zircon radioactive dating

Zircon radioactive dating

A team led by University of Wisconsin geosciences professor John Valley, writing in the February 23, 2014 issue of Nature Geosciences , reports they have pinpointed the location and identity of the individual lead atoms in sub-microscopic sections within one zircon grain from the Jack Hills sandstone north of Perth, Australia. This zircon grain is the width of four human hairs. The research team claims to have confirmed that the lead atoms in that particular crystal’s clock have not moved significantly since the crystal was formed billion years ago.

Uranium–lead dating - Wikipedia

Jim raised the issue of Helium concentrations in Zircon. This is interesting, but it was not discussed at the meeting and I do not know how Justin would respond.

A team led by University of Wisconsin geosciences professor John Valley, writing in the February 23, 2014 issue of Nature Geosciences , reports they have pinpointed the location and identity of the individual lead atoms in sub-microscopic sections within one zircon grain from the Jack Hills sandstone north of Perth, Australia. This zircon grain is the width of four human hairs. The research team claims to have confirmed that the lead atoms in that particular crystal’s clock have not moved significantly since the crystal was formed billion years ago.

Many different radioactive isotopes and techniques are used for dating. All rely on the fact that certain elements (particularly uranium and potassium) contain a number of different isotopes whose half-life is exactly known and therefore the relative concentrations of these isotopes within a rock or mineral can measure the age. For an element to be useful for geochronology (measuring geological time), the isotope must be reasonably abundant and produce daughter isotopes at a good rate.

The existence of two 'parallel' uranium–lead decay routes ( 238 U to 206 Pb and 235 U to 207 Pb) leads to multiple dating techniques within the overall U–Pb system. The term U–Pb dating normally implies the coupled use of both decay schemes in the 'concordia diagram' (see below).

Unfortunately, the breakdown of uranium creates radiation damage in the surrounding crystal, creating avenues for lead to escape. The final point where the sample plots, will be some linear combination of the true concordia age and some final composition where lead diffusion stopped, either the present or some past metamorphic event. If we measure ages for a number of zircons in the sample, and we can now use laser ablation to determine ages for zones within a single crystal, they should plot on a line between those two ages. This sort of plot is a discordia plot, shown above. With a little luck some of the points will plot close to the true age, increasing the precision of the date.


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