David Snoeyenbos did work on UHT-HP felsic granulites from the Snowbird
Tectonic Zone in the western Canadian Shield. The rocks appear to be
garnet-rich restites from a lower crustal HP melting event. He has images
of garnet grains with beautifully oriented (and exsolved?) needles of
rutile.
Snoeyenbos, D. R., Williams, M. L., and Hanmer, S., 1995, Archean
high-pressure metamorphism in the western Canadian Shield: European
Journal of Mineralogy, v. 7, p. 1251-1272.
>>>> proyer <[log in to unmask]> 2008/09/26 10:45 AM >>>
> Hello everybody,
>
> hope some of you can help me out on two questions related to each other:
> 1) Is there a source which clearly defines when to call a mineral phase
> unmixing from a solid solution "exsolution" or "precipitate"?
> 2) Do you know of any article expaining explicitly (reaction equations
> etc.) how rutile unmixes from high-tempertaure garnet?
> I know of three such papers for ultrahigh-pressure garnets (Van
> Roermund, 2000; Zhang et all. 2003 and Yang & Liu, 2004),
> but none for granulite facies rocks etc.
> Please let me know if you have come across or even authored any such
> references.
>
> Sincerely,
> Alexander Proyer
> University of Graz, Austria
>
> Please find our Email Disclaimer here: http://www.ukzn.ac.za/disclaimer/
>
--------------------------------------------------
Gregory Dumond
NSF Earth Sciences Postdoctoral Fellow
Department of Earth, Atmospheric, and Planetary Sciences
MIT, 54-1024
Cambridge, MA 02139
http://www.geo.umass.edu/grads/dumond/
"There is not enough darkness in all the world to put out the light of
even one small candle."
--Robert Alden
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