 |
 |
Better yet, also give us some modal data. I think a sensible rock name would be both simple and non-genetic (as Pavel suggested) but also would depend on what the relative proportions of the minerals are. For example, a garnet-hornblende-epidote-phengite-rutile-quartz rock would have a very different name if it were 60% quartz than if it were 60% hornblende or 60% phengite. I also have some doubt as to the utility of even providing a name for an obviously polygenetic "assemblage" like this one. Bob T. Dr. Robert Tracy Professor of Geosciences Associate Department Head Director, Museum of Geosciences Virginia Tech Blacksburg VA 24061-0420 540-231-5980 540-231-3386 (F) On Dec 18, 2014, at 1:11 PM, Nuno Leal <[log in to unmask]> wrote: > Dear Santanu: > Can you shows us some photos of observations under the microscope ? > Best regards > Nuno Leal > > > -----Mensagem original----- > De: Metamorphic Studies Group [mailto:[log in to unmask]] Em nome de Santanu Kumar Bhowmik > Enviada: 17 de dezembro de 2014 15:13 > Para: [log in to unmask] > Assunto: Rock Nomenclature > > 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)