Meeting room "Glova", 4 floor, Integrated Research Building
Abstract
Phase transitions of olivine to wadsleyite, ringwoodite, and perovskite (+periclase) have been considered to correspond to major seismic discontinuities in the mantle transition region (410 km, 520 km, 660 km discontinuity, respectively). Although a lot of efforts have been made to precisely determine the phase transition boundaries from in situ high-pressure X-ray experiments, it has been noted that the choice of pressure scale strongly influences on the resultant phase transition boundaries. Here we unified the pressure scales of MgO, Au, and NaCl based on self-consistent P-V-T relation of MgO determined by simultaneous ultrasonic and in situ X-ray measurement at both high pressures (up to 23.6 GPa) and high temperatures (up to 1650 K), which are comparable to those of the mantle transition region, and recalculated olivine-wadsleyite (Morishima et al., 1994; Katsura et al., 2004), wadsleyite-ringwoodite (Suzuki et al., 2000; Inoue et al., 2006), ringwoodite-perovskite (+MgO) (Irifune et al., 1998; Katsura et al., 2003; Fei et al., 2004) transition boudaries of Mg2SiO4 obtained by high-pressure in situ X-ray experiments using Au, NaCl, or MgO as a pressure standard. As a result of unification of pressure scale, we observed good agreement among these previous studies. In particular, serious disagreements have been reported among the studies of the ringwoodite-perovskite transition boundaries in Mg2SiO4 determined by using Au (Irifune et al., 1998; Katsura et al., 2003) and MgO (Fei et al., 2004) pressure scales. The unified pressure scale yields good agreement in the phase transition boundary between Katsura et al. (2003) and Fei et al. (2004), although recalculated phase transition boundary based on the result of Irifune et al. (1998) shows slightly lower phase transition pressures. The unified ringwoodite-perovskite transition boundaries in Mg2SiO4 locates at ~23 GPa at 1600℃, which is only marginally lower than that of the 660 km discontinuity.
For inquiry：Taku Tsuchiya TEL:（089）927-8198
E-mail takut@sci.ehime-u.ac.jp
