3D evolution of extensional detachment faults and their effect on the architecture of rifts and rifted margins

Extensional detachment faults, core complexes and supradetachment basins play major roles in the evolution of 3D rifted margin architecture. The successive incision of basement from early to late stages in the margin evolution is rarely explained in 3D. One reason for this is likely the lack of a unifying model for how very large faults grow and link laterally, and how this, in turn, links to the temporal evolution of the margin. As fault shape exerts a fundamental control on syn-rift basin architecture, the 3D evolution of detachment faults is critical to understand sedimentation in associated basins.

In the proximal margin offshore Norway, one control on lateral variation appears to be the differential exploitation of `extraction´ structures that evolved above the ductile crust. This controlled flips in fault polarity under the proximal margin, and lateral transitions from supradetachment- to half-graben style, Late Paleozoic-Triassic basins. Extensional culminations and core complexes were associated with this deformation pattern at depth.

The growth of an extensional fault past a displacement of a few kilometers will involve a change in 3D fault shape related to the isostatic rollback of parts of the fault plane. As displacement magnitude varies along the fault plane, so will the amount of extensional unloading and associated isostatic compensation. With increasing extension this will enforce a particular shape on the fault plane, with an extensional culmination developing in the area of maximum displacement, and synclinal recesses evolving on the flanks. With continued extension, the culmination evolves into a core complex. Necking domains, where faults propagate into the ductile middle crust appear to be prime locations for this type of faulting. As large-magnitude faults combine into domain-bounding breakaway complexes, this results in intermittent occurrences of core complexes along the main breakaways and lateral transitions into steeper megafaults and fault arrays. At the Mid-Norwegian margin, we interpret the Jurassic-Cretaceous North Møre and south Vøring basins to illustrate this type of evolution. Components of strike-slip may modify this type of pattern, as illustrated by  continental core complexes exposed in areas such as Death Valley and western Norway.