HR: 0830h
AN: T31F-0896    [PDF]
TI: Orogenic Structures and Palaeozoic Basins Imaged by Potential Field Modelling
AU: * Lyngsie, S
EM: stig@lyngsie.nu
AF: Geological Institute, University of Copenhagen, Oester Voldgade 10, Copenhagen, 1350 Denmark
AU: Thybo, H
EM: ht@seis.geol.ku.dk
AF: Geological Institute, University of Copenhagen, Oester Voldgade 10, Copenhagen, 1350 Denmark
AB: Potential field data (gravimetric and magnetic) in the North Sea area is analysed with respect to identification of large scale lineaments, graben structures, intrusive complexes and Palaeozoic basins. Edges of magnetic sources are outlined by calculation of the horizontal gradient from the pseudogravity field and correlated with the observed gravity anomalies. There are clear differences between the Baltica, Laurentia and Eastern Avalonia plates in both the magnetic and the gravimetric data. The declination vector image of the gravity field indicates a significant, deep seated lineament just south of the Caledonian Deformation Front, coincident with the Elbe Line. It can be traced from Scotland across the North Sea and into northern Germany. Correlation with deep seismic normal incidence data (the MONA LISA profiles) shows that the lineament coincides with the termination in the lower crust of a band of crust cutting reflections, marking the transition into an area of high reflectivity. A 2D gravity and magnetic model of MONA LISA profile 3 shows evidence of over thrusting of Avalonia onto high density Baltica lower crust over a 150 km wide area. Lower Palaeozoic are found to exist along the entire profile with maximum thickness around 4 km. Near-vertical intrusions are modelled beneath the Central Graben and in the crystalline part of the Mid-North Sea - Ringkoebing Fyn High. By use of local Euler Deconvolution we have modelled depths to magnetic basement in the southern part of the North Sea. An average depth of 7.4 km is estimated for the Norwegian-Danish Basin and 8.0 km for the Horn Graben area. The depth calculations are constrained by power spectral density distributions which show similar results but also indicate the presence of magnetic Rotliegende deposits with depths between 3.0 and 4.2 km. By comparison with the top pre-Zechstein surface, we estimate the thickness of Palaeozoic deposits to be between 3 to 8 km in the Central Graben, 2 to 7 km in the Horn Graben and 3 to 6 km in the southern part of the Norwegian-Danish Basin.
DE: 1219 Local gravity anomalies and crustal structure
DE: 1517 Magnetic anomaly modeling
DE: 8105 Continental margins and sedimentary basins
SC: Tectonophysics [T]
MN: 2003 Fall Meeting