Summary Insights into the spreading evolution of the Knipovich Ridge and development of the Fram Strait are revealed from a recent aeromagnetic survey. As an ultra-slow spreading ridge in an oblique system located between the Svalbard—Barents Sea and the Northeast Greenland rifted margins, the dynamics of the Knipovich Ridge opening has long been debated. Its 90-degree bend with the Mohns Ridge, rare in plate tectonics, affects the evolution of the Fram Strait and motivates the study of crustal deformation with this distinctive configuration. We identified magnetic isochrons on either side of the present-day Knipovich Ridge. These magnetic observations considerably reduce the mapped extent of the oceanic domain and question the present understanding of the conjugate rifted margins. Our analysis reveals a failed spreading system before a major spreading reorganization of the Fram Strait gateway around magnetic chron C6 (circa 20 Ma).

New high-resolution aeromagnetic data from the Caledonides and Archaean-Palaeoproterozoic crystalline basement of Finnmark and North Troms derived from surveys conducted as part of NGU's MINN programme provide spectacular and confirmatory evidence for the continuation of diverse, Precambrian greenstone belts and granulite terranes beneath the magnetically transparent Caledonian nappes. Complementary airborne radiometric data collected in the same survey contribute to the analytical process and to an evaluation of the mineral potential in the area. Some parts of existing data have also been reprocessed using new techniques and software to reach the same level as the newly acquired data. The new compiled data provide images of the magnetic field at sufficiently high resolution to allow us to examine finer details of the bedrock geology. One of the principal outcomes of the analysis is a picture of the detailed structural fabric of the region provided by images of tilt derivatives of the magnetic field that enhance anomalies. This fabric is an important framework for developing exploration strategies. Patterns and other characteristics of the magnetic field have been used to revise positions of some geological boundaries, especially in poorly exposed areas, and delineate specific domains within northern Norway. Radiometric data have been used to supplement the magnetic interpretations in some cases. In general, there is a good correlation between the radiometric data and magnetic anomaly maps which can be utilised to re-evaluate the geological boundaries. Several such features of interest are discussed. As an example, NW-SE-trending, fault-bounded terranes or belts which extend from Finnmark and Troms through northern Finland, Sweden and Russia can be easily followed on the high-resolution data. In this contribution, all the main geological terranes from the Archaean-Palaeoproterozoic belt to the Caledonian nappes in northern Norway will be discussed in relation to their magnetic patterns and radiometric anomalies.

Abstract. With hundreds of metres of ice, the bedrock underlying Austfonna, the largest icecap on Svalbard, is hard to characterize in terms of topography and physical properties. Ground-penetrating radar (GPR) measurements supply ice thickness estimation, but the data quality is temperature dependent, leading to uncertainties. To remedy this, we include airborne gravity measurements. With a significant density contrast between ice and bedrock, subglacial bed topography is effectively derived from gravity modelling. While the ice thickness model relies primarily on the gravity data, integrating airborne magnetic data provides an extra insight into the basement distribution. This contributes to refining the range of density expected under the ice and improving the subice model. For this study, a prominent magmatic north–south-oriented intrusion and the presence of carbonates are assessed. The results reveal the complexity of the subsurface lithology, characterized by different basement affinities. With the geophysical parameters of the bedrock determined, a new bed topography is extracted and adjusted for the potential field interpretation, i.e. magnetic- and gravity-data analysis and modelling. When the results are compared to bed elevation maps previously produced by radio-echo sounding (RES) and GPR data, the discrepancies are pronounced where the RES and GPR data are scarce. Hence, areas with limited coverage are addressed with the potential field interpretation, increasing the accuracy of the overall bed topography. In addition, the methodology improves understanding of the geology; assigns physical properties to the basements; and reveals the presence of softer bed, carbonates and magmatic intrusions under Austfonna, which influence the basal-sliding rates and surges.

Hydrothermal circulation is a process fundamental to all types of mid-ocean ridges that largely impacts the chemical and physical balance of the World Ocean. However, diversity of geological settings hosting hydrothermal fields complicates the exploration and requires thorough investigation of each individual case study before effective criteria can be established. Analysis of high-resolution bathymetric and magnetic data, coupled with video and rock samples material, furthers our knowledge about mid-ocean-ridge-hosted venting sites and aid in the interpretation of the interplay between magmatic and tectonic processes along the axial volcanic ridges. The rock-magnetic data provide constraints on the interpretation of the observed contrasts in crustal magnetization. We map the areal extent of the previously discovered active basalt-hosted Loki's Castle and inactive sediment-hosted Mohn's Treasure massive sulfide deposits and infer their subsurface extent. Remarkably, extinct hydrothermal sites have enhanced magnetizations and display clear magnetic signatures allowing their confident identification and delineation. Identified magnetic signatures exert two new fossil hydrothermal deposits, MT-2 and MT-3. The Loki's Castle site coincides with negative magnetic anomaly observed in the 2-D magnetic profile data crossing the deposit. First geophysical investigations in this area reveal the complexity of the geological setting and the variation of the physical properties in the subsurface.