Mantle xenoliths from the Attawapiskat kimberlite field, James Bay Lowlands, Ontario

A chemical investigation of coarse textured, garnet-bearing peridotite xenoliths and xenocrysts from the Attawapiskat kimberlite field was undertaken. The kimberlites occur in the James Bay Lowlands, in the Sachigo subprovince of the Superior Craton.; Fragments of coarse textured lherzolite, harzburgite and eclogite occur as microxenoliths (≤1.5 cm diameter). Most of the xenoliths occur as one or two phase assemblages (olivine ± orthopyroxene, clinopyroxene, garnet, spinel). Garnet-bearing assemblages were investigated for the purposes of geothermobarometry.; Calculated pressures and temperatures of equilibration indicate that garnet harzburgites equilibrated at depths within the diamond stability field, and garnet lherzolites at depths within the graphite stability field. All the xenoliths equilibrated near a 40mWm–2 subcratonic steady-state geothermal gradient.; Extensive modal metasomatism occurred in the mantle prior to xenoliths being incorporated into the kimberlite magma. This metasomatism extended to great depths below the Superior Craton in the Attawapiskat region.