Impact of polyphase tectonic on fractured basement reservoir: Insight into the basin-basement interface from the Villé Basin (Vosges, France)

Fluid circulation at basin–basement interfaces in rift systems is primarily controlled by brittle fault networks evolution and major interfaces. In the Upper Rhine Graben (Vosges, France), fractured crystalline basement rocks host major geothermal reservoirs, although the relationship between present-day fluid circulation and inherited, relict hydrothermal pathways remains debated. This study investigates the structural and hydrothermal evolution of the Villé Basin (Vosges Massif, France), located on the western shoulder of the Upper Rhine Graben, and provides a natural analogue for fractured basement reservoirs. The Villé Basin exposes the unconformity between the granitic basement and Stephanian sedimentary cover, allowing direct observations of faulted basement–cover interfaces. An integrated approach combining structural field analysis, petro-mineralogical characterization, and geochronological dating was applied to constrain fault activity and fluid circulation episodes. Two main brittle fault systems are identified: (i) An E–W-oriented fault network is pervasive at the basin scale and connects the basement to the sedimentary cover. These normal faults with metric vertical displacements are associated with hematite mineralization, and localized late barite mineralization event, indicating several hydrothermal circulations. Rb–Sr ages on muscovite and biotite suggest fault activity during Carboniferous–Permian times associated with N020°E extensional constrains. (ii) A later N–S-oriented fault network is localized along major basin-bounding faults associated to kilometric vertical displacement related to the formation of the Rhine graben. U–Pb dating of newly-formed anatase (TiO2) yields Jurassic-Cretaceous ages (142 ± 66 Ma) questioning the activation of brittle N-S faults, low-temperature clay assemblages (kaolinite, illite/smectite, calcite) indicate late fluid circulation during late stages of URG evolution. These results demonstrate that the structural architecture of fractured basement reservoirs is controlled by evolution of fault systems and their episodic (re-)activation. The Villé Basin highlights the importance of structural control when interpreting geochronological data and provides key insights into fluid flow processes relevant to better understand complex geothermal systems of the Upper Rhine Graben.