Abstract

The concepts concerning the origin of the Caledonides of northern Norway have changed rapidly in the last decade thanks largely to the application of modern geological and isotopic methods. This contribution presents U–Pb data obtained by ID–TIMS (isotope dilution – thermal ionization mass spectrometry) on zircon, titanite, and monazite from plutonic and metamorphic rocks. The Gjesvær Migmatite Complex of the Kalak Nappe Complex is shown to be of Grenvillian age, with granite and leucosome emplaced at about 970 Ma in a succession of psammites and amphibolites. It then underwent metamorphism and partial melting at about 425 Ma during Caledonian thrusting. Dating of granitic and gabbroic rocks that intrude the mainly turbiditic Hellefjord Group of the overlying Magerøy Nappe yields ages of 440–435 Ma, confirming that this unit is a correlative of the rocks on the island of Magerøy. A superimposed set of events at 430–425 Ma caused metamorphism forming pegmatites and local leucosome proving that the Magerøy Nappe, and the underlying Kalak Nappe Complex were juxtaposed on Baltica by that time. The age structure and other geological and paleomagnetic constraints suggest that the nappes originated along the Laurentian and perhaps Gondwanan margins and were brought to intersect Baltica by Cordilleran-type terrane translations along sinistral transform fault systems during the oblique convergence of Baltica and Laurentia.

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