Interpretation of depth to the magnetic basement in the northern Barents Sea (south of Svalbard)

Abstract Aeromagnetic data covering some 135,000 km 2 with 34,000 km of profiles in the northern Barents Sea (south of Svalbard) have been interpreted. The survey area is situated between 74° 30′ and 78°N, and 15° and 32°E. The main result of the study is a contour map of the depth to the top of the magnetic basement, indicating the thickness of the sedimentary rocks in the area. Three different graphical techniques and the autocorrelation method have been applied to determine the depths to magnetic sources from the profile data. The different methods yield errors which generally vary between 5% and 15%. Systematic errors will add to the spread shown by the different methods. Therefore, the inaccuracy of individual point estimates can sometimes be as large as 30%. The interpreted depths to the magnetic basement exceed 10 km in the Sorkapp Basin, in parts of Storfjorden, and towards the Olga Basin. The basement is located at depths of less than 2 to 3 km on the Bjornoya-Sorkapp High and the Hopen High, and at depths of about 6 km on the Gardar-banken High. Depths in the area of the central platform vary smoothly and gradually from 6 to 9 km. It is suggested that in some areas pre-Permian sediments may constitute more than half of the total sedimentary column. The location of the continent-ocean transition zone has been interpreted from the aeromagnetic data. Strong gradients in the contour map of depth to magnetic basement coincide with the well-known Bjornoya-Sorkapp Fault Zone. The strongest gradients seen elsewhere in the depth to basement map may therefore reveal major basement faults and/or flexures which define the margins of structural highs and troughs. In the Tertiary, the continental crust in the western part of the study area was deformed along NNW-SSE trending fault zones. These faults are sub-parallel to linear positive magnetic anomalies observed in the same area which reflect trends within the basement, and sub-parallel to major tectonic lines (including basement faults) mapped by geologists further to the north, on Spitsbergen. It is therefore inferred that (Precambrian?) basement fault or fracture zones have been reactivated in Phanerozoic times. East of a major tectonic line running N-S to NW-SE through the central part of the area, the basement map and the aeromagnetic map show variable trends, with NE-SW trends dominating. Comparison with deep seismic reflection data suggests that the interpreted discontinuity may represent a major Caledonian compressional structure (perhaps the Iapetus suture) which separates two different crustal terranes.