Thanks Dugald Camichael for your comments.
        I wish to mention your chlorite-prehnite faices that it does not
contain "gabbro" mentioned by Eskola(1915). The
prhenite+pumpellyite+chlorite  also cannot include metabasite. Knowing
the ACF approximation is too schematical, for metasidtes chorite is
ubioqutous and may not be referred to. I think the assemblages by  which
facies  is defined , needs compositional area covered in ACF. To be so,
we need actinolite or glaucophane or augite and ? talc. Many of ualtered
igneous  augite is so to speak stable relic of Eskola. Free energy of
igneous augite and Di-Hd required for ACF is differnet but the delta G
to decompoe AUGITE is not distinct from that of Di+ Hd then the driving
force to the reaction may not be large.


                                                Yours sincerely
                                                        Shohei Banno



1-23-16-104
Takano-higashihiraki
Sakyo-ku, Kyoto
606-8107, Japan
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-----Original Message-----
From: Metamorphic Studies Group [mailto:[log in to unmask]]
On Behalf Of Dugald Carmichael
Sent: Friday, October 17, 2003 7:22 AM
To: [log in to unmask]
Subject: Re: metam facies confusion


At 11:49 AM 16/10/2003 +0900, Shohei (Banno) wrote:
>To whom interested:
>         I never thought the Turner's system of defining hornfels
>series is useful,  But  I will  use the pyroxene hornfels facies in
>honour of Goldscmidt and Eskola.  We need Eskola(1939) 's faceis and
>modified Coombs facies, which are  zeolite, prehnite-actinolite and
>pumpellyite-actinolite facies. I think prhenite-pumpelllyite facies is
>confusing and better not to use.
>  ...

I agree except "prehnite-actinolite facies" should be renamed
prehnite-chlorite facies. The subassemblage prehnite+actinolite is too
Ca-rich to define a facies in metabasite bulk composition. This can be
appreciated on a conventional ACF diagram, where the prehnite-actinolite
tie-line does not cross the ACF tie-line diagnostic of any other facies.
With few exceptions, the same is true of the subassembage
prehnite+pumpellyite. But the prehnite-chlorite ACF tie-line cuts the
tie-line from actinolite (or so-called "relict igneous clinopyroxene")
to epidote, pumpellyite, lawsonite, plagioclase, or any metamorphic
zeolite. Hence the subassemblage prehnite+chlorite has a reaction
relationship to metabasite assemblages diagnostic of any other
Eskola/Coombs facies.  Clearly therefore, "prehnite-chlorite facies"
should have facies status in any set of facies based on mineral
assemblages in metabasites, but "prehnite-actinolite facies" and
"prehnite-pumpellyite facies" should not.

Cheers, Dugald