ALBERT

Description: The Têt fault is a major crustal-scale fault in the eastern Pyrenees (France) along which 29 hot springs emerge, mainly within the footwall damage zone of the fault. In this study, (U-Th)/He apatite (AHe) thermochronology is used in combination with rare-earth element (REE) analyses in order to investigate the imprint of hydrothermal activity around two main hot spring clusters (Thuès-les-Bains and St Thomas) and between them. The main goal is to better define the geometry and intensity of the recent thermal anomalies along the fault and to compare them with previous results from numerical modelling. This study displays 99 new AHe ages and 63 REE analyses on single apatite grains from samples collected in the hanging wall (18 to 43 Ma) and footwall (8 to 26 Ma) of the Têt fault. In the footwall, the results reveal AHe age resetting and apatite REE depletion due to hydrothermal circulation along the Têt fault damage zone, near the two hot spring clusters, and also in areas lacking present-day geothermal surface manifestation. These age resettings and element depletions are more pronounced around the Thuès-les-Bains hot spring cluster and are spatially restricted to a limited volume of the damage zone. Outside this damage zone, new modelling of thermochronological data specifies the thermal evolution of the massifs. The footwall model suggests the succession of two main phases of cooling: between 30 and 24 Ma and a second one around 10 Ma. In the hanging wall, little evidence of hydrothermal imprint on AHe ages and REE signatures has been found, and thermal modelling records a single cooling phase at 35–30 Ma. Low-temperature thermochronology combined with REE analyses allows us to identify the spatial extent of a recent geothermal perturbation related to hydrothermal flow along a master fault zone in the eastern Pyrenees, opens new perspectives to constrain the geometry and intensity of geothermal fields, and provides new regional constraints on the cooling history of the footwall and hanging-wall massifs.

Description: The Southern Marion Plateau (SMP) represents a vertical stacking of Miocene carbonate platform deposits. Two sites (1196 and 1199) were drilled on top of this plateau, penetrating a 663-m carbonate succession of bioclastic and reefal sedimentary bodies. The study focuses on the least dolomitized 410-m-thick upper part of the succession, which is middle to late Miocene in age. Sedimentological and paleontological studies were conducted at both sites in order to propose a paleoenvironmental model and its evolution through the Miocene age. Six main microfacies of possible environmental significance were defined using statistical multivariate analyses, based on the recognition and point counting of 24 biogenic components. Depositional environment reconstructions are proposed as well as the biosedimentary and the environmental evolution regarding seismic architectures, stratigraphy, biosedimentology, and microfacies analysis. The SMP platform mainly results from a vertical stacking of lens-shaped bodies in homoclinal to distally steepened ramp settings.