Hello Jorge,

Thank you for your contribution. I am aware of how ages are determined using the U-Pb isotopic system in zircon. I think, perhaps, you have misinterpreted my question or my question was misleading as it referred to a question about calculation of concordance/discordance. I refer to the concordia age as defined by Ludwig (1998), not specifically concordant ages and how they are calculated. I take the following quote from the Isoplot 3.75 manual (Ludwig, 2012) which provides a concise description of the corcordia age:

"In addition to the usual 206Pb/238U, 207Pb/235U, 207Pb/206Pb ages, you can use any pair of 206Pb/238U - 207Pb/235U or 238U/206Pb - 207Pb/206Pb ratios to calculate a single “Concordia Age” (Ludwig, 1998). A Concordia Age is the most-probable age for a data-point (or weighted-mean data-point) on a concordia-diagram, where the true location of the data point is assumed to fall precisely on the concordia curve."

Most detrital zircon studies will use the 'usual' ages, particularly utilising 206Pb/238U for ages younger than a certain cutoff (e.g. 1.0 Ga) and 207Pb/206Pb for ages older than the cutoff because the latter age tends to be more precise for older ages. However, using the concordia age removes the necessity for a cutoff.

I refer you to the papers referenced in the question and to:

Spencer et al 2016. Strategies towards statistically robust interpretations of in situ U-Pb zircon geochronology. Geoscience Frontiers 7, 581-589.

Article Strategies towards statistically robust interpretations of i...

The above paper provides a discussion on the cutoff age used to switch from 206/238 ages to 207/206 ages.

My question is aimed at starting a discussion on the pros and cons of the adoption of the concordia age method for detrital zircon studies rather than using the more traditional 206/238 and 207/206 method.

Hi,

I have always used the 206/238 age 1 Ga, although after reading the Zimmermann article it seems logical to use concordia ages instead.

To this end, I wholeheartedly recommend trying this excellent online calculator for geochronology by Pieter Vermeesch, which allows for calculation of concordia ages for many individual spots. The original Excel Isoplot plugin can cause problems with some Excel versions when the add-in is active.

http://pieter-vermeesch.es.ucl.ac.uk/shiny/IsoplotRshiny/R/

Thanks for your answer Roelant. I have used Pieter's R version of Isoplot and would also recommend it as an alternative to the Excel version. I have not tried it for concordia ages though I'd imagine it would be quite laborious to calculate single analysis concordia ages using the Shiny app. However, I'm sure it could be done by writing a short R script and the concordia age routine from the IsoplotR package. Thanks for your contribution!

I recommend Jorge's answer

Best Regards

The new IsotopeR takes care of nearly all variants and gives a more robust and genuine concordia age. Check on this link https://www.ucl.ac.uk/~ucfbpve/isoplotr/ . What I found most interesting is the realistic concordia age estimate from concordant and discordant data from measured 6/8 and 7/5 for younger zircons