Metropolitan France and a focus on Chaudes-Aigues (French Massif Central) The occurrence of high-temperature thermal springs in amagmatic context raises a fundamental question: why does a hot spring emerge at a given location? This study tries to fix this issue through a multi-scale approach combining statistical and physical analyses. First, a large-scale statistical investigation is conducted at the scale of metropolitan France, based on a database of more than 360 thermal springs. Different parameters are examined to identify a dominant controlling factor governing the spatial distribution and temperature of thermal springs. A second approach based on thermo-hydraulic modelling is developed and applied to the hydrothermal system of Chaudes-Aigues, hosting the hottest spring in Europe. This statistical approach suggests that hot spring formation results from the complex interaction of these factors. Several model configurations are tested integrating topography and a deep reservoir reaching 190°C identified by geochemical studies. Only models including both elements successfully reproduce all field and geochemical criteria. Models also constrain the infiltration area along a major fault system and indicate long residence times (50 – 200 kyr). These results highlight the key role of coupled structural control, topography and deep fluid circulation in the genesis of thermal springs. Together, this two-step study provides new insights of the thermal spring origin in amagmatic context. • Thermal spring distribution in France results from multiple interacting factors. • Spring temperature may be controlled by fault density with optimal permeability. • At Chaudes-Aigues, fault permeability dominates over topographic effects. • Numerical reproduction of spring features (location, temperature and flow rates).
Penhoët et al. (Sat,) studied this question.