Coaxial Stretching or Lithospheric Simple Shear in the North Sea? Evidence from Deep Seismic Profiling and Subsidence: Chapter 33: North Sea and Barents Shelf

The mechanism of lithospheric extension within the North Sea rift system is a matter of considerable controversy: did the basin form by coaxial stretching of the crust and lithospheric mantle (pure shear) or by lithospheric simple shear? Interpretations of deep seismic-reflection profiling have been used to support lithospheric simple shear, using as evidence basin polarity, crustal reflectors possibly from shear zones, and asymmetry of mantle reflectors. We believe that all this evidence is equivocal and may equally support coaxial stretching. A recently released deep seismic profile across the Central graben is used to illustrate the possible tectonic models and to demonstrate that the deep reflection data are also consistent with a stretching (pure shear) model. Th results of numerical modeling indicate that the lithospheric simple-shear model and other noncoaxial extension models fail to account for the observed distribution of subsidence in the North Sea, which is best explained by coaxial stretching.