Coherent French Range blueschist: Subduction to exhumation in <2.5 m.y.?
Coherent oceanic strata in the French Range belong to the exotic Cache Creek terrane of the Canadian Cordillera. They were metamorphosed to blueschist grade, tectonically extruded, eroded, and intruded by plutons—perhaps in <2.5 m.y. Sodic amphibole overprint chert as young as late Pliensbachian to Toarcian age (ca. 191 to ca. 177 Ma). Blueschist mineral assemblages defi ne the early metamorphic fabric along with phengite dated by 40 Ar/ 39 Ar as 173.7