Upper Rhine Graben: role of preexisting structures during rift evolution

[1] The evolution of the Cenozoic Upper Rhine Graben was controlled by a repeatedly changing stress field and the reactivation of a complex set of crustal discontinuities that had come into evidence during Permo-Carboniferous times. A comparison of the spatial and temporal thickness distribution of synrift deposits with preexisting fault patterns permits to infer a sequence of distinct basin subsidence phases that can be related to changes in the ambient stress field. Reactivation of a system of late Palaeozoic fault systems, outlining troughs and highs, controlled the nucleation of initially separated middle and late Eocene basins, the depocenters of which coincided with a preexisting WSW-ENE trend. During Oligocene crustal extension the individual basins coalesced, resulting in the development of the SSW-NNE striking Upper Rhine Graben. During the late Oligocene (Chattian) change in stress field, the Upper Rhine Graben was probably reactivated as a dextral strike-slip system with the central graben segment forming a releasing bend. During the early Miocene (Aquitanian), a major reorientation of the regional stress field is held responsible for the main subsidence phase of the northern parts of the Upper Rhine Graben. This is reflected by a counterclockwise rotation and northeastward shift of the depocenter axis and later by the middle Miocene uplift and erosion of the southern parts of the Upper Rhine Graben. During the Plio-Quaternary, the Upper Rhine Graben was reactivated as a sinistral strike-slip system with the central graben segment forming a restraining bend. INDEX TERMS: 8105 Tectonophysics: Continental margins and sedimentary basins; 8109 Tectonophysics: Continental tectonics--extensional (0905); 8110 Tectonophysics: Continental tectonics--general (0905); 8164 Tectonophysics: Stresses--crust and lithosphere; KEYWORDS: Rhine Graben, evolution, rifting, fault reactivation, stress field, subsidence