Abstract
In Scandinavia, the 1.15-0.90 Ga Sveconorwegian orogen is transected by major N-S trending shear zones separating lithotectonic segments. East of the Oslo Rift, the Idefjorden terrane hosts lithologically distinct, but spatially related post-compressional intrusions emplaced along similar WNW trends. The Vinga intrusion yields a 963±17 Ma age, which combined with other U-Pb results from this terrane, permits recognition of discrete post-compressional igneous episodes at 1041-1030, 984, 963, and 920 Ma. After final Sveconorwegian convergence and accompanying metamorphism by 969 Ma, gravitational collapse and related extension allowed ascent of the Vinga magma into a WNW fracture. We note that extensional movements with a sinistral strike-slip component confined to the N-S trending shear zones that bound the Idefjorden terrane, provide an emplacement mechanism for post-compressional magmas into the resulting WNW-trending fracture system.
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