Backward modeling of the rifting kinematics in the Upper Rhine Graben: insights from an elastic-perfect contact law on the restoration of a multi-bloc domain

Abstract

This paper addresses the problem of volume restoration for 3-D sedimentary basin kinematic deformation. The primary purpose is methodological and concerns the use of contact mechanics with the finite element method, in order to deform a geological multi-bloc domain. This approach is applied to backward model the later stage of rifting of a segment of the southern Upper Rhine Graben (France-Germany border). Preliminary results from our modeling demonstrate the ability of the method not only to handle complex geometries, but also to successfully perform retro-deformation of a complex geological domain. In addition, they provide or confirm crucial information on the rifting evolution and tectonic features of this segment of the Upper Rhine Graben, such as the distribution of deformation, the asymmetry of the graben and a significant left-lateral strike-slip component of displacement.

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“…The backward model is in good agreement with the results of previous studies (Behrmann et al, 2003;Cornu and Bertrand, 2005b;Bertrand et al, 2005) which show that (1) the maximum deformation occurs along the border faults, and (2) maximum subsidence is centred on the south-western part of the graben. In addition, the direction and magnitude of observed strike-slip values are compatible with those of a simple 4-block model (Cornu and Bertrand, 2005b). Although these lateral motions are mainly a function of fault orientation, an oblique extension component is required for the development of the observed fault pattern.…”

“…Displacement components along the 3 axes provide information on rifting processes in the URG. As previously suggested by forward modelling and Cornu and Bertrand (2005b), the majority of deformation is initially accommodated along the border faults (Fig. 23d,e for heave and 23f for throw) with only a minor part being distributed within the graben itself.…”

“…Despite strict boundary conditions and a purely orthogonal rifting scenario, components of strike-slip motion have been identified along all faults. Strikeslip components range from a few tens to about 100 m, as in the previous simple backward model (Cornu and Bertrand, 2005b). In case of partly oblique rifting, it is likely, that the URG accommodated a significant component of strike-slip motion.…”

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“…However, in case of oblique extension, deformation is not necessarily restricted to the border faults: a narrow band of high strain and brittle behaviour develops in the centre of the graben along its axis (Fig. 36) (Cornu and Bertrand, 2005a). This zone is the likely location of subsequent faults that develop during oblique rifting.…”