Post-garnet high-pressure transition; effect of heterogeneous laser heating and introduction of some new techniques

The post-garnet high-P transition has been studied at >><$I> 25 GPa, and recovered samples characterized by SEM, TEM, EPMA and XRD. It is clear that in the case of garnet the resultant high-P phases differ considerably depending on the details of the high-P experiments. Heterogeneous heating by YAG laser in the diamond-anvil cell may be responsible for some of the complexity of previous results. Much more uniform heating of the sample is possible using a resistance furnace in a Drickamer-type apparatus or CO (sub 2) -laser heating in a diamond-anvil cell. Current experiments indicate that end-member pyrope transforms into a mixture of perocskite and corundum phases in the P range of approximately 30 GPa.