The Formation and Evolution of the Norwegian-Greenland Sea: A 25-Year Aeromagnetic Perspective

Magnetic data, along with their associated chrons, have played a crucial role in deepening our understanding of oceanic crust formation and seafloor spreading dynamics. Over the past 25 years, the Geological Survey of Norway has conducted extensive magnetic surveys, acquiring more than 172,846 km of new aeromagnetic profiles in the Norwegian-Greenland Sea (NGS). This contribution presents our latest regional compilation of the NGS, shedding light on the complex tectonic evolution of the region since the onset of continental breakup. The NGS witnesses diverse tectonic regimes and structural features, including sub-oceanic basins of different ages, microcontinents, and conjugate volcanic passive margins, between the Greenland-Iceland-Faroe Ridge in the south and the Arctic Ocean in the north. The new aeromagnetic compilation suggests that the highly magmatic breakup in the NGS was diachronous and initiated as isolated and segmented seafloor spreading centres. The early seafloor spreading system, initiating in the Early Eocene, gradually developed into atypical propagating systems, with subsequent breakup(s) following a step-by-step thinning and rupture of the lithosphere. Newly formed spreading axes initially propagated towards local Euler poles, died out, migrated or jumped laterally, changed their propagation orientation, or eventually bifurcated. The final line of lithospheric breakup may have been controlled by highly oblique extension, associated plate shearing, and/or melt intrusions before and during the formation of the Seaward Dipping Reflectors (SDRs). The Inner SDRs and accompanying volcanics formed preferentially either on thick continental ribbons or moderately thinned continental crust. The segmented and diachronous evolution of the NGS spreading activity is also reflected by a time delay of 1–2 Myrs expected between the emplacement of the SDRs imaged at the Møre and Vøring margins. Further north, the initiation of spreading that led to the formation of the Knipovitch Ridge began around C6 (~20 million years ago) within a distinct and oblique oceanic segment in the Fram Strait region. Magnetic observations indicate a broader continent–ocean transition, interpreted as exhumed lower continental material adjacent to the Barents Sea margin, which significantly reduces the mapped extent of the oceanic domain expected in the Fram Strait. This configuration also suggests the presence of a failed oceanic basin east of the Boreas Basin, which helps explain the resulting asymmetry in the spreading system. Meanwhile, several significant changes in spreading kinematics were recognised in the Norway Basin, with the first occurring in the Middle Eocene around 47 Ma (magnetic chron C21r), initiating rifting in the southern part of the Jan Mayen Microplate Complex. Inheritance and magmatism likely influenced the complex reorganisation of rifting, ultimately leading to the final dislocation of the Jan Mayen Microplate Complex from Greenland during the Late Oligocene/Early Miocene. The mechanism behind this final dislocation, likely triggered by overlapping rift systems, also raises questions about the controversial nature of crust and lithosphere stretching between the Faroes and Iceland.