Complex fault patterns, transtension and structural segmentation of the Lofoten Ridge, Norwegian margin: Using digital mapping to link onshore and offshore geology

An integrated onshore-offshore study involving regional to outcrop-scale fault analysis is used to develop a self-consistent structural model for transtension along the Lofoten Ridge. The Lofoten-Vesterlen archipelago (LVA) is a segmented basement high showing distinct lateral variations in trend, deformational style, and structural complexity. This study investigates whether segmentation can be linked to differences in the obliquity of preexisting structures relative to plate movement vectors. Regional analysis of fault lineament patterns using Geographic Information Systems (GIS) reveals that the LVA can be subdivided into a series of distinct lineament domains. These domains are closely coincident with changes in ridge trend and variations in structure within offshore models derived from seismic reflection studies. Digital field mapping and spatial analysis of faulting in the north Lofoten reveal that multimodal faulting is dominated by transtensional dip-slip and oblique-slip movements which are comparable to analogue models where the ridge axis is 30 oblique to regional extension. The overall change in fault orientation, fault geometry, and deformation style are consistent with models for transtension where the ridge-bounding structure becomes increasingly oblique to regional extension. Previously identified transfer zones simply reflect segment domain boundaries and are not reactivating basement structures. This model is a possible analogue for other orthogonal and oblique rift structures on the Norwegian and other margins.