiO3 because stable pressure for MgSiO3 post-perovskite is >~120 GPa and it is impossible to perform deformation experiment at such high pressure at high temperature. Experiments were conducted by using D-111 deformation apparatus equipped with a Kawai-type assembly which enable us to generate higher pressure than 20 GPa which is enough high for NaNiF3 post-perovskite. During deformation, we observed the sample shape especially length as an X-ray radiography and obtained lattice constants by X-ray diffraction pattern and estimated strain rate and stress. Preliminary result suggests that viscosity of perovskite and post-perovskite is comparable within less than one order of magnitude. This indicates that the relatively uniform viscosity is expected in the lower mantle and D” layer. On the other hand, post-perovskite itself may have large variation of viscosity: If strong lattice preferred orientation of post-perovskite is formed during deformation at D” layer, flow direction dependent viscosity is likely obtained because post-perovskite is elastically anisotropic material. We would like to examine this in the future.