Oxygen isotope geothermometry and stability of lawsonite and pumpellyite in the Shuksan Suite, North Cascades, Washington

Metamorphic temperatures of 330??-400?? C are inferred for rocks from the Shuksan blueschist terrane in the North Cascades, Washington. The temperatures are calculated from 18O fractionations between coexisting quartz and magnetite using the equations of Bottinga and Javoy (1973). Pressures of approximately 7 kilobars are indicated by the Jadeite content of clinopyroxene coexisting with quartz+albite. Published experimental and theoretical studies of the stability of lawsonite and pumpellyite are consistent with the oxygen isotope temperatures and occurrence of these minerals in the Shuksan Suite. ?? 1982 Springer-Verlag.