P- and S-wave velocities (VP and VS) are the unique tool we have to explore the inaccessible deep Earth via comparisons with the observed seismic
velocities. In this FY we measured VP and VS of Harzburgite (Hz), which constitute the main body of the subducted lithosphere. The Hz samples were synthesized at high Pressure and Temperature at GRC (Ehime University), starting from a glass of Hz composition fabricated in a laser levitation furnace at IPGP (Paris University)
The sound velocities of the Hz aggregates were determined by in
situ ultrasonic interferometry, X-ray radiography and diffraction techniques, at high P and T in the multianvil press at the beamline Bl04B1 located at the synchrotron facility SPring-8. The analyzed samples consisted of majorite, akimotoite and olivine at P ~20 GPa and bridgmanite and periclase at P> 25 GPa, accordingto the synthesis Pressure. An additional experiment on Mid-Ocean Ridge Basalts (MORB) at P ~25 GPa was also conducted to support the results of the previous FY. Preliminary results indicated the VS/VP of Hz are higher than those of seismic models across the 660-km depth discontinuity, suggesting harzburgitic fragments could explain the high shear seismic velocities observed above the 660, while slower materials, such as MORB or partial melt are necessary to explain the low velocities beneath the 660.
