The Rôle of Faults on Hydrothermal Circulations in the Têt Valley (Eastern Pyrénées)

Hot springs in continental systems often localize near major faults. Faults may act as drains or barrier for hydrothermal circulation, depending on their core zone constitution and permeability, and the fracture density, opening, and connectivity in their damage zone. The interplay between these processes is still unknown and remains to be studied. The french eastern Pyrénées hot springs are an ideal case to understand how faults controls hydrothermal circulations and hot springs distributions. They align with the brittle normal Têt fault. The basement rocks affected are composed of highly fractured, foliated, gneisses, granites, and metasediments. Photo-interpretation and field work reveal that hot springs discharge in the footwall, along a ductile fault (CMNC), or at the Têt fault linkages with subsidiary brittle faults. Because of the topographic gradient induced by the fault offset, fractures and foliation drive meteoric water toward the deep reservoir where it acquires temperature. Hot waters then use damage zone fracture to rise up, restricted in the footwall because of the presence of main drains in the damage zone and poorly permeable fault rocks in the core zone. Well oriented in-situ stress or seismic activity, could help to maintain the fractures opening, which are generally cemented by zeolites.