Supradetachment basins in necking domains of rifted margins: Insights from the Norwegian Sea

Supradetachment basins at passive rifted margins are a key witness of major-continental extension, and they may preserve a record from which the amount and rates of extension and metamorphic core complex exhumation may be reconstructed. These basins have mainly been recognised in back-arc and orogenic collapse settings, with few examples from rifted margins. Using 2D and 3D seismic reflection, wellbore, and gravity anomaly data, we here characterise the three-dimensional structural and tectonosedimentary evolution of a spoon-shaped supradetachment basin that was formed in the necking domain of a rifted margin, at the southern limit of the More and Voring segments of the Norwegian rifted margin. The basin, with an areal extent of ca. 2400 km(2), and a landward-rotated syn-tectonic succession up to ca. 30 km thick (true stratigraphic thickness), is separated from footwall continental margin core complex basement culminations by major large-offset (>30 km) normal fault complexes characterised by a cross-sectional geometry whereby an upper, steeper part of the fault gives way to a low-angle detachment fault at depth. These fault complexes are associated with a tectonic thinning of the continental crust to ca. 11 km, compared with a crustal thickness of ca. 27 km in the proximal domain. The basin is filled by a succession of pre-, syn- and post-tectonic deposits, that accumulated over time as the basin evolved over a series of rift- and detachment faulting events. The 30 km thick syntectonic succession reflects deposition during two separate rifting events, which are disconnected by deposits reflecting a relative short period of tectonic quiescence. The results are discussed in light of examples of supradetachment basins on other rifted margins globally, as well as in the context of the evolution of the Norwegian margin overall.