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Regional Relationships and Correlations |
1 Laboratory for Isotope Geology, Swedish Museum of Natural History, Box 50 007, SE-104 05 Stockholm, Sweden ake.johansson{at}nrm.se
2 Now at Centre of Isotopic Research, Russian Geological Institute (USEGEI), St Petersburg, Russia ake.johansson{at}nrm.se
3 Department of Geophysics, Uppsala University, Villavägen 16, SE-752 36 Uppsala, Sweden ake.johansson{at}nrm.se
4 Norwegian Polar Research Institute, c/o IASC, Postboks 5156 Majorstua, N-0302 Oslo, Norway ake.johansson{at}nrm.se
5 Polar Marine Geological Expedition, Pobeda street 24, Lomonosov 189 510, Russia ake.johansson{at}nrm.se
The Nordaustlandet Terrane of NE Svalbard forms an exposed part of the Barentsia microcontinent. Augen gneisses, migmatites, granites and gabbros dominate the scattered outcrops along the northeastern coast of Nordaustlandet, and on the smaller islands to the north and east, as far as Kvitøya. These outcrops probably represent the deepest exposed crustal levels within the folded Caledonian basement of the Nordaustlandet Terrane. In the present study, a variety of rock types have been analysed by different U-Pb dating techniques (conventional, Pb-evaporation and ion microprobe) on zircon, titanite and monazite The major and trace element compositions and Sm-Nd isotope geochemistry of these rocks have also been investigated.
The augen gneisses yield U-Pb ages of c. 950 Ma, indicating that they are deformed late Grenvillian granites, similar to the Grenville-age granites and augen gneisses of northwestern and central Nordaustlandet. Migmatites, grey granites, aplitic dykes and a syenite (boulder) yield U-Pb ages mainly falling in the 430–450 Ma range, slightly older than the 410–420 Ma late-tectonic Caledonian granites further west. Both the Grenvillian and Caledonian granites are of crustal anatectic origin, and the Caledonian granites and migmatites may have formed largely by remelting of Grenvillian crust. The ages of the mafic rocks are uncertain, but Sm-Nd data indicate a possible emplacement age of c. 700 Ma for two of the gabbros, suggesting that they may be the result of rift-related magmatism in connection with the opening of the Iapetus Ocean. A few enigmatic inherited zircons of similar late Neoproterozoic age found in younger granites may possibly be related to this event. No evidence for late Neoproterozoic orogenic activity, similar to that in the Timanides of northern Russia, is seen in eastern Svalbard. At this time, eastern Svalbard (Barentsia) was probably part of the Laurentian margin, and probably located far away from northern Baltica.
