| | |
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 »)
|
