HR: 16:00h
AN: U44A-01    [Abstracts]
TI: Determination of post-perovskite phase transition boundary in MgSiO₃ up to 4400 K and implications for thermal structure at the base of the mantle
AU: * Tateno, S
EM: tateno.s.aa@m.titech.ac.jp
AF: Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8551, Japan
AU: Hirose, K
EM: kei@geo.titech.ac.jp
AF: Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8551, Japan
AU: Hirose, K
EM: kei@geo.titech.ac.jp
AF: Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Kanagawa, 237-0061, Japan
AU: Sata, N
EM: sata@jamstec.go.jp
AF: Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Kanagawa, 237-0061, Japan
AU: Ohishi, Y
EM: ohishi@spring8.or.jp
AF: Japan Synchrotron Radiation Research Institute, Sayo-cho, Hyogo, 679-5198, Japan
AB: Thermal structure within the D" layer is of great significance because it determines the rheology and thus the dynamics in the D" and modulates the heat flow out of the outer core. A newly discovered post-perovskite phase transition can provide tighter constraint on the thermal structure within the D" based on the idea "double- crossing". In the thermal boundary layer, a steep geotherm is likely to intersect the post-perovskite phase transition boundary twice, which is supported by the presence of paired seismic discontinuities. Since this model strongly depends on the phase transition boundary, it should be determined more precisely. Here we conducted the phase equilibria experiments on MgSiO₃ at a much wider range of PT conditions, 113-170 GPa and 2500-4400 K, in order to refine the post-perovskite phase transition boundary on the basis of synchrotron X-ray diffraction measurements in situ at high-pressure and -temperature in a laser-heated diamond-anvil cell. Both MgO and gold were used as internal pressure standards. Argon was loaded as a pressure medium and thermal insulation. Post-perovskite phase transition boundary was determined in both the forward and reverse directions. Our results show that the Clapeyron slope is larger than +11.5 MPa/K (Hirose et al., 2006 GRL) based on MgO scale and that resultant phase transition temperature at the CMB pressure is about 3300 K. This observation implies that even moderate temperature gradient in the D" could cause double-crossing.
DE: 3620 Mineral and crystal chemistry (1042)
DE: 3621 Mantle processes (1038)
DE: 3630 Experimental mineralogy and petrology
SC: Union [U]
MN: 2007 Fall Meeting