Styles of extension offshore mid‐Norway and implications for mechanisms of crustal thinning at passive margins

Abstract

Eocene magmatic breakup along the mid‐Norway rifted margin was preceded by extreme Jurassic‐Cretaceous crustal thinning in a magma‐poor environment. Along the SE borders of the rift, “top basement” detachment faults with heaves on the order of 15–40 km evolved in at least two stages to become the boundaries between moderately thinned (20–30 km thick) crust and a 100–200 km wide, highly extended area with crustal thicknesses generally between 2 and 12 km under the present‐day Møre and Vøring basins. In the footwalls of the basin flank detachments, lower and middle crust was exhumed in extensional domes that became incised by a younger set of normal faults. Under the most highly thinned areas, a more distal set of deep‐seated (basin floor) detachments incised and extended remnant crust and, probably, the upper mantle, leaving as little as <5 km of continental crust to be preserved under thick synrift and postrift deposits. We suggest that basin flank detachments such as the ones described above hold the potential to reduce the crustal thickness down to the critical value required for embrittlement of continental crust. Thus, they prepare the ground for incision by the basin floor detachments, which may become responsible for exhumation of deep crust or continental mantle if extension is allowed to proceed.

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

“…Thus, one of the benchmarks of hyperextension identified in the Iberia-Newfoundland system, the exhumation of serpentinised mantle to the seafloor (Boillot et al, 1980;Manatschal et al, 2001;Whitmarsh et al, 2001), cannot be proven directly offshore Norway. Several workers have, however, discussed the possibility, and some have suggested that it may have occurred, based on interpretation of seismic reflection data, refraction data, potential field data and modelling (Ren et al, 1998;Osmundsen & Ebbing, 2008;Lundin & Doré, 2011;Reynisson et al, 2011;Péron-Pinvidic et al, 2012Rüpke et al, 2013). Others reject this possibility (e.g., Nirrengarten et al, 2014), or propose alternative solutions that involve bodies of dense, eclogite-facies, continental crust under the most highly thinned areas (Gernigon et al, 2004;Mjelde et al, 2012).…”

“…More recently acquired refraction data (Breivik et al, 2011;Kvarven et al, 2014) and potential field-based crustal models provide additional constraints (e.g., Ebbing et al, 2006;Ebbing & Olesen, 2010). Recent works on hyperextended margins elsewhere have presented a number of concepts that should be considered when discussing the Norwegian margin (e.g., Blaich et al, 1997;Osmundsen & Ebbing, 2008;Péron-Pinvidic et al, 2013). Basinward migration of rifting activity has been well documented in the hyperextended Iberian margin (e.g., Péron-Pinvidic et al, 2007;Sutra et al, 2013).…”

“…Further evidence for hyperextension offshore Norway was based largely on interpretation of lines from long-offset seismic reflection data, shot and recorded to 12 and 14 seconds twoway time (s twt) in the mid-1990s. Largely, arguments were based on the interpretation of large-magnitude extensional faults in what is now known as the necking domain as well as in the inner parts of the distal margin (Osmundsen & Ebbing, 2008;Péron-Pinvidic et al, 2013). This area coincides with areas where seismic refraction studies and potential field modelling (Faleide et al, 2008;Mjelde et al, 2009a, b) suggested a very dramatic reduction of the crystalline crust.…”

Evidence of Late Ediacaran Hyperextension of the Laurentian Iapetan Margin in the Birchy Complex, Baie Verte Peninsula, Northwest Newfoundland: Implications for the Opening of Iapetus, Formation of Peri-Laurentian Microcontinents and Taconic – Grampian Orogenesis

“…Müntener and Manatschal 2006;Bernoulli et al 2003) or may change over time from magmapoor to magma-rich (e.g. Osmundsen and Ebbing 2008 Manatschal 2004;Manatschal et al 2007Manatschal et al , 2011Sutra and Manatschal 2012). This final asymmetric phase of extension may be superimposed on an earlier phase of more symmetric extension (Huismans and Beaumont 2002) during which mantle detachments can form below both extending margins (e.g.…”

The Ocean – Continent Transition Zones Along the Appalachian – Caledonian Margin of Laurentia: Examples of Large-Scale Hyperextension During the Opening of the Iapetus Ocean

“…Müntener and Manatschal 2006) and hyperextension is not exclusive to magma-poor margins such as Iberia. For example the northeast Atlantic 'volcanic' margin was affected by hyperextension processes in the Late Jurassic -Early Cretaceous (Osmundsen and Ebbing 2008;Lundin and Doré 2011).…”