Helium trapping in apatite damage: insights from overly dispersed (U-Th- Sm)/He dates.
Résumé
Over the past 10 years, the effects of radiation
damage on helium diffusion kinetics were
discovered and led to significant improvements of
the (U-Th-Sm)/He thermochronomeric system.
Nevertheless, helium retention rate and closure
temperature in apatite are still debated, mostly
because the physical nature of these defects, and
their ability to trap helium are still unknown.
Based on recent experimental analyses and
quantum calculation, Gerin et al. (2017) predict
helium diffusion properties in damaged apatite. In
this contribution, we present a new dataset of
apatite He and AFT ages, from a 300 Ma pluton
(French Brittany). Using the new model, we
quantify trapping behaviour in terms of energy.
The AHe date dispersion for single grain with
similar eU content may be explained by a
variation in the trapping ability. We additionally
propose that damage connect and cluster for high
damage content leading to a decrease of retention.
Gerin et al., 2017. Influence of vacancy damage on He
diffusion in apatite, investigated at atomic to mineralogical
scales. Geochim. Cosmochim. Acta. 197, 87-103