Significance of eclogitic and related parageneses of natural diamonds

Eclogitic (E-type) and related parageneses of natural diamonds are represen ted by suites of dia mend inclusions and xenoliths of diamondiferous eclogi tes. Major-element data are presented for 32 coexisting minerals forming 19 bimineralic and trimineralic inclusions from diamonds, including omphacite -orthopyroxene (1 sample), garnet-omphacite (5 samples), garnet-coesite (5 samples), omphacite-coesite (2 samples), garnet-picroilmenite (2 samples), garnet-kyanite (1 sample), omphacite-phlogopite (2 samples), and garnet-omp hacite-phlogopite (1 sample). Major-element variations of coexisting minera ls are typical of corresponding eclogites. Omphacite with 5.02 wt% Na2O, in tergrown with orthopyroxene with Mg#83.7, represents the first example of a diamondiferous websterite paragenesis including Na-clinopyroxene. This ind icates a broader range in mineral compositions of E-type-related websterite -pyroxenite-associated diamonds than known previously. This unique websteri te-pyroxenitic mineral assemblage represents a transitional paragenesis bet ween peridotitic or ultramafic (U-type) and E-type parageneses. Bimineralic eclogites, ilmenite eclogites, coesite + corundum + kyanite ecl ogites, and grospydites occur not only as sets of inclusions in diamonds bu t, with a few exceptions (ilmenite and coesite eclogites), also as diamondi ferous eclogite xenoliths. The coesite eclogite paragenesis is a significan t inclusion suite in diamonds, and was detected in about 15 diamond occurre nces worldwide. It represents from 15% to 22% of all E-type diamonds in sev eral occurrences, and thus should not be considered as rare.