Structural evolution of a transpression zone in north central Newfoundland

Abstract

A dextral transpression zone in Notre Dame Bay, north central Newfoundland, was active in Middle to late Silurian times following the closure of a marginal basin. The deformation in the transpression zone was complex and involved several generations of structures. Deformation was initially distributed over wide, low-strain zones through the formation of a penetrative regional cleavage. With steepening and overturning of the strata, the orientation of the sequence was favorable for strike-slip bedding-parallel movement and the deformation became more efficiently accommodated by shear within the incompetent lithologic horizons, forming localized shear zones in high-strain zones. The sheared incompetent horizons define a belt of mélange, the ‘Boones Point Complex’, centered on the contact between a volcanic island arc terrane to the north and a marginal basin terrane to the south. Two cleavages with similar orientation and morphology were generated at different times during the structural evolution of the transpression zone. One of the cleavages is regional in distribution, and is transposed by the shear zones. Folds with no axial-planar cleavage, but a cleavage cutting obliquely across their hinges, are reported. They have the geometry of transected folds but are clearly the result of overprinting by a younger generation of cleavage.