Exhumation and tilting of the western metamorphic belt of the Coast orogen in southern southeastern Alaska

The uplift history of the western metamorphic belt in southern southeastern Alaska can be traced using emplacement depths and cooling ages of mid‐Cretaceous plutons which intruded the metamorphic belt during the period 101 Ma to 89 Ma. During the period 101 Ma to 94 Ma the rocks of the metamorphic belt now at the surface were buried to a depth of approximately 30 km. Pressure data indicate that by 89 Ma the western portion of the metamorphic belt was at a shallower crustal level (∼23 km within the study area) while the eastern side remained at a depth of approximately 30 km. Cooling curves constructed from minerals in mid‐Cretaceous plutonic rocks indicate that the western side of the metamorphic belt cooled earlier than the eastern side; an observation consistent with the inferred uplift history. Southwestward transport of metamorphic belt rocks within the hanging walls of thrust and high‐angle faults may have provided one mechanism for uplift during mid‐ to late‐Cretaceous time. The eastern portion of the western metamorphic belt cooled rapidly at ∼55 Ma, probably in response to a period of rapid uplift. The Coast shear zone, an Early Tertiary high‐angle fault with west‐side‐up displacement, bounds the east side of the metamorphic belt. We suggest Tertiary uplift occurred by tilting of the metamorphic belt due to movement along this fault.