DEEP-CRUSTAL AND LOCAL RHEOLOGICAL CONTROLS ON THE SITING AND REACTIVATION OF FAULT AND SHEAR ZONES, NORTHEASTERN NEWFOUNDLAND

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 th e trace of a fundamental contact between two Gondwanan basement blocks displaced sinistrally relative to one another during Silurian orogene sis. Changes in plate motion during the Devonian led to kinematic reve rsal 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 defor mation and shifts in siting of shear were closely related to magma pre sence. We consider that granite magmas exploited shear zones within th e crust to aid ascent, and in doing so enhanced local deformation. Ces sation 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 control led by regional-scale pre-existing basement configuration and more loc alised processes affecting rheology, notably plutonism.