Polyphased brittle deformation around a crustal fault: a multi-scale approach based on remote sensing and field data on the mountains surrounding the Têt hydrothermal system (Eastern Pyrénées, France)

Audrey Taillefer (1) , Gaétan Milesi (1) , Roger Soliva (1) , Loïs Monnier (1) , Pauline Delorme (2) , Laurent Guillou-Frottier (3) , Elisabeth Le Goff (3)

1 Géosciences Montpellier
2 School of Geography and Environmental Science of Southampton
3 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)

Studying hydrothermal systems in basement environments requires knowledge of fault and fracture network distributions. This study addresses this through multi-scale structural analysis of the Têt fault and its surrounding fracture systems (Eastern Pyrénées) using remote sensing and field data. This study aims to achieve this through: 1) precisely mapping and describing the brittle fault network, 2) analysing the distribution of lineaments and outcrop-scale fractures related to these faults, 3) making comparisons to fault-kinematic evidence combined in a new regional review, 4) examining the relations between fractures features and lithology, 5) applying statistical analysis to highlight relations between different scales of deformation. The complex fault network is inherited from consecutive tectonic stages (Hercynian, Pyrenean compression, Neogene extension) and has been reactivated since the middle-Miocene. NE–SW secondary faults are abundant at the regional scale, even away from the Têt fault. Major NW–SE faults are constituted by 10s-m wide brittle core zones, and NW–SE secondary faults are concentrated around the Têt fault, attesting that they had formed at shallow crust levels after the Oligo-Miocene extension. N–S fractures, formed during Pyrenean compression, are part of the background fracturing and are scatteredthroughout the study area. Intersections of fault and fracture networks provide efficient permeable pathways for meteoric and hydrothermal fluids. Finally, a dislocation model reveals a lithological control on fracture apertures in crystalline rocks, which appears more preservedat depth than in metasediments. All of these elements are integrated in a global model of the hydrothermal system establishment in accordance with the faulting sequence, with the damage distribution and with the lithology. This distributed fault system could represent the surface expression of the crustal thinning revealed by recent geophysical data. The realized identification of the lithological and structural characteristics of the surrounding mountains, allowing hydrothermal circulation to establish itself, provides a better understanding of the orogenic-belt related hydrothermal systems necessary to the geothermal exploration.

Domaines: Géologie appliquée

Audrey Taillefer, Gaétan Milesi, Roger Soliva, Loïs Monnier, Pauline Delorme, et al.. Polyphased brittle deformation around a crustal fault: a multi-scale approach based on remote sensing and field data on the mountains surrounding the Têt hydrothermal system (Eastern Pyrénées, France). Tectonophysics, 2021, ⟨10.1016/j.tecto.2020.228710⟩. ⟨hal-03170385⟩