The zircon grains I got from my peralkaline granites are irregular and stubby with 1:1 predominant aspect ratio from length 60 - 130 um and width 45 - 80 um to give a sub-angular outline (bipyramidal). It also appear cloudy and brown in transmitted light. More so, there are no oscillatory growth zone discernible on the CL image (see attached images).
Thank you Leonid Shumlyanskyy . Yes, the contents of U from my trace elements is a bit anomalous. The granite is albite arfvedsonite and it contains Nb rich pyrochlore.
Yes, it looks like Leonid Shumlyanskyy is absolutely right, and your zircons are metamict. This is not unusual for zircons from high-U granites, even if they are not that old. If you are interested in finding the age for your granites, you may be better off looking for U-bearing phosphates rather than trying to data these zircons. They won't give you a decent age.
I also agree that these zircons are probably metamict. You can test with a Raman microprobe their degree of crystallinity.
Have you their uranium content ?
Michel Cuney yes sir.
U = range from 119 to 663
Pb = range from 3 to 59
The higher values of U are largely in the core and there is inverse proportional relationship between U and Pb (r = -0.68)
OK thank you sirs Leonid Shumlyanskyy and Michel Cuney . The aluminous (biotite granite) in contact with the peralkaline granite has higher U contents. I probed 30 zircon grains from 3 biotite granites and got U (ppm) ranges:
Dtm = 4429.5 - 241.8
St4 = 6111.75 - 1904.99
Rp2 = 7210.66 - 214.87
Are you sure that this is zircon? Do you have EDS spectra showing a zirconium peak?
Leonid A. Neymark No, I do not have EDS spectra but the chemistry results with a calibrated quadruple-ICP-MS shows ZrO2 is the most abundant major content >66 wt%.
What about Na content in your analysis, can you read about eudialite group minerals,
Thanks Nasser Elagami . They are recrystallized zircon grains with high soda contents. Hence, I believe it is elpidites. However, an on-going effort is on to find out if there are more than one population of in the albitized sodic amphibole granites.
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