550 SHORT COMMUNICATIONS

recently argued on experimental grounds that the olivine Kd is pressure-dependent. Whereas there are no comparable experimental data for the opx/ liquid Kd relationship, available data (for example, Frey and Prinz, 1978) suggest that the Kd relation-ships vary sympathetically in these two mineral groups. Therefore, both olivine and orthopyroxene would be expected to become more Mg-rich with reduced pressure. We envisage that the orthopyro-xene phenocrysts grew Mg-rich cores zoned to relatively Fe-rich rims at depth, were abruptly transported to a much lower pressure (sub-volcanic?) regime, then developed Mg-rich over-growths which again became zoned to relatively Fe-rich rims. Thus a double-rim is developed in these phenocrysts. Acknowledoements. Laboratory and field expenses for thi