Actually, can we perform the in-situ Pb isotope system (by using MC-LA-ICP-MS) for the plagioclase and clinopyroxene minerals in the low grade metamorphosed (under the greenschist facies) basalt samples? If yes, what kind of limitations do we have because of the metamorphism effects?
In other words, to determine the possible mantle source, which pertinent minerals can be used in the same samples (low-grade met. basalts) for the in-situ Pb-Hf-Nd methods?
I think LA-ICPMS is one of the robust methods to study metamorphism by in-situ isotope measurements on minerals involved in the metamorphism. It provides detailed information about the geologic process minerals experienced than analysing bulk minerals through wet chemistry on MC-ICPMS. With LA-ICPMS, you are on driving seat!
Concentrations of Pb are likely to be rather low, especially in cpx. This may make it more difficult to get very precise measurements, especially if you want to use ratios over 204Pb. Clinopyroxene is not stable at greenschist facies, so if you still have cpx in the sample, it must be a relic, and hopefully not much affected by metamorphism. For plagioclase, you would have to check whether it is still the original igneous plagioclase, or that it has been metamorphosed to albite. I do not know the age of your samples, but if they are more than a few Ma, then you will also have to correct for the presence of U and Th that will have decayed in the mean time.
Thanks a lot for the contribution, Assoc. Prof. Elburg. I will consider your suggestions.
Zeolite alteration I would have thought useful. In which case Sr, Rb, Hf, Pb, U could all be beneficial isotopes
Many thanks for all comments,
The metamorphism grades of my samples are mostly greenschist facies. Therefore, I have some limitations owing to the metamorphism effects. As far as I understand from the literature and your comments, especially, using of the Sr and Pb isotopes are risky because of the absence of pertinent minerals in the mafic-primitive rocks. As Prof. Elburg mentioned, they (pyroxene, plagioclase) can be altered easily under the greenschist metamorphism conditions. Maybe, the whole rock Nd-Hf isotope system (instead of the in-situ) can be used for the primitive basalt samples to minimize the effect of metamorphism?.
However, for the in-situ method, the Hf and Nd maybe Pb isotopes could be performed for the more resist minerals (zircons, monazites) in the more evolved rocks such as meta-rhyo-dacite, granites. The using of more resist minerals can be useful to avoid the effects of metamorphism.
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