Discussion related to Trace Element tutorial in the iolite documentation

furuixin

Bence
Hello, Bence. I found that the Final Th/U ratio output when processing trace elements in zircon is completely different from the ratio calculated using the output values of Final Th and U. What could be the reason for this? Which one is the right

Bence

Hello furuixin

There are two Th/U ratios: Final Th232/U238 and Final U/Th. The first is based on the RM 232Th/238U ratio, and should be very precise. The second is based on the Th and U concentrations in the reference material, and uses the ratio of the two to correct the raw ratios.

The RMs used in U-Pb geochronology (for zircons especially) are typically chosen for their consistent ratios, but their U (and Th) concentrations can vary widely. Here's is just a plot of Plesovice runs, looking at the 91500-normalised U concentrations:

The short answer is that if you're looking for accurate Th/U ratios, use the Final Th232/U238 ratio. The U/Th ratio is provided just a guide.

Note that you must have the 232Th/238U ratio listed in your RM file to calculate Final Th232/U238.

Kind regards,
Bence

furuixin

Bence Thanks，Bence. I still don't quite understand the principle. In the Final result, the ratio of Final U/Th can be derived, but the content of U and Th can also be derived respectively. You mean that the U/Th of this location selected in this zircon should be calculated with the derived U and Th?
for example:

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