Trace elements in minerals of eclogites from Udachnaya kimberlite pipe (Yakutia)

Results of investigation of trace element abundance in rock-forming garnet and clinopyroxene as well as oxide and sulfide minerals of eclogite xenoliths from Udachnaya kimberlite pipe are presented. Investigated samples have been chosen from different varieties of xenoliths, including diamondiferous ones. Trace element analyses have been undertaken on the HIAF proton microprobe at the CSIRO in Sydney, Australia. The analyzed garnets show a wide range in Ni (10-140 ppm) and large range in both Y and Zr. Garnets of kyanite eclogites are depleted in both Y and Zr and in some specimens enriched in Sr. The garnets from eclogite xenoliths of Udachnaya pipe show similar trace element concentrations to those from eclogites of South Africa and garnet inclusions from Monastery and Argyle, but in detail, they range to lower Ni values and are depleted in Y and Zr. In all groups of xenoliths clinopyroxenes show a wide range in Ni (45-560 ppm) and poor correlation with Mg#. The pyroxenes from diamondiferous eclogites are depleted in Zn (22-75 ppm) and Ga (10-27 ppm) and enriched in Zr (4-40 ppm) relative to the minerals from other xenoliths. Clinopyroxenes from kyanite eclogites show a considerably larger range in Ga (16-35 ppm) and Sr (190-470 ppm) concentrations than those from bimineralic eclogites. In comparison with clinopyroxenes from eclogites of South Africa and those of inclusions in diamonds of eclogitic paragenesis from Monastery and Argyle they range to higher Sr values and are slightly depleted in Y and Zr and enriched in Ga. Sulfides from eclogite xenoliths are high in Mo, Zn, Ag, Ru and Pd compared to the sulfides of the peridotite suite. A high content of Mo and sometimes Se in pyrrotites is typical of most part of sulfides from diamondiferous xenoliths. The djerfisherites are strongly enriched in Zn, As, Ag, Pb, Rb and sometimes in Sr, confirming their relation to metasomatic and/or partial melting processes. Rutiles have very high Zr contents (0.12-0.65%) and are enriched in Zn. Zr/Hf varies considerably and usually is >25. It is proposed that enrichment or depletion of garnet and clinopyroxene and probably other minerals in some trace elements is due to a complicated metasomatic evolution after their formation and subsequent or simultaneous partial melting of eclogite material in the mantle.