Single crystals of olivine, forsterite, and enstatite were heated to over 2000 K between 100 and 250 kbar with a 120 W CO2-laser in a diamond anvil cell using a hydrostatic, inert gas pressure medium. The conversion to some of their high pressure polymorphs, &bgr;-phase, &ggr;-phase, perovskite, majorite, ilmenite, and clinoenstatite yielded single crystal large enough to obtain high quality Raman spectra, thus providing a quick, economic, precise method to measure phase diagrams without pressure quenching.

The phase boundaries between olivine of forsterite and &bgr;-phase and between &ggr;-phase and perovskite were accurately bracketed. Our preliminary results on the latter transition are within the P--T uncertainties of the previous measurements using multi-anvil devices [Ito and Takahashi, 1989>, constraining the temperature at 670 km depth to 1900¿100 K, which is about 300 K higher than using their best estimate of the phase boundary.

The unquenchable phase of MgSiO3-clinopyroxene was synthesized at ~170 kbar; Raman spectra show that this phase is of C2/c symmetry. Its stability field is between 50 and ~165 kbar at ambient temperature.

MgSiO3 perovskite was synthesized above 230 kbar and ~2000 K. Raman spectra were measured from 75 to 470 kbar. Above 370 kbar, two modes disappear and two other change slope with pressure, suggesting a change in symmetry from Pbnm at room temperature. ¿American Geophysical Union 1991