Dear Antonio,
Agree with your suggestion on tectonic setting, other than that TMax of the rock concerned was not high enough to initiate partial melting of the "amphibolite" rock.
In the context of metamorphic facies, the problem still remains as I indicated in my initial mail: whether it's an Hbl eclogite (Pl-free, but without omphacite) or an amphibolite (dominantly Hbl-rich, but without Pl)? Any reference that discussed this specific issue?
Antonio, thanks for the list of relevant papers. Had a look at the majority of them.
With regards,
Santanu
----- Original Message -----
From: "Antonio Garcia Casco" <[log in to unmask]>
To: [log in to unmask]
Sent: Wednesday, December 17, 2014 10:02:02 PM
Subject: Re: [geo-metamorphism] Rock Nomenclature
Dear Santanu and all,
Neither amphibolitized eclogite (that normally has post-eclogite
albite/plagioclase) nor amphibolitized blueschist (that would retain
albite or produce plagioclase under amphibiolite facies conditions)
occur in the oceanic mélanges indicated below. There, tectonic blocks of
"amphibolite" (lacking plagioclase) occur in a serpentinite matrix
interpreted as formed in a subduction channel. Calculated pressures are
similar (15 kbar), though temperature is higher (700-750 ºC). In these
rocks both relatively high pressure and hydrous partial melting of MORB
"amphibolites" formed rocks lacking plagioclase which bear a similar
mineral assemblage as that indicated in the query. The tectonic scenario
is onset of subduction of a young hot oceanic lithosphere. A paragraph
in the first paper listed below is devoted to the raised problem of
nomenclature of these peculiar metabasite.
2008. GARCÍA-CASCO, A., LÁZARO, C., ROJAS-AGRAMONTE, Y., KRÖNER, A.,
TORRES ROLDÁN, R. L., NUÑEZ, K., MILLÁN, G., NEUBAURER, F., QUINTERO, I.
Partial melting and counterclockwise P-T path of subducted oceanic crust
(Sierra del Convento, E Cuba). Journal of Petrology 49, 129-161.
doi:10.1093/petrology/egm074
2009. LÁZARO, C., GARCÍA-CASCO, A., NEUBAURER, F., ROJAS-AGRAMONTE, Y.,
KRÖNER, A., ITURRALDE-VINENT, M.A. Fifty-five-million-year history of
oceanic subduction and exhumation in the northern edge of the Caribbean
plate (Sierra del Convento mélange, Cuba). Journal of Metamorphic
Geology, 27, 19-40. DOI 10.1111/j.1525-1314.2008.00800.x
2010. BLANCO-QUINTERO, I.F., GARCÍA-CASCO, A., ROJAS-AGRAMONTE, Y.,
RODRÍGUEZ-VEGA, A., LÁZARO, C., ITURRALDE-VINENT, M. A. Metamorphic
evolution of subducted hot oceanic crust (La Corea mélange, Cuba).
American Journal of Science, 310, 889–915. DOI: 10.2475/11.2010.01
If you are curious and want to know more about this rare case of
partial melting of a hot slab:
2007. GARCÍA-CASCO, A. Magmatic paragonite in trondhjemites from the
Sierra del Convento mélange, Cuba. American Mineralogist 92, 1232-1237.
DOI 10.2138/am.2007.2598
2008. LÁZARO, C., GARCÍA-CASCO, A. Geochemical and Sr-Nd isotope
signatures of pristine slab melts and their residues (Sierra del
Convento mélange, eastern Cuba). Chemical Geology. Chemical Geology,
255, 120-133.DOI 10.1016/j.chemgeo.2008.06.017
2011. BLANCO-QUINTERO, I. F., GERYA, T. V., GARCÍA-CASCO, A., CASTRO,
A. Subduction of young oceanic plates: a numerical study with
application to aborted thermal-chemical plumes. Geochem. Geophys.
Geosyst, 12, Q10012. DOI 10.1029/2011GC003717.
2011. Blanco-Quintero, I.F., Rojas-Agramonte, Y., García-Casco, A.,
Kröner, A., Mertz, D.F., Lázaro, C., Blanco-Moreno, J., Renne, P.R.
Timing of subduction and exhumation in a subduction channel: Evidence
from slab melts from La Corea mélange (eastern Cuba). Lithos, 127,
86–100. DOI 10.1016/j.lithos.2011.08.009
2011. BLANCO-QUINTERO, I. PROENZA J.A., GARCÍA-CASCO A., TAULER, E.,
GALÍ, S. Serpentinites and serpentinites within a fossil subdution
channel: La Corea melange, eastern Cuba. Geologica Acta, 9, 3-4,
389-405, DOI 10.1344/105.000001662,
2011. Lázaro, C., Blanco-Quintero, I.F., Marchesi, C., Bosch, D.,
Rojas-Agramonte, Y., García-Casco A. The imprint of subducion fluids on
subducted MORB-derived melts (Sierra del Convento mélange, Cuba).
Lithos, 126, 341–354. DOI 10.1016/j.lithos.2011.07.011
2011. BLANCO-QUINTERO, I.F.; LÁZARO, C.; GARCÍA-CASCO, A.; PROENZA, J.;
ROJAS-AGRAMONTE, Y. Barium-rich fluids and melts in the subduction
environment (La Corea and Sierra del Convento mélanges, eastern Cuba).
Contributions to Mineralogy and Petrology, 162, 395–413. DOI
10.1007/s00410-010-0603-2
2011. BLANCO-QUINTERO, I.F., GARCÍA-CASCO, A., GERYA, T. Tectonic
blocks in serpentinite melange (eastern Cuba) reveal large-scale
convective flow of the subduction channel. Geology, 39, 79-82. DOI
10.1130/G31494.1
Wish you happy Christmas
Antonio
--
Antonio Garcia-Casco
Professor of Petrology and Geochemistry
(http://www.ugr.es/~agcasco/personal/)
Department of Mineralogy and Petrology, University of Granada, Spain
(http://www.ugr.es/~minpet/)
Andalusian Institute of Earth Sciences, IACT, UGR-CSIC, Spain
(http://www.iact.ugr-csic.es/web_eng/index.html)
Tel: + 34 958 246613
El 2014-12-17 16:52, Jarek Majka escribió:
> 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)
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