Résumé
Fault zones constitute a largely underestimated potential for the worldwide expansion of geothermal power generation. Hydrothermal circulations and convection cells along faults can be complex and localized at the scale of the fault system. Furthermore, thermal anomalies can be hidden without surfac expression: hot spring, gas leak, massive alteration… Low-temperature thermochronology, sensitive for the temperatures targeted for the geothermal exploration (,60- 200°C), appears as a powerful tool to track geothermal anomalies associated to past or long-term or hidden hydrothermal circulations. Recent studies along fault zones in the Eastern Pyrenees reveal that the (U-Th)/He apatite chronometer is sensitive to hydrothermal activity, supported by REE mobility in apatite during fluid-rock interactions. The results demonstrate that apatite can be no longer considered as a closed system and that the effect on AHe dates depends on the intensity of the fluid circulation along the fault. Inside the fault damage zone (DZ) two domains can be distinguished: i) an inner DZ subjected to intense hydrothermal circulations, resulting in AHe rejuvenation or ageing associated to intense mobility in He and REE, and ii) an outer DZ, in which apatites are affected by variable He loss triggering their partial age rejuvenation and associated with REE depletion. Pairing AHe dates with AFT and ZHe dates provides additional constraints for the intensity and extent of the thermal disturbance associated with hydrothermal circulations. This case study opens up new perspectives for the combined use of low-temperature thermochronology and REE analyses for geothermal exploration.