DISTRIBUTION OF TRACE-ELEMENTS BETWEEN AMPHIBOLE AND CLINOPYROXENE FROM MANTLE PERIDOTITES OF THE EIFEL (WESTERN GERMANY) - AN ION-MICROPROBE STUDY

The pargasite/diopside partition coefficients (D) for the rare-earth e lements (REE), Sr, Y, Zr and I-If determined with ion-microprobe analy sis on low-temperature West Eifel mantle peridotites, have values of b etween 1 and 2. In contrast, Nb and Ba are strongly enriched in amphib ole with partition coefficients of D-Nb=100-200 and D-Ba>1000. Small s ample-to-sample variations in the REE partition coefficients in the We st Eifel samples appear to be related to compositional factors, specif ically the Na content of clinopyroxene. The REE partition coefficients of edenitic-pargasitic hornblende/diopside pairs from East Eifel xeno liths have higher values (D=3-8) than those from the West Eifel and th ese differences may be attributable to the lower Na and K contents of the East Eifel xenoliths. The partition coefficients for amphibole/cli nopyroxene pairs of natural peridotites differ from the literature val ues for those of high-temperature melts. Compared to the West Eifel xe noliths most of the melt-related partition coefficients are higher for LREE (D=2-4), but decrease and become similar for HREE (D=1). It is u nclear to what extent these differences are the result of temperature, pressure and composition, or the result of lack of equilibrium.