I did experiment on U-Pb age dating by LA-ICP-MS, and got MSWD -9, or even more then 9, in two samples, can any one please tell me why MSWD is too high, why it happens during this analysis.
Regards Mastoi
MSWD is a Mean Square Weighted Deviation, which tells the deviation among age data is large if the value is large. Two possibilities,
First, either the results are not analytically good. That can be confirmed by internal or external standards used during the LA-ICP-MS analysis. If the results from standards are accurate, your age data should be accurate too.
Second, the analysis might have been done on mixed zones in zircon, and when averaging different zones together, the deviation should be relatively large.
You can see that by looking carefully the CL images if you have, they may give some clue.
Apart from the possibilities that Hafiz gave, it could also be that there is more than one population of zircon (or whatever other mineral you may have dated); or that some of the zircons have lost Pb; or that you have underestimated the uncertainty of the individual analyses that you have used to calculate the age. Is this MSWD for concordancy, or for an upper- or lower-intercept age? Perhaps you should give the diagram on which you base your statement, and we can say something more.
Thank you very much such a nice suggestion from Dr. Hafiz and Dr. Malina Elburg, i will recheck data and follow your instructions Dr.Elburg, if i get satisfied from sorted results then ok , or i contact you by email. Thanks and Regards Mastoi
What is the MSWD of the standard grains? Check that to consider instrumental instability as a factor!
Well thanks for respond dear amitava, in some samples it was error calculated so we did that same experiment again and this time got readonable results.
Regards
Dr.Mastoi
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