Post-Caledonian tectonics along the Billefjorden fault zone, Svalbard, and implications for the Arctic region

Abstract

The north-south Billefjorden fault zone of northern Spitsbergen in the Svalbard archipelago has been widely regarded as one of the classic areas for transpressional tectonics. The fault zone coincides with a late Caledonian shear zone and presently constitutes the eastern boundary of the main Devonian basin of northern Svalbard. Fold axial traces and thrust faults that developed in the Devonian to Permo-Carboniferous rocks parallel the strike of the fault zone. There is no evidence for the rotation of fold hinges, and nonaxial planar, transecting cleavages are lacking. Folds and thrusts with similar geometries affect the whole 60-km-wide Devonian basin fill. These observations, together with analyses of fault and fold patterns, indicate (A) pre-Devonian (Caledonian) left-lateral ductile shearing; (B) Late Silurian-Early Devonian extension; (C) Late Devonian-early Carboniferous inversion accompanied by folding of Devonian sedimentary rocks; (D) early Carboniferous extension followed by platform-wide subsidence into late Mesozoic time; (E) Late Cretaceous-Paleocene, east-west contraction, thrusting, and folding; and (E) post-Paleocene east-west extension. The Late Devonian deformation along the Billefjorden fault zone is compared with the Late Devonian to early Carboniferous Ellesmerian orogeny of the Canadian Arctic. The Late Devonian megashear model for the tectonic evolution of the North Atlantic region is not supported by the evidence from Svalbard.