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The U-Th-Pb method is used to study igneous and metamorphic processes affecting U-Th-bearing minerals such as zircon and apatite, whereas the U-Th-He method is used to study low temperature processes occurring near the Earth’s surface. (1987), the U-Th-He method has found a large number of applications in tectonics and geomorphology (Reiners and Shuster, 2009).
A fundamental driving force behind these applications have been technological advances in mass spectrometry and micro-analytical technology, which have led to a steady reduction of sample size while increasing sample throughput at the same time.
Because the U-Th-He age equation is scale invariant, it does not matter if a mineral’s U, Th, and He contents are expressed as atomic abundances or concentrations.
They can even be renormalised to unity and plotted on a ternary diagram (Vermeesch, 2010).
So far, this method has been successfully applied to monazite (Boyce et al., 2006, 2009), zircon (Tripathy et al., 2010; van Soest et al., 2008), and apatite (van Soest et al., 2008).
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 should be a large gem-quality crystal, ensuring relatively uniform ablation behaviour, while saving the user the trouble of polishing and mounting large numbers of crystals in Indium.
Second, it should lack major compositional zoning and have relatively uniform U and Th concentrations.
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).Tags: Adult Dating, affair dating, sex dating