Paper No. 11
Presentation Time: 9:00 AM-6:00 PM
IMPLICATIONS OF U-PB DETRITAL ZIRCON ANALYSIS OF METASEDIMENTARY COVER SEQUENCES ACROSS THE NORTHERN SCANDINAVIAN CALEDONIDES (68.5ON)
U-Pb LA-ICPMS detrital zircon ages are reported for siliciclastic cover units to basement exposed across the Caledonian orogen of northern Scandinavia. Three samples from the Neoproterozoic-Cambrian Dividal Group in the foreland show a strong 1.95-0.9Ga population and a weaker one at 2.8-2.6Ga; the former is compatible with Svecofennian (1.95-1.75Ga), Transcandian Intrusive belt (1.8-1.65Ga), and Sveconorwegian (1.7-0.9Ga) sources while the latter correlates to Archaean basement underlying much of northern Fennoscandia. Two of the samples have a strong and narrow population at 570Ma interpreted as detritus from the Timanian orogen in northernmost Norway and Russia. From the external Rombak window, one sample has predictable age peaks at 2.7Ga and 1.8Ga, whereas another has a single peak at 2.7Ga suggesting a supracrustal sequence that is pre-1.8Ga but post- 2.7Ga. The West Troms and Lofoten-Vesteralen terrane is a large mostly plutonic (Archaean to Paleoproterozoic) internal basement window over-ridden by east-directed Caledonian thrusts containing structurally dismembered metasedimentary sequences some of undetermined tectonic heritage. A sample from the Storvann Group, interpreted as the kyanite-grade cover to Baltica, contains age populations at 2.7Ga, 1.8Ga, and 1.4-1.6Ga apparently verifying this assignment. A sample from the Gullesfjord group is dominated by 1.4-0.9Ga ages (~90%) with minor populations 1.85Ga and 2.5Ga. Similarities between the Gullesfjord and Dividal group age profiles imply their correlation, the former likely being a deeply subducted counterpart to the latter. Our most outboard sample, from the Leknes Group, has an age population of 1.2-0.9Ga and a stronger one at 450-700Ma reflecting exotic (Laurentian) heritage.