The specific features of eclogitic paragenesis of diamonds from Mir and Udachnaya kimberlite pipes (Yakutia)

The paper summarizes both published and unpublished compositional data of g arnets and pyroxenes from eclogitic type (E-type) paragenesis diamonds from Mir and Udachnaya kimberlite pipes (Yakutia). The database includes about 50 xenoliths of diamondiferous eclogites from the Mir pipe, more than 150 s imilar xenoliths from the Udachnaya pipe, and up to 100 E-type diamonds wit h inclusions from both pipes. Garnets and pyroxenes from seven new samples of diamondiferous eclogites (three from Mir and four from Udachnaya) are an alyzed as well as from four E-type diamonds from the Udachnaya pipe. Two of the diamonds contain abundant garnet and pyroxene inclusions (40 - from Ud -4/90 and 17 - from Ud-10/90). Two other diamonds (Ud = 11/90 and Ud - 20/8 6) contain coesite inclusions in addition to garnet and pyroxene. Most of t he inclusions have imposed octahedral morphologies. Garnets from diamondife rous eclogites form a continuous series of compositions, for both Mg# and C a#, with most calcic garnets present in kyanite-bearing assemblages. Garnet s from Mir eclogites are sometimes zoned and have lower Mg# compared with t hose from Udachnaya, where about 50 % eclogite garnets possess Mg# 65 and m ore. All E-type garnets from Mir diamonds and eclogites plot within the fie ld of garnet compositions related to diamonds worldwide. In contrast, E-typ e Udachnaya garnets, especially from diamondiferous eclogites, occupy a muc h wider compositional field, expanding to higher Mg# side (about 30 % of al l samples), along with wide variations in Ca#, from 10 to 55 %. Pyroxenes f rom diamondiferous eclogites from both locations contain more Na2O and cons iderably less K2O when compared to diamond inclusion pyroxenes. This is als o confirmed by a study of 10 samples of diamondiferous eclogites containing diamonds with inclusions. Complex and variable of garnet and pyroxene comp ositions are typical of diamonds from both pipes containing multiple inclus ions. Based upon garnet and pyroxene compositions it is concluded that Grou p A diamondiferous E-type assemblages are virtually absent from the Mir pip e and represent about 20 % of all samples from Udachnaya. The wide range of garnet-pyroxene compositions in multiple-inclusion diamonds, as well as be tween diamond inclusions and minerals of the same host eclogite, reflect th e complex growth history of eclogitic diamonds and their hosts, and partici pation of mantle metasomatic fluids in their formation.