Modeling of the temperature sensitivity of the apatite (U-Th)/He thermochronometer. Helium diffusion and low-temperature thermochronometry of apatite. More recently, measurements of (U-Th)/He ages in samples from hydrocarbon exploration boreholes in the Otway Basin of S. Australia (House et al., 1999) have confirmed this general pattern of behaviour. 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.
Several studies suggest that the composition of the apatite does not appear to affect the sensitivity of the He closure temperature (Wolf et al., 1996; House et al., 1999), in contrast to the effect of Cl contents on AFTA annealing kinetics. Journal of Geophysical Research, 105 (B2), 2903-2914. However, effects related to grain size may be significant in the interpretation of apatites from sediments which have been heated to paleotemperatures within the He PRZ, as grains of different radii will give different ages for a particular thermal history. The effects of long alpha-stopping distances on (U-Th)/He ages. While this has yet to be demonstrated in natural samples, this holds considerable promise for obtaining more precise thermal history control in sedimentary basins. Ken Farley of Caltech, based on the systematics presented in Farley (2000) and references therein, allows modelling of the (U-Th)/He age expected from any inputted thermal history, in grains of any specified radius. Helium is produced within apatite grains as a result of alpha decay from uranium and thorium isotopes, present as impurities at ppm levels. (1994), this process formed the basis of the first attempts at geochronology (Rutherford, 1907a). Rutherford, 1907b) that at least a fraction of radiogenic Helium was lost from the host crystal lattice, and with the advent of apparently more reliable methods of geochronology (e.g. K-Ar, Rb-Sr, U-Pb), interest in the Helium systematics of minerals waned.