Contributions to Mineralogy and Petrology

, Volume 98, Issue 1, pp 13–23 | Cite as

U/Pb ages of ophiolites and arc-related plutons of the Norwegian Caledonides: implications for the development of Iapetus

  • G. R. Dunning
  • R. B. Pedersen


U/Pb zircon ages are reported for four ophiolites and three crosscutting arc-related plutons from the Norwegian Caledonides. Plagiogranite differentiated from gabbro of the Karmøy ophiolite is dated at 493+7/-4 Ma whereas arc-related trondhjemite cutting this ophiolite crystallized at 485+/−2 Ma. A crosscutting clinopyroxene-phyric gabbro intrusion is dated at 470+9/−5 Ma by near concordant magmatic titanite (sphene) and discordant U-rich (2903–6677 ppm) zircon. Lower intercepts of 247+/−68 and 191+/−70 Ma defined by the plagiogranite and clinopyroxene-phyric gabbro best-fit lines may reflect a real low-T alteration/rift-related event.

A plagiogranite differentiate of the Gullfjellet ophiolite complex is dated at 489+/−3 Ma and a crosscutting arc-related tonalite is 482+6/−4 Ma. Both of these ages overlap with those of the correlative rocks at Karmøy suggesting that they are parts of one ophiolitic terrane with a common history.

Trondhjemite associated with the Leka ophiolite is dated at 497+/−2 Ma, indicating that supra-subduction zone magmatism there may be coeval with spreading which formed the Karmøy axis sequence.

The U/Pb zircon ages of Norwegian ophiolites reported here, combined with ages of other Appalachian-Caledonian ophiolite complexes in Britain and Canada, indicate a narrow age range for the generation of at least two marginal basins in the Tremadoc-Arenig. Two spreading episodes documented at Karmøy are separated in time by intrusion of arc-related trondhjemite magmas at 485+/−2 Ma and may correlate with two separate spreading events documented in other ophiolites.

The Solund/Stavfjorden ophiolite, at 443+/−3 Ma, is the only late Ordovician ophiolite yet documented in the entire Appalachian-Caledonian Orogen and it probably represents a small, short-lived marginal basin late in the history of the Iapetus Ocean. It is correlative with Caradocian ensialic marginal basin magmatism in Wales and the Trondheim region, and with tholeiitic gabbro-diorite plutons that intruded Newfoundland ophiolites in a tensional regime after emplacement of the ophiolites over the continental margin.


Zircon Ordovician Continental Margin Titanite Marginal Basin 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag 1988

Authors and Affiliations

  • G. R. Dunning
    • 1
  • R. B. Pedersen
    • 2
  1. 1.Department of GeologyRoyal Ontario MuseumTorontoCanada
  2. 2.Geologisk Institutt Avd. AUniversitetet I BergenBergenNorway

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