Extension and magmatism in the Oslo rift, southeast Norway: No sign of a mantle plume

https://doi.org/10.1016/0012-821X(94)90276-3Get rights and content

Abstract

The Late Carboniferous-Permian (300–240 Ma) Oslo Graben in southeast Norway is a classical continental magmatic rift. About 8–12 km of mafic magma was produced during a period of 40–60 My. The mantle-derived rock volume is ∼ 3 × 105 km3, with an average melt production rate of ∼ 0.005 km3y−1. Initial subsidence and the onset of magmatism preceded graben formation by 5–10 My. Upper crust extension, inferred from dykes and faults, is ⩽ 10%, whereas the total crust appears to have been thinned by up to 30%. The mantle upwelled with a velocity < 2 mMy−1 and suffered conductive heat loss. Adiabatic melting models, therefore, do not apply. A melting model that takes into account syn-rift conductive cooling, depth-variable stretching and mantle composition, suggests that the lithospheric solidus must have been reduced relative to anhydrous peridotite and that mantle thinning should be greater than crustal stretching. The lithospheric affinity of primitive rocks, the initial subsidence, the absence of a hot spot track and the low magma production rate indicate that Oslo Graben magmatism was not associated with a mantle plume. We conclude that the Oslo Graben was more ‘wet’ than ‘hot’ and that extension and magmatism were caused by passive necking of the lithosphere.

References (51)

  • E.W. Mearns

    SmNd ages for Norwegian garnet peridotite

    Lithos

    (1986)
  • S. Pallesen

    Crustal extension in the Oslo Graben, SE Norway: a method incorporating magmatism and erosion

    Tectonophysics

    (1993)
  • T. Pedersen et al.

    Skagerrak evolution derived from tectonic subsidence

    Tectonophysics

    (1991)
  • H.E. Ro et al.

    A stretching model for the Oslo Rift

    Tectonophysics

    (1992)
  • L. Royden et al.

    Rifting process and thermal evolution of the continental margin of Eastern Canada determined from subsidence curves

    Earth Planet. Sci. Lett.

    (1980)
  • G. Calcagnile

    The lithosphere-asthenosphere system in Fennoscandia

    Tectonophysics

    (1982)
  • H. Fukuyama

    Heat of fusion of basaltic magma

    Earth Planet. Sci. Lett.

    (1985)
  • M. Liu et al.

    Evolution of Hawaiian basalts: a hotspot melting model

    Earth Planet. Sci. Lett.

    (1991)
  • F.R. Larsson et al.

    Crustal reflectivity in the Skagerrak area

    Tectonophysics

    (1991)
  • J.-P. Foucher et al.

    The ocean-continent transition in the uniform lithospheric stretching model: role of partial melting in the mantle

    Philos. Trans. R. Soc. London Ser. A

    (1982)
  • D.P. McKenzie et al.

    The volume and composition of melts generated by extension of the lithosphere

    J. Petrol.

    (1988)
  • N.T. Arndt et al.

    The role of lithospheric mantle in continental flood volcanism: Thermal and geochemical constraints

    J. Geophys. Res.

    (1992)
  • K. Gallagher et al.

    Dehydration melting and the generation of continental flood basalts

    Nature

    (1992)
  • R.S. White et al.

    Oceanic crustal thickness from seismic measurement and rare earth element inversions

    J. Geophys. Res.

    (1992)
  • R.S. White et al.

    Magmatism at rift zones: The generation of volcanic continental margins and flood basalts

    J. Geophys. Res.

    (1989)
  • Cited by (23)

    • U-Pb systematics in volcanic and plutonic rocks of the Krokskogen area: Resolving a 40 million years long evolution in the Oslo Rift

      2020, Lithos
      Citation Excerpt :

      The origins of the magmas are debated. For example, Pedersen and van der Beek (1994) argued that stretching and melting of a volatile-rich mantle lithosphere were responsible for magmatism in the Oslo Rift, also stressing that the absence of a hot-spot track, the initial subsidence, and the relatively low magma production rate did not support a mantle plume explanation. The production rate was estimated on the basis of 8–12 km of mafic magma produced during a period of 40–60 my.

    • Moho and magmatic underplating in continental lithosphere

      2013, Tectonophysics
      Citation Excerpt :

      The rift zone is regarded as a classic example of rifting and the presence of a high density “rift pillow” in the lower crust was interpreted by early gravity studies (Ramberg and Smithson, 1971). However, later studies favour wet mantle melting without control from a hot mantle plume (Pedersen and Vanderbeek, 1994) as indicated by the small volume of volcanics and lack of surface uplift before rifting (Heeremans et al., 1996). Yet, until the acquisition of seismic data, it has been impossible to assess the amount of magmatic additions to the crust.

    • Crustal structure and composition of the Oslo Graben, Norway

      2011, Earth and Planetary Science Letters
      Citation Excerpt :

      A high density “rift pillow” in the lower crust was interpreted by early gravity studies (Ramberg and Smithson, 1971). More recent studies favour a less typical, low temperature, wet mantle rift regime (Neumann et al., 1992; Pedersen and Van der Beek, 1994; Pedersen et al., 1998), and formation of the rift by impingement of a hot mantle plume has largely been discredited (Pedersen and Van der Beek, 1994). The key observations against the plume model are the insufficient volume of volcanics, and the lack of surface uplift prior to rifting (Heeremans et al., 1996).

    • Magma generation in an alternating transtensional-transpressional regime, the Kraków-Lubliniec Fault Zone, Poland

      2010, Lithos
      Citation Excerpt :

      However, the presence of a thermal anomaly beneath the European lithosphere in Permian times is a matter of debate. Ro and Faleide (1992) argue in favor of it whereas Pedersen and Van der Beek (1994) are skeptical. A weakly active mantle plume at the base of the lithosphere was inferred by Ziegler (1996).

    • Tectonic subsidence history and thermal evolution of the Orange Basin

      2010, Marine and Petroleum Geology
      Citation Excerpt :

      Observations supporting underplating occurring coevally with initial rifting include surface uplift, massive sand influx and the low subsidence rate during and after the break up (Maclennan and Lovell, 2002). The production of the required melts is still a matter of debate and may be a result of elevated potential temperature of the mantle, of high extension rates, of small-scale convection, or of fertile patches in the upper mantle (Boutilier and Keen, 1999; Buck, 1991; Foulger and Anderson, 2005; Korenaga, 2004; McKenzie and Bickle, 1988; Nielsen and Hopper, 2002; Pedersen and van der Beek, 1994; van Wijk et al., 2001; Wilson, 1993). It is beyond the scope of this study to discriminate between causative mechanisms.

    View all citing articles on Scopus
    View full text