Perovskite-bearing crystal-controlled oxide-silicate mantle xenoliths: Resolution to controversial origins?

Abstract

Classic lamellar clinopyroxene-ilmenite intergrowths (type 1) are extended to include discovery of olivine-ilmenite-perovskite-wüstite (type 2) and olivine-spinel-perovskite (type 3) xenoliths in kimberlites from Liberia. Low titanium solubilities in olivine, garnet, and pyroxene cannot account for exsolution-like relations. Because the oxides coexist with high-pressure perovskite-structured silicate minerals in diamond, a permissive conclusion is that type 1 to type 3 xenoliths are of super-deep origin. Phase equilibria and thermodynamic studies show that type 1 xenoliths are stable at P > 80 GPa, with type 2 and type 3 at 35 to 50 GPa consistent with an origin in anomalous large low shear velocity province bodies anchored at the core-mantle boundary. Dissociated precursor perovskite-structured Ca-Fe-Ti bridgmanite is proposed and is indirectly supported by the copresence of type II diamonds with a sublithospheric lower mantle origin.