Welcome to the HeDiff website presenting the different results and used methodologies.
Dating of geological processes with thermochronology: from the atom to the mountain scale
Understanding the parameters influencing helium diffusion in minerals: contribution to the knowledge of the (U-Th)/He thermochronometer
Quantification of geological processes, like mountain building or sedimentary basin evolution, is based on dating. Thermochronometers are established tools that are widely used to this purpose; however, the physical processes determining a thermochronometric age remain poorly understood. Thus, the apatite (U-Th)/He (AHe) system has quickly became a very popular thermochronometer; however, AHe age interpretation depends on a precise knowledge of He diffusion, that is actually missing. This project groups geologists, mineralogists, theoretical chemists, atomic and material physicists, including two post-doctorate and one PhD fellows, and has for objective to improve significantly our understanding of He diffusion mechanisms in apatite. With innovative analytical and theoretical approaches, we were able to determine and to quantify the parameters influencing helium diffusion, and our conclusions can also been applied to other chronometric systems based on atomic diffusion. The developed methods and results open new perspectives of geochronological research in Earth Science.
Contribution of multi-scales approaches: from quantum calculations to ion beams
The parameters influencing helium diffusion in minerals, such as apatite, were determined by innovative approaches at various scales. From the atomic to macroscopic scale, helium diffusive behavior was characterized for a perfect crystalline system and for crystal possessing defects with the use of quantum calculation, based on Density Functional Theory (DFT). Furthermore, experiments using instruments of material physics such as ion beams were able to determine the impact of the crystalline defects on He diffusion. The method of high-resolution imaging by transmission electron microscopy (TEM) allowed to image crystalline defects. All the results permitted the elaboration of a new He diffusion model in minerals, with the incorporation of changes in mineralogical properties at various scales. Finally, the model is calibrated by the use of different geological cases, where He diffusion occurred during several hundred million years, which allows quantifying the various parameters. This model, incorporated into a data-inversion software, will be used in the future to determine rock thermal histories.