Thomas Brian Phillips, Christopher Aiden-Lee Jackson , James Norcliffe

Inversion may localise along pre-existing structures within the lithosphere, far from the plate boundaries along which the causal stress is greatest. Inversion style and magnitude is expressed in different ways, depending on the geometric and mechanical properties of the pre-existing structure. A three-dimensional approach is thus required to understand how inversion may be partitioned and expressed along structures in space and time. We here examine how inversion is expressed
along the northern margin of the Farsund Basin during Late Cretaceous inversion and Neogene uplift. At the largest scale, strain localises along the lithosphere-scale Sorgenfrei-Tornquist Zone; this is expressed in the upper crust as hangingwall folding, reverse reactivation of the basin-bounding normal fault, and bulk regional uplift. The geometry of the northern margin of the basin varies along-strike, with a normal fault system passing eastward into an unfaulted ramp. Late Cretaceous compressive stresses, originating from the Alpine Orogeny to the south, selectively reactivated geometrically simple, planar sections of the fault, producing hangingwall anticlines and causing long-wavelength folding of the basin fill. The amplitude of these anticlines decreases upwards due to tightening of pre-existing fault propagation folds at greater depths. In contrast, Neogene shortening is accommodated by long-wavelength folding and regional uplift of the entire basin.
subcrop mapping below a major, Neogene uplift-related unconformity and bore-based compaction analysis show that uplift increases to the north and east, with the Sorgenfrei-Tornquist Zone representing a hingeline to inversion rather than a focal point, as was the case during the Late Cretaceous. We show how compressional stresses may be accommodated by different inversion mechanisms within structurally complex settings. Furthermore, the prior history of a structure may also influence the mechanism and structural style of inversion that it experiences.