Abstract
The role of inherited structures during the development of normal faults in continental rifts and proximal domains of passive margins have been extensively studied. Few studies, however, have a focus on deciphering the role of inheritance in the development of high-displacement (>10 km), low-angle (<30°) normal faults in necking domains of passive margins. We integrated and interpreted potential field, 2D and 3D reflection seismic, and well data to study the role of structural inheritance in controlling the location and development of the southern part of the Klakk Fault Complex, offshore mid-Norway. The down-to-the-west Klakk Fault Complex is an N-S non-collinear fault complex that separates the Frøya High in its footwall from the Rås Basin in its hanging wall. The fault segments vary from low-angle planar to listric fault geometries in cross-section, with displacements of 17 km–34 km. These displacements led to syn-rift basement thinning of 12–14 km toward the west, which consequently, also affected the crustal wedge geometry of the necking domains. We identify three intra-acoustic-basement structures based on seismic facies and define their 3D geometry: (i) a bowl-shaped basin, (ii) a hyperbolic surface, and (iii) a domal structure. We discuss their origin and elucidate their role during later rifting. We conclude that pre-existing basement structures controlled the rift-related structures during the second rift phase (thinning), and affected the location, geometries, orientation and segmentation of the high-displacement low-angle faults in the necking domains. The results of this work offer new insights into the development of necking domains in areas where a thick continental crust (>25 km) is present during rifting.
Highlights
We focus on the southern part of the Klakk Fault Complex (Klakk FC), which is located in the southern transition between the Møre and Vøring margin segments of the Norwegian Passive Margin (Mosar, 2003) (Fig. 2a)
Inherited structures in continental rifts and rifted margins are generally defined as pre-rift basement structures such as continental metamorphic core complexes, continental supradetachment basins, shear zones, ancient thrust or normal faults, and pervasive basement fabrics (e.g. Reeve et al, 2014; Phillips et al, 2016; Fazlikhani et al, 2017; Lenhart et al, 2019)
We discuss the nature of the three intra-basement structures identi fied based on (i) the character of the intra-basement seismic facies, (ii) the location and geometry of the seismic facies, (iii) the geometries of the structures identified and (iv) the correlation with nearby intrabasement structures that are described in the literature (e.g. Osmund sen et al, 2002; Phillips et al, 2016; Fazlikhani et al, 2017; Lenhart et al, 2019)
Summary
The magma budget, development and final geometry of continental rifts and rifted margins are controlled by the interplay between struc tural inheritance and extensional tectonics, along with such factors as the strength, thickness, composition, and thermal structure of the crustal lithosphere (Dore et al, 1997; Chenin et al, 2015; Manatschal et al, 2015; Rotevatn et al, 2018; Salazar-Mora et al, 2018; Schiffer et al, 2019). High-β ‘type 0’ faults (type HB0 late-to post-orogenic detachment) are detachment faults associated with the evolution of metamorphic core complexes and supradetachment basins generated during late-to post- contractional stages of the Caledonian orogenic events, which are preserved in the proximal domains of the margin (Braathen et al, 2000; Fossen, 2010; Gee et al, 2010; Corfu et al, 2014) These faults display listric, subhorizontal or convex geometries in cross-section with dis placements of up to 100 km. (iii) High-β ‘type 2’ faults (type HB2: exhumation detachment) are low angle (
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