Anthi, Jim and others,
At this juncture, I'd like to put in a plug for the very useful term
"pyribolite", coined by Asger Berthelsen forty years ago to denote a
metamafite consisting of pyroxene, amphibole and plagioclase, which it would
be misleading to call amphibolite. Berthelsen (Meddelelser om Gronland, Bd.
123, Nr. 1, 1960) defined pyribolite to be a metamafite with an amph:px
ratio ranging from 66:33 to 33:66 but I personally take the liberty of
broadening that range to take in the bulk of high-grade mafic rocks that
cannot in good conscience be termed amphibolites. For metamafites with >50%
plagioclase, Berthelsen coined the term "pyriclasite".
I am aware that J.B. Thompson in 1970 took over Johannsen's (1911)
collective noun for pyroxene and amphibole, "pyribole", and proposed it for
minerals with combined pyroxene and mica-like structural units but there's
hardly much room for confusion: anyway Berthelsen preceded Thompson by 10
years.
Cheers.
Tom Frisch
________________________
Thomas Frisch
Geological Survey of Canada
601 Booth Street
Ottawa, ON K1A 0E8
Canada
E-mail: [log in to unmask]
> Jim,
> There must be some misunderstanding. The rock I am talking about WAS an
> amphibolite which has undergone contact metamorphism due to a granodiorite
> intrusion. Contact metamorphism of this amphibolite resulted in the
> formation of the present cpx-opx-plag 'hornfelses, in which relics of the
> original amphibolite occur in form of patches.
> I hope this clarifies what I meant in my previous e-mail.
>
> cheers
> Anthi
> Dr Anthi Liati
> Institute of Isotope Geology and Mineral Resources
> Department of Earth Sciences
> ETH-Zentrum
> Sonneggstr. 5, 8092 Zürich
> Tel. ++41 1 632 6607
> ++41 1 632 3764 (secretary Mrs. Britt Meyer)
> Fax ++ 41 1 632 1827
>
>
>
>
> At 15:41 01.11.01 -0500, you wrote:
> >Anthi:
> >
> > FWIW, with cpx+opx your assemblage is granulite or
> pyroxene-hornfels facies, not 'amphibolite'. I agree totally that the
> rocks still may be 'amphibolite', and I share that use of the terminology
> for the rock. Just thought this distinction might deserve mention.
> Everyone stay safe.
> >
> >
> >JIM ECKERT
> ><[log in to unmask]>
> >------------------------------------------------------------
> >James O. Eckert, Jr., Ph.D
> >Department of Geology and Geophysics, Yale University
> >------------------------------------------------------------
> >
>
> -----------------------------------------------------------------------
>
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