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Apatite helium dating

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The basic foundation of the technique is production of where the lambdas are the parental decay constants.

This equation assumes secular equilibrium of U- and Th-series isotopes, though additional information can account for disequilibrium effects in young (He concentration of a sample is a function of both production (as above) and diffusive loss, and can be represented and modeled as a function of time and temperature (e.g., Wolf et al., 1998).

However, once a mineral is sufficiently cool, the He will be retained.

Therefore, when you calculate the (U-Th)/He age of a rock or mineral, you are in effect calculating the time that has elapsed since the system switched from open (hot) to closed (cool) behavior.

At CU we are equipped to measure (U-Th)/He ages on a variety of materials, and are always interested in pursuing new research directions developing new collaborative relationships.

The upward motion of rock masses relative to the Earth's surface has been documented for most of the main mountain belts using thermochronological and petrological techniques.

Most current research using fission tracks is aimed at: a) understanding the evolution of mountain belts; b) determining the source or provenance of sediments; c) studying the thermal evolution of basins; d) determining the age of poorly dated strata; and e) dating and provenance determination of archeological artifacts.

Unlike other isotopic dating methods, the "daughter" in fission track dating is an effect in the crystal rather than a daughter isotope.

He dating is also used in a wide range of other applications, including dating young volcanic rocks, estimating meteorite thermal histories, thermal histories of sedimentary basins, and tracing the effects of wildfire on the earth's surface.

The properties governing diffusive loss are described by Arrhenius laws for thermally activated volume diffusion, with parameters specific to each mineral species, crystal or diffusion domain size, and, in some cases, composition or radiation dosage (e.g., Shuster et al., 2006).

An additional complication to (U-Th)/He ages arises from the fact that He nuclei travel, on average, ~15-20 micrometers away from parent nuclides upon production.

Because this distance is similar (within factor of ~10) as the size of typically dated crystals, an upward correction to the measured He (or downward correction to measured U, Th, and Sm) is required to account for He ejected from them (Farley et al., 1996; Hourigan et al., 2005).

This alpha-ejection correction ranges from about 20-40% of the measured age for zircon or apatite crystals with typical sizes.