Deformed and metamorphosed rock assemblages recognized in the Bay of Islands ophiolite complex.

Deformation and metamorphism occur in several geological settings within this complex in W Newfoundland. At least five metamorphic assemblages are distinguished on the basis of: 1) relative age determined by cross-cutting field relationships; 2) style of recrystallization relative to deformation; 3) assemblage of metamorphic facies present; 4) protolith(s); and 5) distribution of metamorphic rocks and implied thermal gradients with respect to the ophiolite structure. The five assemblages are related to: 1) high-T, solid-state, anhydrous deformation of residual upper mantle and some cumulate rocks during mantle upwelling and spreading; 2) static hydrothermal metamorphism and extensional tectonics in the upper crustal units during sea-floor spreading; 3) asymmetrical deformation and metamorphism across a steeply-dipping shear zone that transects the ophiolite allochthon and which was produced by transform faulting; 4) low-angle ductile shearing and metamorphism forming a basal metamorphic aureole during obduction of the ophiolite; and 5) late static serpentinization of the ultramafic units after obduction and transportation.-C.N.