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Geophysical interpretation of the continuation
The Skagerrak gravity and magnetic anomalies are situated in the Norwegian-Danish Basin just offshore southern Norway. A gravity high is partly coinciding with magnetic lows. The origin of these anomalies has been a matter of debate for almost three decades. Most geoscientists have advocated a Permian age for the source rock bodies, but a Tertiary age has also been suggested for the so-called 'Skagerrak volcano'. Modelling of aeromagnetic and gravity data shows that there is overwhelming evidence for a Sveconorwegian age of these anomalous rock bodies. They represent consequently a southwestward continuation of the Rogaland Igneous Province. We will within the present project study the offshore continuation of the Rogaland Igneous Province in more detail. An interpretation of the ILP (Mobil Search) profile 11 will also be included. We will publish the results in a paper for Techtonophysics. The E-W trending Lyngdal granite on the coast 20 km to the north of the Skagerrak anomalies is an eastward extension of the Rogaland Igneous Complex and coincides with an E-W trending aeromagnetic grain. This anomaly is continuous with the positive part of the Skagerrak aeromagnetic anomaly and we suggest that the anomalies are caused by rocks of the Rogaland Igneous Complex and its offshore extension. Both the negative aeromagnetic anomaly and the positive gravity anomaly can be modelled using constraints from seismic reflection lines and available density data and rock-magnetic properties. A 7 km thick complex of ultramafic/mafic intrusives is located below a southward dipping 1-4 km thick section of Mesozoic sediments and 1-2 km of Palaeozoic sediments. The enormous body of ultramafic (or mafic) rock implied by the modelling could be the residue of the parental magma that produced the voluminous Rogaland anorthosites. These intrusions and other similar anorthosites around the world are interpreted to result from the differentiation of a mafic magma.
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