Fluid-rock interaction control on fault reactivation: A review of the Montmell-Vallès Fault System, central Catalan Coastal Ranges (NE Iberia)

Abstract

Structural inheritance is a key factor controlling the tectonic evolution of the central Catalan Coastal Ranges. Up to two periods of tectonic inversion (one positive during the Paleogene and the other negative during the Neogene) affected a previously well-developed Mesozoic extensional basin system and characterized the Cenozoic evolution of the area. In this scenario, tectonic fault inversion is often observed along the Montmell-Vallès Fault System. Fault reactivation shows differences along strike from NE to SW and appears decoupled from surface to depth due to its kinked-planar geometry and the change of fault dip from >60° to 30° in depth. The ability of the Mesozoic faults to be reactivated appears also influenced by changes in the mechanical properties of the inherited fault zone. Whereas the deeper and less dipping panels of the major faults are reactivated in the entire zone (contractional during the Paleogene and extensional during the late Oligocene-Neogene), the upper and highly dipping parts of the faults only show local reactivations. The observations indicate that fault dip, the indirect role of hosting lithologies (granites and siliciclastic metasediments versus carbonate rocks) on fault rocks, the indirect role of mineral precipitation and cementation product of fluid circulation, and the direct role of the mechanical properties of the resulting fault rocks (gouge versus cemented breccias) significantly control the fault reactivation. Upper crust low angle fault segments are easily reactivated during contractional deformation but not during the extensional one. Conversely, the segments with a high-angle dip are more easily reactivated during the extensional deformation but not during the contractional one. In the study area, this resulted in the formation of footwall short-cuts developed during the Paleogene compression and extensional short-cuts occurred during the Neogene extension. On the other hand, reactivation is effective in areas where granites and siliciclastic metasediments characterize the host-rock, and non-cohesive fault gouge forms the pre-existent fault core. Instead, fault reactivation appears restricted or even prevented where the host-rock includes thick carbonate successions, and the pre-existent damage zone is formed by highly cemented and cohesive breccias.