Abstract
Abstract. The influence of strain distribution inheritance within fault systems on repeated fault reactivation is far less understood than the process of repeated fault reactivation itself. By evaluating cross sections through a new 3D geological model, we demonstrate contrasts in strain distribution between different fault segments of the same fault system during its reverse reactivation and subsequent normal reactivation. The study object is the Roer Valley graben (RVG), a middle Mesozoic rift basin in western Europe that is bounded by large border fault systems. These border fault systems were reversely reactivated under Late Cretaceous compression (inversion) and reactivated as normal faults under Cenozoic extension. A careful evaluation of the new geological model of the western RVG border fault system – the Feldbiss fault system (FFS) – reveals the presence of two structural domains in the FFS with distinctly different strain distributions during both Late Cretaceous compression and Cenozoic extension. A southern domain is characterized by narrow (<3 km) localized faulting, while the northern is characterized by wide (>10 km) distributed faulting. The total normal and reverse throws in the two domains of the FFS were estimated to be similar during both tectonic phases. This shows that each domain accommodated a similar amount of compressional and extensional deformation but persistently distributed it differently. The faults in both structural domains of the FFS strike NW–SE, but the change in geometry between them takes place across the oblique WNW–ESE striking Grote Brogel fault. Also in other parts of the Roer Valley graben, WNW–ESE-striking faults are associated with major geometrical changes (left-stepping patterns) in its border fault system. At the contact between both structural domains, a major NNE–SSW-striking latest Carboniferous strike-slip fault is present, referred to as the Gruitrode Lineament. Across another latest Carboniferous strike-slip fault zone (Donderslag Lineament) nearby, changes in the geometry of Mesozoic fault populations were also noted. These observations demonstrate that Late Cretaceous and Cenozoic inherited changes in fault geometries as well as strain distributions were likely caused by the presence of pre-existing lineaments in the basement.
Highlights
Rift basins are typically bounded by large fault systems
Based on stratigraphic maps extracted from the new 3D geological model of Flanders (G3Dv3 model; Deckers et al, 2019), it is shown that, in agreement with former studies (Rossa, 1986; Demyttenaere and Laga, 1988; Demyttenaere, 1989; Langenaeker, 2000), the Feldbiss fault system (FFS) was highly active during both Late Cretaceous contraction and Cenozoic extension
We identified two of those structural domains in the Belgian sector of the FFS, which existed during both Late Cretaceous contraction and Cenozoic extension:
Summary
Rift basins are typically bounded by large fault systems These border fault systems are generally segmented along strike. As they represent zones of pre-existing weaknesses, the large border fault systems are prone to reactivation under either extension or compression. One of the ideal areas to study these effects is at the border fault systems of the Roer Valley graben (RVG). These systems developed in the middle Mesozoic and were reversely reactivated under Late Cretaceous contraction and experienced normal reactivation again under Cenozoic extension (Demyttenaere, 1989; Geluk et al, 1994).
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