Hydrothermal Activity along a Crustal Fault in the Pyrenees (France) Evidenced by Thermochronology and REE Analyses

Abstract:

The Pyrenees mountain range shows evidence of hydrothermal activity, among which the Têt fault (eastern Pyrenees) localizes 29 hot springs, mostly in the fault damage zone footwall. In this study, low temperature thermochronology (AHe, AFT and ZHe) combined with apatite REE analyses of the dated grains are used to better define the influence of the thermal anomaly along the fault and the isotherm distribution at depth.

The results demonstrate a correlation between AHe age resetting and apatite REE depletion in the footwall damage zone of the Têt fault. The intensity of both processes is more pronounced around the hottest spring cluster and spatially restricted to the fault damage zone. The location of thermal anomalies is essentially controlled by the presence of high reliefs adjacent to the fault and of secondary faults intersecting the Têt fault. AFT and ZHe ages obtained within the fault damage zone are not affected by hydrothermal resetting and are consistent with all the thermochronological data recorded in the footwall and hanging wall of the Têt fault. Together with the data obtained outside the damage zone, the thermochronological results are used to recover the regional thermal history of the eastern Pyrenees and to propose a new thermo-kinematic history based on QTQt and Pecube modeling.

This work shows that even in the absence of surface hydrothermal activity, AHe ages in fault zone can be affected by hydrothermal perturbation. The coupling of AHe ages and apatite REE analyses can highlight thermochronometers impacted by hot fluid circulation and represent an efficient criterion of sample selection for the construction of a regional thermal history. This original application of the coupling of thermochronology and REE analyses opens new perspectives for geothermal exploration in orogenic contexts.