Finite element modelling of a continental rift structure (Rhinegraben) with a large-deformations algorithm

Abstract

The formation of continental rifts with small extension values can be simulated over several tens of millions of years by means of a finite element program able to handle large deformations. As an example an attempt has been made to model the formation of the northern and southern Rhinegraben over the past 40 m.y. Deviatoric extensional stresses of 25–40 MPa were required and, to model the Moho uplift, mass anomalies in the lower lithosphere had to be invoked with density contrasts of −0.15 and −0.30 g/ cm 3 for the northern and southern Rhinegraben respectively. Trial models without a mass anomaly in the lower lithosphere resulted in crustal thickening beneath the graben and not crustal thinning. In the northern Rhinegraben the rifting is more passive and uniform and model subsidence values of 4000 m were obtained together with model shoulder and Moho uplifts of 800 m and 1500 m respectively. In the southern Rhinegraben the rifting is more active and episodic and, in fact, between 13 and 10 m.y. ago the model graben floor was uplifted in order to simulate the observed graben floor uplift at around 10 m.y. ago. Model subsidence values of 2000 m were obtained while the model shoulder and Moho uplifts were 1900 m and 7000 m respectively in good agreement with the observed values.