U–Pb ages of the Dalsfjord Complex, SW Norway, and their bearing on the correlation of allochthonous crystalline segments of the Scandinavian Caledonides
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The Dalsfjord Complex is an allochthonous crystalline unit in the hanging wall of a major extensional detachment of the Caledonian orogen on the western coast of Norway. U–Pb geochronology has been carried out to test a previously proposed correlation between this unit and the Jotun Nappe Complex, a member of the Middle Allochthon now occupying a foreland position to the east. A monzonite sample of the Dalsfjord suite yields a zircon age of 1,634±3 Ma, whereas a crosscutting gabbro was formed at 1,464±6 Ma. Both rocks were strongly overprinted during the Sveconorwegian orogeny, especially the monzonite whose zircons U–Pb data were strongly pulled towards a lower intercept age of 882±29 Ma, and whose titanite indicates a two-stage growth history at >960 Ma and <920 Ma. These relationships support the correlation of these units with the Jotun Complex, and to some degree also with the Lindås Nappe in the Bergen Arcs.
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