AN IN-SITU X-RAY-DIFFRACTION STUDY OF THE ALPHA-BETA TRANSFORMATION KINETICS OF MG2SIO4

This is the first report of the direct measurement of alpha-beta trans formation kinetics in Mg2SiO4, a major constituent in the Earth's mant le, through in situ X ray diffraction experiments at high pressure. Th e experiments were conducted using the sintered diamond cubic-anvil ap paratus with synchrotron radiation (MAX 80). Although the present work is still preliminary, the kinetic data were analyzed using a nucleati on and growth model. The growth rate of beta-phase is determined to be 3.3 (1.6 similar to 4.9) x 10(-10) m/s at 13.0 GPa and 900 degrees C, 7.1 (3.4 similar to 10) x 10(-10) m/s at 14.1 GPa and 885 degrees C, and 1.5 (0.7 similar to 2.3) x 10(-9) m/s at 14.9 GPa and 875 degrees C.