Microstructure, metamorphism and tectonics of the western Cape Breton Highlands, Nova Scotia

Abstract

ABSTRACT Microstructural and petrological data from the Jumping Brook metamorphic suite, western Cape Breton Highlands, suggest that a single episode of syntectonic prograde metamorphism, followed by uplift, cooling and associated retrogression, affected these rocks during mid‐Palaeozoic times. Microstructures indicative of progressive crenulation foliation development can be traced from low‐grade (chlorite zone) through high‐grade (kyanite zone) rocks, allowing a clear sequence of porphyroblast growth to be established. Metamorphic reactions and P‐T calculations suggest metamorphic conditions of 700‐750°C at 8‐10 kbar were achieved in kyanite zone rocks. Although a complete P‐T‐t path was not defined, combined petrological and geochronological data can be used to constrain computed P‐T‐t models. These models suggest that a component of post‐metamorphic tectonic exhumation is required to explain the observed times of cooling and uplift. The microstructural and petrological data to not support the interpretation that the high‐grade rocks represent pre‐existing crystalline basement. Indeed, the metamorphic history, geochronology and computed tectonic models all point to a single, short‐lived episode of Silurian‐Devonian volcanism, intrusion, convergence, regional metamorphism and uplift, probably resulting from collision tectonics at an irregular continental margin.