Integrated 3D geophysical and geological modelling of the Kautokeino Greenstone Belt in Finnmark, northern Norway

A new 3D crustal-scale model has been created for the Kautokeino Greenstone Belt (KKGB) in northern Norway based on 3D density modelling and aeromagnetic data, integrated with qualitative interpretation of geophysical and geological data. Detailed geophysical analyses and their integration with an existing petrophysical database allowed us to identify and interconnect shallow and deeper structures throughout the study area. To have better control on the regional tectonic setting of the KKGB, the model area has been extended to include the northern part of Finland and Sweden. The new 3D density model reveals that the KKGB is broader than supposed previously. The 3D analysis indicates that the belt reaches depths of approximately 5-6 km and is emplaced as a highly deformed structure between the Archaean Jergul Gneiss Complex (JGC) to the east and the Rommaeno Gneiss Complex (RoGC) in Finland to the west. The Raiseatnu Gneiss Complex (RaGC) in the western part of the KKGB is characterised by a dominant NNW-SSE magnetic trend that is sub-parallel to the main trend of the KKGB. Moreover, the RaGC is similar to the KKGB in terms of the presence of a large number of sub-parallel magnetic anomalies. This gneiss complex shows mostly short-wavelength anomalies and some circular anomalies that differ from the more subdued and irregular anomaly pattern of the JGC and RoGC. In the new 3D model, the RaGC is assumed to constitute a migmatised part of the Kautokeino Greenstone Belt. At a large scale, this Proterozoic greenstone belt has some similarities to Archaean counterparts, where most of the deformation is caused by gravitational tectonics. This study shows that careful integration of geological and geophysical data can strongly improve the 3D understanding of the complex, poorly exposed, Precambrian terranes of the Finnmarksvidda region in Norway.