Orogenic peridotites from the Seventymile Terrane of Eastern Alaska and the Atlin Terrane of Northern British Columbia are compositionally different. The peridotites from Alaska are enriched in light rare earth elements and the mineral chemistry indicates that they were oxidizing. The peridotites from British Columbia are depleted in light rare earth elements and the mineral chemistry indicates that they were reducing. It is likely that the compositional and redox differences between the peridotites is related to their tectonic setting. The Alaska rocks represent enriched oceanic lithosphere from an active margin whereas those from British Columbia are representative of a suprasubduction zone.