Faults act as conduits for large-scale fluid movements, often hosting multiple circulation events within their brecciated structures.
In the Alps, particularly along the Penninic Frontal Thrust within the ‘Briançonnais Zone’, a mineral assemblage of calcite and hematite has been observed in the breccias of the High-Durance normal Fault System (HDFS). Recent geological investigations have utilized a multidisciplinary approach, including petrological analysis, geochemical examination of calcite (involving stable isotopes and clumped isotopes analysis), and U-Th-Pb dating.
U-Pb dating on calcite provided dates ranging from 5.3 to 2.3 Ma and Hematite (U-Th)/He dating from 13.3 to 0.2 Ma. All ages indicates the onset of transtensional fault activation and the transition from the previous compressional tectonic regime in the Middle Miocene with a westward migration of the extension. The onset of the HDFS extensional regime thus appears to be contemporaneous with the development of the fold and thrust belt of the western Alpine foreland.
Two isotopic signatures (Δ47) of the calcites suggest an open fluid system with (1) crystallization temperatures around 130°C related to deep fluids and (2) a meteoric fluid signature (36°C) associated to a 1900m precipitation altitude, indicating that similar altitudes were present around 2 My ago. This coincides with the transition from a Mediterranean climate to a colder, glacier-dominated climate, leading to valley formation during this period.