I have observed ep + q symplectites in retrograde eclogites from the Tromsoe nappe of the uppermost allochthon of the Scandianvian Caledonides. In these rocks they appear to occur between secondary plagioclase and relict HP/UHP garnet, but in most cases no garnet is observed. I have attached a microphoto to show how it may look like.
Fra: Metamorphic Studies Group [mailto:[log in to unmask]] På vegne av Francois Guillot
Sendt: 16. oktober 2003 09:37
Til: [log in to unmask]
Emne: Re: epidote symplectite
I would rather expect albite-epidote associations from plagioclase
What is the size of the individual crystals, the pattern and shape of
the quartz-epidote assemblages (a photo would be useful) and was any
EMPA tried on the quartz?
Is there any chance to replace albite by quartz during a further episode?
> It is difficult to make epidote-quartz by decompression of
>plagioclase-bearing rocks. Epidote could form by isobaric cooling
>but also requires oxidation unless it is forming from hematite.
>>Hello to all in this group from someone who joined recently, and who is more
>>of a structuralist, with a growing interest in metamorphic petrology. I
>>think you may be able to help me on a question that arises from some of my
>>recent work in a granite-gneiss complex that crops out in the Late Archean
>>Abitibi granite-greenstone belt, Ontario. I will briefly synthesize.
>>The amphibolite-grade tonalite gneiss and a large tonalite-granodiorite
>>batholith that make up a large, refolded structural dome have a common
>>foliation within them that likely formed as a result of flattening during
>>the doming. In the gneiss, it is clearly a solid state tectonite fabric, and
>>in the batholith it is a magmatic state fabric. That foliation was folded by
>>regional-scale folds as the batholith was crystallizing and fractionating.
>>Within that doming-related (earlier) foliation, in the gneiss and in the
>>plutons, there is a very common occurrence of mm-scale epidote-quartz
>>symplectites. They occur in grain contact with plag and qtz and also (but
>>less often) with Kf, hbl, mt and titanite. Following the advice of an
>>esteemed member of the metamorphic community, I am interpreting the
>>symplectites to represent a solid state retrograde feature.
>>I also interpret they indicate a fairly rapid decompression, related to
>>exhumation in the hinge zones of the regional scale refolds of the dome.
>>My question is, do you know of other similar examples? I have looked through
>>the literature fairly thoroughly (I think) and I have not found
>>documentation of the same textures in similar rocks. This is clearly not a
>>standard hydrothermal greenschist grade overprint such as is found in many
>>Any hints where I might find such textures and such an assemblage
>>Thanks to all who may respond. keith
>>Keith Benn, Associate professor
>>Department of Earth Sciences, University of Ottawa
>>140 Pasteur Street, Ottawa, ON K1N6N5, Canada
>>office tel: +1-613-562-5800 x6858
>>lab tel: +1-613-562-5800 x6833
>>dept fax: +1-613-562-5192