Pre-Neogene controls on present-day fault activity in the West Netherlands Basin and Roer Valley Rift System (southern Netherlands): role of variations in fault orientation in a uniform low-stress regime
Résumé
The West Netherlands Basin (WNB) and the neighbouring Roer Valley Rift System (RVRS) form the most prominent tectonic features of the onshore Netherlands. The two basins have a common tectonic origin and similar Mesozoic evolution, their Neogene–Quaternary evolution, however, is markedly different. While the WNB is tectonically/seismically inactive and is characterised by uniform Neogene–Quaternary subsidence, in the RVRS fault controlled intra-plate deformation has taken place since Late Oligocene times with pronounced seismic activity. Considering the present-day NE–SW regional extension as well as the similar basin orientation and Mesozoic evolutions one would not expect strikingly different neotectonic activity in the two basins. Detailed analysis of Mesozoic, Tertiary and Quaternary fault patterns revealed that (1) the Palaeozoic–Mesozoic tectonic fabric has great influence on the Cenozoic deformation style of the basin system; (2) present-day faulting in the RVRS is related to the reactivation of pre-existing faults and (3) the Mesozoic fault pattern is slightly different in the two basins. Using a novel technique (three-dimensional (3-D) slip tendency analysis) we aim to determine whether these differences in fault orientation are substantial enough to produce significantly different resolved stresses along the faults. This modelling not only tests a common geological phenomena but indirectly also delivers important constraints regarding the origin of faulting in the study area. During the analysis 3-D geometric models of 84 mapped faults were investigated. The results of this recently developed modelling technique reveal that the faults in both basins should behave similarly under the condition of a laterally homogeneous regional stress field, which is in disagreement with the present-day tectonic activity of the region. On the other hand the modelling also reveals that the predicted tendency of slip is very sensitive to the ratio of the minimum horizontal and the vertical stress (S). As an explanation for the pronounced fault activity in the RVRS and the tectonic quietness of the WNB it is proposed that either the regional extension in the WNB is ‘‘weaker’’ (in term of higher S ratio) than that in the RVRS or the slip thresholds in the two basins are different. The study emphasised that differentiation in the tectonic evolution has already started in the Tertiary, therefore, it is reasonable to assume that the different tectonic stress field and/or slip threshold between the two areas is directly related to the origin of the Cenozoic rifting in the RVRS. Several hypotheses are discussed to account for these two possibilities, taking into account the lithospheric structure and the Cenozoic tectonic evolution of the two basins as well as surrounding areas.
Domaines
TectoniqueOrigine | Fichiers produits par l'(les) auteur(s) |
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