Abstract

The siting of a c. 25 km wide, transpressive, high-strain zone at the eastern margin of the Gander Zone of NE Newfoundland corresponds to the trace of a fundamental contact between two Gondwanan basement blocks displaced sinistrally relative to one another during Silurian orogenesis. Changes in plate motion during the Devonian led to kinematic reversal and reactivation of the shear zone and, at high structural levels, the development of a major brittle-ductile fault system. At a local scale within the Silurian ductile high-strain zone, the focus of deformation and shifts in siting of shear were closely related to magma presence. We consider that granite magmas exploited shear zones within the crust to aid ascent, and in doing so enhanced local deformation. Cessation of magma supply and/or cooling of magmas within conduits caused deformation to relocate elsewhere. NE Newfoundland hence provides an example of how fault/shear zone siting and reactivation may be controlled by regional-scale pre-existing basement configuration and more localised processes affecting rheology, notably plutonism.

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