Field observations and 40Ar/39Ar isotopic dating indicate that eclogites exposed in the Lofoten Islands, north Norway, formerly presumed to be Proterozoic features, most likely formed as a result of early to middle Paleozoic, i.e., Caledonian, metamorphism. The Lofoten eclogites occur in shear zones that cut Baltic Precambrian continental basement. This unusual style of occurrence is shared only with Caledonian shear-zone eclogites of the allochthonous Bergen arcs of western Norway. Our findings help to link Scandinavian eclogites with those on the Laurentian side of this collisional zone in East Greenland. Ordovician to Silurian eclogites also are found locally throughout the southern, Appalachian continuation of the orogen in eastern North America. We compare the pressures, ages, and tectonic and structural settings of the eclogites along the ∼10,000 km length of the Appalachian-Caledonian system. Our synthesis supports the idea that Laurentian Taconic elements may be preserved in high-level nappes in Norway. The rare, deep-crustal metamorphic relicts also appear to be shared between Baltica and Laurentia, offering a new perspective in which to view the geodynamic evolution of this once-Earth-spanning orogenic system.

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