Detachment Faulting, Successive Incision and Controls on Supradetachment Basin Formation at the Mid-Norwegian Rifted Margin

Detachment fault systems recording displacements in the order of 10s to 100s of km remain poorly understood compared to smaller scale normal faults. The evolutionary models developed for the growth and interaction of Andersonian-type faults are not fully applicable to these large-magnitude systems. Consequently, the associated basins - the so-called supradetachment basins - are still poorly understood compared to extensional half-graben basins.

Numerical and analogue 2D modelling have shed light on the mechanisms of footwall back-rotation during progressive extension (rolling hinge model; e.g. Lavier et al., 1999) but the along-strike evolution of such large-scale detachment systems remain poorly understood. It has been proposed that with increasing amounts of extension, detachment faulting favors formation of isostatically induced, longitudinal and transverse folds and consequently basin inversion in the area of maximum displacement (e.g. Kapp et al., 2008; Osmundsen & Péron-Pinvidic, 2018). The 4D configuration of the associated supradetachment basins is then controlled by the growth and (potential) lateral linkage of such faults - which may result in complex geometries.

In this study, we use interpretation of 3D- and 2D seismic reflection data from the necking domain of the Mid-Norwegian rifted margin to discuss the effects of lateral interaction and linkage of extensional detachment faults. The study area demonstrates how successive incision of such master faults may induce a complex structural relief in response to extensional detachment faulting and folding. In the inner parts of the south Vøring and northeastern Møre basins, the Klakk and Main Møre Fault Complexes form the outer necking breakaway complex and the western boundary of the Frøya High. The central Frøya High contains remnants of a metamorphic core complex, which we interpret as an extension parallel turtleback-structure. The turtleback is flanked two main synclinal depocenters constituting a supradetachment basin, whose location corresponds to the crustal taper break associated with the outer necking domain. We attribute the turtleback exhumation to Late Jurassic-Early Cretaceous detachment faulting along the Klakk and Main Møre Fault Complexes. Southwest of the Frøya High, the supradetachment basin links the Frøya High Turtleback with the core complex previously interpreted for the Gossa High, near where the Main Møre Fault Complex incises the Slørebotn detachment. The Slørebotn Subbasin consequently forms a synclinal keel basin with rafted blocks, a structural configuration which is recognizable also north of the ‘Frøya High Turtleback’ towards the Halten Terrace. We find that the pre-rift structural template and crustal heterogeneity facilitated differential supradetachment basin configuration during and after Late Jurassic-Early Cretaceous rifting, and that the supradetachment basin architecture was likely controlled by localized isostatic uplift, lateral linkage and successive incision of large-magnitude normal faults.