Structural evolution and tectonic significance of the Eastern Highlands shear zone in Cape Breton Island, the Canadian Appalachians

Abstract

The Eastern Highlands shear zone in Cape Breton Island of the Canadian Appalachians is characterized by an amphibolite-facies deformation zone over 5 km wide overprinted by a greenschist-facies mylonite zone about 1 km wide. Deformation zones in both metamorphic grades dip steeply to the southeast with movement direction pitching steeply to the southwest, and shear sense indicators indicate the same sense of shear, that is, an east-over-west dip-slip movement with minor sinistral strike-slip component. Deformation in both conditions is constrained to the Late Silurian to Early Devonian (mainly Late Silurian). It is suggested that the greenschist-facies deformation represents the last stage of a single episode of deformation that occurred initially under amphibolite-facies conditions. The west-vergent shearing along the shear zone is antithetic to the westward subduction that led to the Silurian continent-continent collision, which is interpreted by tectonic wedging in this part of the Canadian Appalachians.