High-pressure, synthetic loveringite-davidite and its rare earth element geochemistry

Loveringite-davidite members of the crichtonite group were synthesized at high pressure and temperature (7.5 kbar, 1000-1050 ~ from a melt of TiO2 and rare earth element (REE) enriched basaltic andesite composition. Four sets of partition coefficients for La, Sin, Ho, Lu and Sr (analogue for Eu 2+) were obtained. These show that light and heavy REE are readily accommodated, but the intermediate REE are discriminated against in the loveringite-davidite structure. This confirms the previously proposed two sites (A and M) for REE substitution in the crichtonite group. Additional experiments verified the stability of REE-rich crichtonite group minerals to 20 kbar, 1300 ~ and 30 kbar, 1000 ~ and indicate that this phase may be an important accessory repository for the light and heavy REE in the upper mantle.