K-Ar illite and apatite fission track constraints on brittle faulting and the evolution of the northern Norwegian passive margin

- New K-Ar illite and AFT ages from onshore northern Norway
- Timing of post-Caledonian brittle extensional faulting and exhumation
- Widespread Permian brittle faulting event onshore and offshore
- The location of the extensional deformation migrated southwestward post-Permian.

Determining the timing of post-Caledonian brittle faulting in northern Norway is important for the understanding of the extensional tectonic evolution of the north Norwegian continental margin. Fault gouges from the Troms and Vesterålen regions of northern Norway yield Carboniferous to Permian and Carboniferous to Cretaceous K-Ar illite ages, respectively. The results show a contrast in fault activity and exhumation between the Troms and the Vesterålen regions: while major faulting in the Troms region appears to have ceased after the Permian faulting event, faulting continued into at least the Cretaceous in the Vesterålen region. The findings highlight the importance of a widespread Permian tectonic event followed by a distinct southwestward migration of post-Permian tectonic activity on the north Norwegian passive margin. Late Triassic to Early Jurassic apatite fission track ages do not show significant age offsets across major fault zones in Troms, indicating that most or all of fault activity took place prior to the Late Triassic. The thermal history models are consistent and indicate continuous cooling to about 60 °C in the Late Permian-Triassic.