North Atlantic sea-floor spreading rates: implications for the Tertiary development of inversion structures of the Norwegian–Greenland Sea

Abstract

The Tertiary development of the Norwegian continental margin was dominated by the opening of the Arctic-North Atlantic Ocean. The correct identification of magnetic anomalies and their ages and the analysis of spreading rates during the formation of this ocean are important in understanding the development of the region and specifically the history of its passive margins. Three ocean domains, the AEgir, Reykjanes and Mohns regions, were investigated in an effort to understand the lateral changes in structural development of the passive margin after continental break-up. Spreading rates generally slowed down from 2 cm a À1 after Early Eocene initiation of sea-floor spreading, to values around 0.5 cm a À1 in Oligocene time. An increase in spreading rates to around 1 cm a À1 coincided with the positioning of the Iceland hotspot under the North Atlantic mid-ocean ridge. At the same time, the European plate changed its absolute plate motion from a north-directed drift to a motion more towards the east. The location of inversion structures in the Vøring and Faeroes Basin rather than in the Møre Basin is related to differences in spreading rates. The Mohns and the Reykjanes Ridges produced more ocean floor than the AEgir-Kolbeinsey Ridges. Asymmetric ocean-floor formation in the AEgir Ridge led to differential stress at the base of the lithosphere, which probably explains the absence of inversion features in the Møre Basin (less mantle drag). Furthermore, upper plate margins such as the Vøring Basin and possibly the Faeroe Basin have a lower compressional strength than lower plate margins such as the Møre Basin, and therefore preferentially developed inversion structures. Along the transform boundaries separating the domains, additional stress probably built up along extension of the transform zones into the extended continental crust. This additional stress probably also assisted initiation of the inversion structures in the Vøring Basin and the Faeroes area. The amplification of the inversion structures in the Vøring Basin and the Faeroes Basin was subsequently caused by a variety of processes related to sedimentation and uplift-erosion.

Understanding melt generation beneath the slow-spreading Kolbeinsey Ridge using 238U, 230Th, and 231Pa excesses

“…The Kolbeinsey Ridge is a shallow, slow-spreading ridge ($1.8 cm/yr; Mosar et al, 2002) extending northwards from Iceland at 66.5°N to the Jan Mayen Fracture Zone at 71°N ( Fig. 1 and Table 1).…”

“…Among global mid-ocean systems, the slow-spreading Kolbeinsey Ridge ($1.8 cm/yr; Mosar et al, 2002) north of Iceland represents Klein and Langmuir's (1987) shallow end member, due to its shallow ridge axis (mean depth $1100 m). Relative to other MORB, the Kolbeinsey Ridge erupts basalts that are highly depleted in trace elements and have both low Na 8 , suggesting large degrees of melting, and high Fe 8 , suggesting deep initiation of melting (Klein and Langmuir, 1987).…”

East Greenland Ridge in the North Atlantic Ocean: An integrated geophysical study of a continental sliver in a boundary transform fault setting

“…[2] The Norwegian-Greenland Sea and its continental margins ( Figure 1) have been subject to extensive geophysical studies since the first plate model was proposed by Talwani and Eldholm [1977], e.g., Myhre et al [1982], Hagevang et al [1983], Vogt [1986], Torsvik et al [2001aTorsvik et al [ , 2001bTorsvik et al [ , 2002, Mosar and Opsal [2002], Mosar et al [2002aMosar et al [ , 2002b, Lundin and Doré [2002], Lundin [2002], Tsikalas et al [2002], Faleide et al [2004], Engen [2005], Engen et al [2006Engen et al [ , 2008, and Olesen et al [2007]. The Norwegian Sea, SW Barents Sea and Svalbard margins are well-studied with extensive deep seismic studies [e.g., Faleide et al, 1991;Mjelde et al, 1997Mjelde et al, , 1998Mjelde et al, , 2002aMjelde et al, , 2005Ritzmann et al, 2002Ritzmann et al, , 2004Breivik et al, 2003Breivik et al, , 2006.…”

The origin of the asymmetry in the Iceland hotspot along the Mid-Atlantic Ridge from continental breakup to present-day

“…3). During 43-28 Ma, seafloor spreading at the AR was probably slower than at the RR and MR by as much as 30% (Breivik et al, 2006;Mosar et al, 2002;Smallwood and White, 2002;Voss et al, 2009), likely related to lithospheric stretching or the very earliest stages of rifting at the KR. Crustal thickness generated from 43 to 28 Ma along the middle and northern portions of the AR was only 3.5-5.5 km (Breivik et al, 2006), similar to that of normal (not hotspot influenced) oceanic crust at the same ultra-slow spreading rate of ∼7 km/Myr (Dick et al, 2003;White et al, 2001).…”

“…Geological estimates of the spreading rates at MR (Breivik et al, 2009;Voss et al, 2009), RR (Smallwood and White, 2002), AR (red, Breivik et al, 2006), and KR (yellow, Mosar et al, 2002) were averaged to create a mean North Atlantic spreading rate through time (black). Since 33 Ma, spreading rates by Mosar et al (2002) for all four ridges are incorporated. The mean spreading rate (black) was used to model all of the active ridges at times when the geological estimates of their spreading rates were very similar (deviating by <2 mm/yr).…”