Structural analysis and measured extension in fault complexes along the Lofoten-Vesterålen margin, offshore Norway, in the context of crustal-scale rifting towards breakup in NE Atlantic

Abstract

Abstract Late Cretaceous–Palaeocene continental extension within the Lofoten‐Vesterålen margin is investigated by integrating 2D‐3D seismic and potential field datasets, together with updated crustal transects. Most of that deformation is recorded by two low‐angle detachment structures named West Røst High Fault Complex (WRHFC) and North Utrøst Ridge Fault Complex (NURFC) located at the southern and central‐northern portions of the studied area, respectively. Multiple extensional episodes of various intensities were mapped as different fault stages, including one Albian‐Cenomanian phase, four early Late Cretaceous phases, three Late Cretaceous to latest Cretaceous–Palaeocene phases, and one Palaeocene phase. The WRHFC is narrower in extent and has accommodated a relatively greater amount of localized extension (ca. 18–19 km), whereas the NURFC occupies a wider area with widespread extension intensity (ca. 6–8 km). In comparison, the total across‐margin average extension within the southern, central, and northern portions of the Lofoten‐Vesterålen and NE Greenland conjugate margins are ca. 192, 221, and 266 km, respectively. Such results indicate an apparent extension discrepancy between derived extension from measured fault‐block geometries within the fault complexes and the whole conjugate margin system, with only ca. 11% and 13% of the extension seen on the studied seismic profiles on the WRHFC and NURFC, respectively. The corrected maximum extension for purely sub‐seismic resolution faulting on both the WRHFC and NURFC fault complexes is ca. 164 and 46 km, respectively. Finally, both WRHFC and NURFC structures provide key evidence for a ductile mode of deformation towards breakup that is expressed through shear zones‐rift topography interactions with overlaying listric/detachment faults. These features reflect the resulting multiphase tectonic evolution across the asymmetric Lofoten‐Vesterålen and NE Greenland conjugate margins, and the obliquity in the breakup axis location along them. The study outcomes are pertinent and applicable to understand the breakup evolution of the northern NE Atlantic and its vicinity.