Phase changes and rheological properties of Earth and planetary materials under high-pressure and high-temperature

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Phase relations, structures and physical properties, phase transformations and rheological properties of important Earth and planetary materials under high-pressure and high-temperature were clarified in these 2 years from 1998 to 2000. In each year, a meeting was held to present and discuss the results of the above subjects, and communicate with each other. The clarified results are as follows;1) In the garnet-perovskite transformation, Al in silicate perovskite increases with pressure and temperature, and a new high-pressure aluminous silicate phase was found (Fujino).2) The crystal structure of a new hexagonal phase in MgAl2O4-CaAl2O4 was determined (Fujino).3) Natural silicate ilmenite and perovskite were discovered in a shocked meteorite, and their formation mechanism was clarified (Fujino).4) A new high-pressure phase was found and its stability field was determined in MgAl2O4-CaAl2O4 (Akaogi).5) The phase boundary between spinel and perovskite+periclase in Mg2SiO4 was determined by the high-pressure and high-temperature in situ X-ray observation (Irifune).6) In the high-pressure experiments of the basalt and peridotite compositions up to 27 GPa, K changed to a compatible element under the transition-zone and lower mantle conditions (Takahashi).7) Kinetics of the alpha-beta transition and the decomposition of the gamma phase in Mg2SiO4 were clarified by the in situ X-ray observations and electron diffraction studies (Ohtani).8) The crystal structure of alpha-CaSi2O5 synthesized at 1500 C, 10 GPa was determined, and 5-coordinated Si was found (Kudoh).9) Crystal structures and physical properties of Mg2SiO4 polymorphs could be reproduced in high precision by the molecular dynamics simulation (Matsui).10) A time-resolved new system to analyze phase transitions was developed using a diamond anvil cell with a heater (Yamanaka).11) A basic equation to describe the composition of a growing solid solution crystal could be derived (Kitamura).