EXTREME CHEMICAL DIVERSITY IN THE MANTLE DURING ECLOGITIC DIAMOND FORMATION - EVIDENCE FROM 35 GARNET AND 5 PYROXENE INCLUSIONS IN A SINGLEDIAMOND

We report major- and trace-element variations in 35 garnet inclusions extracted from a single eclogitic diamond from the Mir kimberlite pipe , Yakutia. The range in CaO and Mg# in these garnets is large-from 3.8 4 to 9.66 wt% and 45 to 56, respectively. These ranges cover nearly ha lf of the total range in eclogitic garnet compositions from diamonds w orldwide. An extremely wide range in trace elements such as Y, Zr, aci d Sr also covers nearly the total range recorded for garnets included in diamonds, as well as that known for rock-forming minerals of diamon diferous eclogite xenoliths-15.1 to 48.9 ppm Y; 2.2 to 40.8 ppm Zr; an d 0.5 to 9.1 ppm Sr. The widest ranges in REE between different grains (by an order of magnitude) are noted for LREE and MREE. Such composit ional ranges are the first recorded for garnets available as inclusion s in a single eclogitic diamond and cover nearly the complete range of compositions known for all Yakutian eclogites. Five clinopyroxene inc lusions exhibit more moderate ranges in both major- and trace-element abundances. Na2O compositions vary from 5.1 to 5.7 wt% and Mg# varies from 72 to 76. Trace-element abundances analyzed from two clinopyroxen e inclusions are rather similar to those in eclogite xenoliths from Mi r, but REE patterns span the range from LREE-depleted to LREE-enriched . These observations reflect the complex growth history of eclogite di amonds and their xenolith hosts, as well as the extreme chemical diver sity in the mantle environment during their growth. The variability in garnet composition is attributed to changing fluid chemistry in succe ssive metasomatic fronts moving through a subducted oceanic slab in th e mantle. These metasomatic fluids also could have been the carbon sou rce for the diamond.