Dear Pulak, 7/20/00
If your rocks crystallized above about 8 kb, the Ms-Pg
geothermometer may be seriously flawed. However, if they crystallized at
8Kb or below, it may be at least worth a try -- especially if your rocks
contain graphite so that the Fe3+ content of the muscovite won't be
unusually high. Have a look at the empirical calibration by Blencoe et. al.
(1994, and references therein) in Geochemica Cosmochimica Acta. Also, there
is a more recent thermo/experimental treatment by Roux and Hovis in J. Pet.
I am aware of still newer work on Ms-Pg pairs, but the author has not yet
sent me the preprint (though he has promised to do so!), so I'll leave it
to him to provide you with his still more recent imput and insights.
Cheers, Chuck
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>Dear All,
> Thank you very much for your erudite suggestion. This has clarified many
>confusion. I am trying to test the accuracy of the existing Gt-Bt
>thermometers in the low grade rocks. I thought Al2SiO5 triple point could be
>a standard. I noted a large difference in temperature between Mt Moosilauke
>and Picuris range irrespective of the thermometers (the latter being always
>higher). So I was in a fix whom should I blame- the thermometers or the
>triple point ! Now it is clear that the so called triple point is only
>present in the experimental runs. In my rocks I also have coexisting
>muscovite –paragonite. Can I use this pair as a reliable geothermometer? I
>shall be thankful to you for your comments.
>
>Nandini
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