Polyphase metamorphic evolution of a Late Triassic subduction complex, Klamath Mountains, northern California

The Stuart Fork terrane in the central Klamath Mountains of northern California is a Late Triassic subduction complex which documents early plate convergence in western North America. Mineral fabrics, assemblages, and compositions in Stuart Fork terrane metasedimentary and metavolcanic rocks reflect three distinct periods of recrystallization: M₁, a greenschist-facies hydrothermal metamorphism observed only in metabasalts; M₂, a widespread blueschist-facies metamorphism; and M₃, a greenschist- to amphibolite-facies contact metamorphism. The Stuart Fork is composed of a coherent blueschist belt of greater extent than previously accepted, and its polyphase metamorphic evolution records more than 80 Ma of continuous, east-directed convergence along the latest Paleozoic and early Mesozoic western North American continental margin. -from Author