Hi there,

This is going to depend exactly on the type of age calculated. Typical ages quoted for zircon would be

1) a mean age

2) an intercept age

3) a concordia age

In the case of a mean age it should be a weighted mean of your age of interest (usually 207/206 for old zircon quoted in your question). Weighted mean ages are pretty easy maths.

Intercept ages are used when you have 2 significant ages (sometimes more but 2 is a simple case) with discordant zircon spread between them. In this case it is a similar calculation but based on your tie line, not a single 'axis'

Concordia ages are calculated based on 'matching age sets' e.g U/Pb-Pb/Pb or U/Pb-U/Pb. These ages are fairly heavy maths to do by hand!

If you are doing lots of this work I would recommend reading the manual for Squid2 (which is a free download) produced by Ken Ludwig at the Berkeley Geochron Centre (download link below). The Squid program processes SHRIMP U-Pb data files and this manual has plenty of info on how it calculates ages.

http://sourceforge.net/projects/squid2/?source=directory

There is also a GCA paper by Ken Ludwig that goes through lots of the maths in detail for concordia ages, and associated errors that need to be included, titled "On the Treatment of Concordant Uranium-Lead Ages". link below

http://www.sciencedirect.com/science/article/pii/S0016703798000593

That should get you started!

Cheers

Rich

I suggest you to start reading some geochemistry books like White, Faure & Mensing, Dicking, where the authors make excellent reviews about geochronology and everything that is necessary to calculate an age. Below, there are two suggestions.

White, W. M. Geochemistry. - Chapter 8: Radiogenic Isotope Geochemistry

Faure & Mensing. Isotopes - Principles and Applications. 2005 - Principles of Atomic Physics (Geochronometry) and Part II Radiogenic Isotope Geochronometers

Thanks for the suggestion.

Many (jn fact the majority when dealing with in-situ methods) of papers, do not state what the stated uncertainty (not error) is based on. In particular, whether it comprises a component relating to systematic uncertainties. These can include decay constants, uncertainty in the reference material ratios, common-lead composition, and long-term variance of the lab. The Laser Ablation working group has produced a workflow for how these uncertainties should be dealt with. The publication explaining this is currently near completion. So do look out for it!

http://www.plasmage.org/recommendations

Thanks Nick, this is really useful.