Numerical simulation of rifting in the northern Viking Graben: the mutual effect of modelling parameters

Abstract

Numerous basin modelling studies have been performed on the Viking Graben in the northern North Sea during the past decades in order to understand the driving mechanisms for basin evolution and palaeo temperature estimations. In such modelling, it is important to include lithospheric flexure. The values derived for the lithospheric strength by these studies vary considerably (i.e. up to a factor of 30). In this study, which is based on new interpretation of a regional transect, we show that both the estimated value of the effective elastic thickness and the derived β-profile are dependent on the assumed value of the depth of necking. The use of models that implicitly set the level of necking at a depth of 0 km generally leads to an underestimation of the lithospheric strength, and an overestimation of the thinning factors. In the northern Viking Graben, a necking depth at intermediate crustal levels gives results comparable to the observations. Extension by faulting is modelled to be a significant factor. In conclusion, rifting in the northern Viking Graben can be explained with various models of effective elastic thicknesses (EET) varying from 1 km for a zero necking depth to the depth of the 450 °C isotherm for an intermediate level of necking. It is also shown that the development of the basin during the post-rift phase cannot be explained by pure shear/simple shear extension. Two mechanisms are proposed here to explain the post-rift subsidence pattern, namely intra-plate stress and phase boundary migration. The two extreme models for EET mentioned above (1 km for a zero necking depth to the depth of the 450 °C isotherm for an intermediate level of necking) give very different responses to compressional stress, the latter gives basically no response for realistic intra-plate stress.