2025/05/29 by Gaétan Milesi, Philippe Münch, Delphine Charpentier +7 · 1 voice
Earth and Planetary Sciences · #earthquake and tectonic studies #Geological and Geophysical Studies Worldwide #Geological and Geochemical Analysis
paper · doi:10.1016/j.jsg.2025.105465
openalex publication_date 2025/05/29 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/22
: In orogenic settings, fault networks accommodate crustal deformation during the evolution of mountain ranges. Fault zones exhibit multiphase ductile and brittle activity, complicating their interpretation. Dating deformation in orogenic basement remains a challenge. In this study, we conducted structural and microstructural observations, coupled with 40 Ar/ 39 Ar dating on encapsulated mineral fractions and chlorite thermometry, on major fault zones in the Eastern Pyrenees. To overcome the presence of K-feldspar within fault gouge, a major issue for fault gouge argon dating, we present a method to estimate the contribution of two mixed K-rich phases from 40 Ar/ 39 Ar step heating. This method provides limit or maximum age for the deformation recorded by fault gouges in which illite polytypes are mixed with K-feldspar. Our results reveal a ductile-to-brittle transition between 40-35 Ma (Priabonian-Bartonian), characterized by 2 M 1 muscovite and evidence of strike-slip movement along the Py NE-SW fault and NW-SE secondary faults. The Py fault gouge contains muscovite formed at temperatures exceeding 200-250°C. In the Têt NE-SW fault gouge, the coexistence of 2 M 1 and 1 M illite polytypes suggests late-stage crystallization of 1 M illite at 22.1 ± 1.4 Ma, at temperatures between 100-150°C, as determined by chlorite thermometry. These findings confirm significant normal faulting activity on the Têt fault during the Oligo-Miocene, consistent with published low-temperature thermochronology data indicating early exhumation of the Canigou massif relative to the Carança massif, facilitated by normal displacement along the Py fault, and a later exhumation of both massifs in relation to the Têt normal fault activity.