Extension, hyperextension and mantle exhumation offshore Norway: a discussion based on 6 crustal transects

Abstract

In spite of its classification as `magmatic´, the rifted margin off Mid Norway evolved as a hyperextended margin in Late Jurassic and Cretaceous time, with a pre-breakup structural evolution that resembles that of magma-poor margins. Because the distal margin was not drilled to crystalline basement, considerable uncertainty exists with respect to the distribution of lithologies at depth. In this contribution, we discuss the implications of various scenarios for deep-seated lithologies and evaluate the possibilities for mantle exhumation in the deep margin offshore Norway. A suite of JurassicCretaceous, very large-magnitude, extensional faults that exhumed successively deeper structural levels seawards are well imaged in recent long-offset seismic reflection data. Based on these key profiles, we document the structural configuration that created the extremely sharply tapered south Møre margin as well as subhorizontal detachment faults in the distal Vøring margin. The latter were associated with rotated extensional allochthon and supradetachment basins and contributed to the exhumation of very deep levels including rocks from the lower crust and/or upper mantle. In the outer margin, truncation and excision of this system by a new set of incising detachment faults occurred later in the Cretaceous and the earliest Cenozoic. We discuss the relationships between these detachment systems under the distal and outer margins and positive structural features such as the Rån and Gjallar ridges. The interpretation of basement lithologies at depth in the distal margin is ambiguous due to overlap in physical properties. Based on a process-oriented evaluation of the different interpretation scenarios, we favour a model where mantle windows were exhumed in the footwalls of some of the master faults in the Cretaceous.

Cretaceous‐Paleocene Evolution and Crustal Structure of the Northern Vøring Margin (Offshore Mid‐Norway): Results from Integrated Geological and Geophysical Study

“…The density expected at the level of the ULCB is so high (3,200 kg/cm 3 ) and so massive that we disregarded the possibility of preserved deep sediments at that level. This is in contradiction with recent alternative assumptions from Osmundsen et al (). Shallow magnetic source estimations (Figure b) also support the presence of magnetic (basement) rock at 10–15 km and accordingly cannot easily explain the presence of Mesozoic sediments at that level.…”

“…The density expected at the level of the ULCB is so high (3,200 kg/cm 3 ) and so massive that we disregarded the possibility of preserved deep sediments at that level. This is in contradiction with recent alternative assumptions from Osmundsen et al (2016). Shallow magnetic source estimations Tectonics 10.1002/2017TC004655…”

Crustal‐Scale Fault Interaction at Rifted Margins and the Formation of Domain‐Bounding Breakaway Complexes: Insights From Offshore Norway

“…Along many rifted margins, the gross‐scale structure changes considerably along strike (e.g., Péron‐Pinvidic et al, ; Stica et al, ), as shown also for the Norwegian margin by many workers (e.g., Blystad et al, ; Faleide et al, ; Osmundsen et al, , ; Tsikalas et al, , ). However, many margins can be subdivided into domains that share fundamental structural‐morphological characteristics (Péron‐Pinvidic et al, ).…”

“…Transect locations in Figure . For detailed descriptions of the transects and discussions of alternative interpretation scenarios see Osmundsen et al (). The margin architecture changes significantly from the south Møre to the Central Vøring basin.…”

The Role of Inherited Lithospheric Heterogeneities in Defining the Crustal Architecture of Rifted Margins and the Magmatic Budget During Continental Breakup

“…The COT, where breakup volcanics are found, is bounded to the east by a 100‐ to 200‐km wide continental domain of highly extended crust (i.e., 2‐ to 12‐km thick). Low‐angle detachments, similar to the ones observed in the Iberia margin, are believed to control the coupled stretching of the crust and the subcontinental mantle, which may have become exhumed if extension had continued (Osmundsen et al, ; Osmundsen & Ebbing, ; Péron‐Pinvidic et al, ).…”