EXPERIMENTAL-DETERMINATION OF PARTITION-COEFFICIENTS FOR RARE-EARTH AND HIGH-FIELD-STRENGTH ELEMENTS BETWEEN CLINOPYROXENE, GARNET, AND BASALTIC MELT AT HIGH-PRESSURES

Clinopyroxene/melt and garnet/melt partition coefficients have been de termined for Ti, Sr, Y, Zr, Nb, Hf, and rare earth elements from 19 do ped experiments on 1921 Kilauea basalt. The experiments were carried o ut from 2.0 to 3.0 GPa and 1310 degrees to 1470 degrees C. The purpose was to derive a set of partition coefficients for high-held-strength elements (HFSE) and rare earth elements (REE) in a systematic, linked set of experiments at P and T conditions relevant to basalt petrogenes is. These data are used in melting models to understand the developmen t of negative HFSE anomalies observed in many abyssal peridotite clino pyroxenes. It is shown that melting can account for the observed trace element patterns in some residual peridotites, but that other process es may also be needed to account for most residual mantle compositions in mid-ocean ridge systems. It is also shown that REE are more strong ly fractionated by garnet at these P-T conditions than previously thou ght.