High Pressure Mineral Reactions in a Pyroxenite Granulite Nodule from the Stockdale Kimberlite, Riley County, Kansas

Abstract

Sapphirine, kyanite, and a grossular-rich garnet have formed by reactions involving spinel, pyrope-almandine, clino- and orthopyroxene, and plagioclase in a pyroxenite granulite nodule from the Stockdale kimberlite, Kansas. The reactions responsible for formation of these minerals are thought to have occurred at pressures in excess of 13.5 kilobars (corresponding to a depth of formation of approximately 40 km) thus placing the source material for the nodule in the upper mantle. Sapphirine and kyanite are reported for the first time from the Riley County, Kansas, kimberlites.