Apatite (U-Th)/He Thermochronology Data Interpretation in Fold and Thrust Belt - New Insights from Physical Point of View

The apatite (U–Th)/He (AHe) system has rapidly become a very popular thermochronometer to constrain burial and exhumation phases in a variety of geological contexts, including fold and thrust belt. In this particular case, detrital apatite crystals come from different sources and are characterized by different pre-deposit ages and grain chemistry. However the actual He diffusion models are not well constrained and do not fully explain the mechanism of He retention. This is particularly true for detrital apatite crystals and AHe age interpretation can be tricky. In order to have a deeper insight on this issue, multidisciplinary studies on apatite combining physical studies were performed. We propose new He diffusion coefficient, so closure temperature and a physical He diffusion model. We will propose a new way of interpreting AHe datasets on fold and thrust belt samples more particularly, because of their own apatite characteristics. Two examples from Peruvian Subandean zone and south Pyrenean foreland will be given. We will show how a better interpretation of He diffusivity will improve significantly AHe data and thermal histories obtained by data inversion.