Age and significance of Grenvillian and Silurian orogenic events in the Finnmarkian Caledonides

• Main Authors: Northern Norway, F. Corfu, M. Gerber, T. B. Andersen, T. H. Torsvik, L. D. Ashwal
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Kalak; Norway; Northern Norway
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.664.1712; http://earthdynamics.org/papers-ED/2011/2011-Corfu-etal_CJES.pdf

Abstract: The concepts concerning the origin of the Caledonides of northern Norway have changed rapidly in the last dec-ade thanks largely to the application of modern geological and isotopic methods. This contribution presents U–Pb data ob-tained 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 Gren-villian 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 gab-broic 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 underly-ing Kalak Nappe Complex were juxtaposed on Baltica by that time. The age structure and other geological and paleomag-netic 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 obli-que convergence of Baltica and Laurentia. Résume ́ : Les concepts concernant l’origine des Calédonides du Nord de la Norvège ont change ́ rapidement au cours de la dernière décennie en grande partie grâce a ̀ l’application de méthodes géologiques et isotopiques modernes. Le présent