Eclogites from the Obnazhennaya Kimberlite Pipe, Yakutia, Russia

Mineralogy and petrography of six eelogite xenoliths from the Obnazhennaya kimberlite pipe ar e described. Based upon modal and mineral compositions, these eclogites can be divided into Group A (five samples) and Group B (one sample), as per Coleman et al. (1965) and Shervais et al. (1988). Group-A eclogites are orthopyroxene-bearing, and their constituent minerals have high Mg# and Cr2O3 content. The clinopyroxenes in this type of eelogite have low jadeite component. The geochemical features of Group-A eclogites are similar to garnet pyroxenite, and e believed to be the product of high-pressure fractionates from an alkaline basaltic melt in thear upper mantle. Group-B eelogite (0-82/91) contains higher Al2O3 and FeO and lower MgO and Cr2O3; its composition is similar to a high-aluminum basalt or gabbro. This eelogite could have crystallized under high pressure in the upper mantle from a basaltic melt, without significant fractionation. Alternatively, it also could be the relict of subducted oceanic crust...