What is helium dating

Second, it should lack major compositional zoning and have relatively uniform U and Th concentrations.Third, it must not show any significant core-to-rim depletion in helium content due to diffusive loss during cooling.In-situ U-Th-He geochronology by laser ablation potentially offers the following advantages over conventional U-Th-He dating by whole grain degassing and dissolution.First, it dramatically increases sample throughput. Measuring the U and Th content of zircon by isotope dilution requires dissolution in hydrofluoric acid at high temperature and pressure using a Parr bomb for up to 48 hours.From 1987 until 2000, helium was measured by bulk degassing of multi-grain aliquots in a resistance furnace, and measuring the U-Th content on either the same or a different aliquot by XRF or TIMS (Zeitler et al., 1987; Lippolt et al., 1994; Wolf et al., 1996).In 2000, a method was developed to degas individual mineral grains by means of laser-heating in Pt or Nb ‘micro-furnaces’, followed by acid dissolution and U-Th analysis by isotope dilution in an ICP-MS (House et al., 2000).

This can be done without the need to use a separate reference material, if a U-Th-He age standard is used that is concordant in its It is important to note that the Th/U ratio only needs to be determined for the standard.They can even be renormalised to unity and plotted on a ternary diagram (Vermeesch, 2010).To calculate a helium age, it is not necessary to know the absolute concentrations of U, Th, and He.It suffices that two elemental ratios are known, such as U/He and Th/He, or U/Th and U/He.This insight forms the basis of the simplified method, which does not require knowledge of any absolute abundances or concentrations, but instead uses the raw mass spectrometer measurements.

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