Using field observations, geochemistry and geochronology to evaluate if Svalbard comprises amalgamated displaced terrane

Svalbard and the western Barents Shelf is traditionally thought to comprise several disparate terranes that were formerly hundreds of kilometres apart and juxtaposed along transcurrent fault zones during the late Palaeozoic[1]. Recent studies, largely informed by reprocessed seismic datasets, has brought into question the magnitude of terrane displacement[2] because Precambrian–Cambrian geological features are inferred to continue across the bounding fault zones. This study aims to contribute to the debate on the paleogeographic position of the terranes through field observations, geochronology and isotope geochemistry on units sampled from four locations.

The Billefjorden Fault Zone in central Spitsbergen has a protracted history and separates the West Ny Friesland terrane from the Devonian Ny Friesland Basin and its concealed basement. U-Pb zircon geochronology of intensely sheared migmatitic gneisses demonstrate that these rocks have Palaeoproterozoic protoliths and correlate with the West Ny Friesland terrane. Migmatisation and granitoid intrusion accompanied shearing between 435–426 Ma and could be the cause of a prominent magnetic anomaly coinciding with the fault zone. This sequence of events suggests the pre-Caledonian position of the west Ny Friesland terrane was adjacent to east Greenland.

At Hornsund, southern Spitsbergen, metasediments and subordinate granitoid and volcanic units form the Southwestern Province (terrane) on the opposite margin of the Devonian basin. The volcanic and granitoid rocks yield late Mesoproterozoic U-Pb zircon ages. Rocks of this age are not recorded from east Greenland nor the Arctic realm. This may suggest a Baltican heritage for the Southwestern Province and indicate that its pre-Caledonian position was located at a considerable distance from the west Ny Friesland terrane.

These and the data from the two other study locations (Bjørnøya and the concealed basement of the southwest Barents Shelf), are most consistent with terrane models for the formation of Svalvard that can accommodate the translation and juxtaposition of disparate crustal blocks.

[1]Harland and Wright 1979, Norsk Polarinstitutt Skrifter, 167, 89–117; [2]Koehl et al. 2022, Solid Earth, 13, 85–115.