Deciphering the Plate Tectonic Evolution of the Varanger Peninsula from Igneous Geochemistry and Geophysics | Uttydande av Varangerhalvöns tektoniska utveckling med hjälp av geokemi och geofysik
2024
Bergsjö, Mattias
The Varanger Peninsula in northern Norway is made up of two geological units of metasedimentary sequences, the Barents Sea Region and the Tanafjorden-Varangerfjorden Region. The two units are divided by a large, NW-SE oriented strike slip fault zone called the Trollfjorden Komagelva Fault Zone. Mafic intrusions in the form of dyke swarms have been emplaced into the metasedimentary sequences on both sides of the fault zone. Three different dyke swarms have been described and dated: One Devonian aged swarm on the eastern side of the peninsula, one of Ediacaran age in the north and one from the Carboniferous along the fault zone and continuing westward off the peninsula. Geophysical modelling of the two geological units shows evidence of strike slip movement along the TKFZ as well as deeper structures suggesting thrusting as well. Geochemical analysis of dykes in two sampling locations, the villages Kongsfjord and Båtsfjord, indicate that the dykes consist mainly of basalts based on very low silica and alkali contents. They are tholeiitic in nature and show some similarities to crustal sources based on trace element data. Chemical analyses also show that the two sampling locations differ from each other chemically. Comparison within the two, as well as to legacy data reveals different kinds and intensity of alteration and crustal assimilation. Finally, a comparison with similarly aged mafic rocks on southwestern Spitsbergen Island, Svalbard, shows that there is most likely no connection between the two spatially, as the geochemical data from Varanger and those of Svalbard do not generally share trends in any analysis, suggesting that, tectonically, the two terranes were not connected at the point of the mafic intrusions in either region.
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