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

Summary: Age and significance of Grenvillian and Silurian
orogenic events in the Finnmarkian Caledonides,
northern Norway1
F. Corfu, M. Gerber, T.B. Andersen, T.H. Torsvik, and L.D. Ashwal
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 U­Pb data ob-
tained by ID­TIMS (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 440­435
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.
Re´sume´ : Les concepts concernant l'origine des Cale´donides du Nord de la Norve`ge ont change´ rapidement au cours de
la dernie`re de´cennie en grande partie gra^ce a` l'application de me´thodes ge´ologiques et isotopiques modernes. Le pre´sent
article pre´sente des donne´es U­Pb obtenues par ID­TIMS (« isotope dilution ­ thermal ionization mass spectrometry »)


Source: Andersen, Torgeir Bjørge - Centre for Physics of Geological Processes & Department of Geosciences, Universitetet i Oslo


Collections: Geosciences