I have a problem when I use UPb_commonapproach to reduce apatite U-Pb data. I used Madagascar apatite as the primary standard for downhole fractionation correction and NIST612 to do the 207Pb/206Pb correction. Everything looked normal, but I got Madagascar age of ~970 Ma, which is much older than its true age of 474 Ma. I have tried to use “observed slope” to do the 207Pb/206Pb correction. A somewhat younger age was returned (for Madagascar), but it was still not quite right.
I have also tried with VisualAge_UcomPbine. No problem with this DRS.
Does anyone know why UPb_commonapproach would return a wrong age for the primary standard?
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