Helium trapping in apatite damage:insights from overly dispersed (U-Th-Sm)/He dates.

International audienceOver the past 10 years, the effects of radiationdamage on helium diffusion kinetics werediscovered and led to significant improvements ofthe (U-Th-Sm)/He thermochronomeric system.Nevertheless, helium retention rate and closuretemperature in apatite are still debated, mostlybecause the physical nature of these defects, andtheir ability to trap helium are still unknown.Based on recent experimental analyses andquantum calculation, Gerin et al. (2017) predicthelium diffusion properties in damaged apatite. Inthis contribution, we present a new dataset ofapatite He and AFT ages, from a 300 Ma pluton(French Brittany). Using the new model, wequantify trapping behaviour in terms of energy.The AHe date dispersion for single grain withsimilar eU content may be explained by avariation in the trapping ability. We additionallypropose that damage connect and cluster for highdamage content leading to a decrease of retention.Gerin et al., 2017. Influence of vacancy damage on Hediffusion in apatite, investigated at atomic to mineralogicalscales. Geochim. Cosmochim. Acta. 197, 87-10