A Comparison of the Moho Interpreted From Gravity Data and From Deep Seismic Reflection Data In the Northern North Sea

Abstract

SUMMARY We present the results of gravity modelling of the NSDP-84 deep seismic reflection profiles in the northern North Sea. The Moho depths inferred from forward modelling of marine Bouguer gravity anomalies, from independent inversion of free air gravity anomalies derived from satellite altimetry, and from deep seismic reflection profiling are in good mutual agreement. This agreement suggests that the Moho discontinuity interpreted from seismic reflection data corresponds to a major jump in density and therefore is likely to represent not only the geophysical but also the petrological boundary between the continental crust and the upper mantle. In spite of the significant lateral heterogeneity of the crystalline basement below the northern North Sea area as documented by seismic reflection profiling, the average density contrast between the basement and the upper mantle is interpreted to show rather little variation. This is not true for the deepest part of the Viking Graben where the nature of the lower crust and upper mantle may have been changed by magmatic processes accompanying the graben formation. A relationship between the degree of crustal extension and the volume of magmatic intrusion into the lower crust is tentatively supported by our results.