Dear Jarek,
You are indeed correct. There are minor relics of Gln within Hbl, suggesting that the prograde path passed through the epidote blueschist. But at the metamorphic peak, Gln is completely absent, and the main amphibole is Hbl. So, the problem of nomenclature remains.
Thanks.
Santanu
----- Original Message -----
From: "Jarek Majka" <[log in to unmask]>
To: "Metamorphic Studies Group" <[log in to unmask]>, [log in to unmask]
Sent: Wednesday, December 17, 2014 9:22:32 PM
Subject: Re: [geo-metamorphism] Rock Nomenclature
Santanu,
It seems to me like a former blueschist, which has undergone some
heating. Have you searched carefully for a proper Na-amphibole relicts
in your hornblende?
Best,
Jarek
> Dear Colleagues,
>
> I am seeking your suggestions on the nomenclature of a metamorphic rock with the assemblage garnet+hornblende+epidote+phengite+rutile+quartz. This assemblage which became stable during peak metamorphism yielded P-T estimate of ~ 15-16 kbar,~ 590-610 °C. If this assemblage is evaluated with metamorphic rocks that are related to metamorphism during subduction initiation, the closest rock name that comes to my mind is garnetiferous amphibolite. However, in the strictest sense, the rock, in the absence of plagioclase cannot be an amphibolite, if we use amphibolite in facies sense. At the same time, the estimated P-T range lies in the eclogite facies, also supported in part by complete elimination of plagioclase. However, with omphacitic clinopyroxene being absent, the rock is also not an eclogite in the strictest sense. One additional information in this regard is that Na in the protolith is completely partitioned in Hbl, which shows substantial presence of Na in the M4 site, apart from its general occurrence in the A site.
>
> Your comments and observations are welcome.
>
> With regards,
>
> Santanu
> -------------------------------------------------------
> Dr. Santanu Kumar Bhowmik
> Professor
> Department of Geology & Geophysics
> Indian Institute of Technology
> Kharagpur-721 302
> India
> Mobile:+919434041791
> Telephone:+91-3222-283390(O), 283391, 279766(R)
--
Jaroslaw Majka Ph.D., Docent
Researcher and EMP Lab Manager
Department of Earth Sciences
Uppsala University
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SE-752 36 Uppsala, Sweden
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