Composition of the Lithospheric Mantle in the Siberian Craton: New Constraints from Fresh Peridotites in the Udachnaya-East Kimberlite

Abstract

We present petrographic, major element and trace element data for bulk-rocks and minerals for a suite of 34 remarkably fresh peridotite xenoliths in the Udachnaya kimberlite recovered from deep horizons of the open pit mine. The xenoliths are spinel peridotites, granular and deformed garnet peridotites (as well as a megacrystalline dunite) in proportions similar to those reported by previous work on altered xenoliths from less deep levels in the mine. Equilibration tem-peratures (T) range from 760^9658C for the spinel peridotites to 1200^13208C for sheared garnet peridotites; the latter yield pres-sures (P) of 5·4^6·6 GPa.The majority of the granular garnet peri-dotites equilibrated at 860^10008C and 2·6^5·5 GPa, but two samples yield much higher T and P values (11768C, 6·1GPa; 13408C, 6·8 GPa) indicating the presence of undeformed rocks near the base of the lithosphere. Strong enrichments in silica and opx rela-tive to dry melting residues are not common in our granular perido-