Apatite helium dating
Further studies of possible variation in diffusion rates between different apatite species are currently being acrried out at Caltech.
An evaluation of low-temperature apatite U-Th/He thermochronometry.
This key observation implies that for any specified thermal history, modelled (U-Th)/He ages can be produced for a particular sample using the measured mean grain size together with single values of the key diffusion parameters E/s.
These values have been used in modelling (U-Th)/He ages for this report.
Assessment of (U-Th)/He thermochronometry: the low temperature history of the San Jacinto mountains, California.
Yellow stones – purplish-pink, which is stronger in long wave; blue stones – blue to light-blue in both long and short wave; green stones – greenish-yellow, which is stronger in long wave; violet stones – greenish-yellow in long wave, light-purple in short wave.
Because of the greater diffusive loss expected from smaller grains compared to larger grains, the helium closure temperatures in apatite will also vary with grain radius.
The overall variation in closure temperature for samples with grain radii of 50-150 microns is predicted to be only 5C (Farley, 2000).
Their results also suggest that, in general, helium diffusion systematics derived from laboratory measurements can be extrapolated to geological conditions with confidence, although the exact details details remain to be quantitatively assessed.
Modeling of the temperature sensitivity of the apatite (U-Th)/He thermochronometer.
Helium diffusion and low-temperature thermochronometry of apatite.
In principle, therefore, this technique provides a useful supplement to the information provided by AFTA.
represents the alpha-decay constants for the respective isotopes and t is the time over which He has accumulated.