The tectonomagmatic evolution of Svalbards North-Western Terrane. : U/Pb-ages for Proterozoic crust and Caledonian magmatic evolution in Spitsbergen.

Abstract

Combination of field studies and analytical techniques provides the basis for unravelling the tectonic evolution of the continental crust. Here field studies together with the ID-TIMS method for U/Pb-dating have been applied to a segment of the North Atlantic Caledonides, the NW Spitsbergen Terrane.

The archipelago of Svalbard is situated in the Arctic Ocean and comprises Caledonian and older basement rocks underlying a Devonian-Neogene sedimentary succession. The basement is composed of several terranes separated by N-S-trending faults.

Fieldwork and U/Pb dating on zircon, monazite and titanite from orthogneisses and granitoids from the NW Spitsbergen Terrane provides more detailed knowledge on the timing of 2 orogenic events in this region; the Grenvillian and the Caledonian. The Grenvillian event is represented by two samples of orthogneiss yielding crystallization ages of 962 ± 6 and 970 ± 7 Ma. Caledonian rocks dated include two samples of migmatite gneiss from the Kongsfjorden area yielding 425 ± 4 and 423 ± 1 Ma monazite ages, a migmatite leucosome (418,0 ± 0,7 Ma, Krossfjorden) and two granitoid intrusions from the Smeerenburgfjorden area with crystallization ages of 418,4 ± 0,7 and 421,6 ± 1,5 Ma. These data are in good agreement with previous interpretations that the NW Spitsbergen terrane has Laurentian affinities.