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GEO-METAMORPHISM  2004

GEO-METAMORPHISM 2004

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Subject:

Re: sapphirine and corundum in mafic rocks

From:

Frank Beunk <[log in to unmask]>

Reply-To:

Metamorphic Studies Group <[log in to unmask]>

Date:

Tue, 24 Feb 2004 14:49:27 +0100

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (121 lines)

At 13:45 24-2-04 +0600, you wrote:

Another occurrence of sapphirine + corundum has recently been reported from 
the Guyana shield: Cordierite-sapphirine bearing pelitic gneiss with thin 
mafic layers which contain corundum in contact with magnetite. The corundum 
probably formed by exsolution from an Fe-rich spinel s.s. during cooling 
and contains 0.7 wt% Fe2O3, according to:
E.W.F. de Roever, J.M. Lafon, C. Delor, A. Cocherie, P. Rossi, C. Guerrot & 
A. Potrel, 2003. The Bakhuis ultrahigh-temperature granulite belt 
(Suriname): I. Petrological and geochronological evidence for a 
counterclockwise P-T path at 2.07-2.05 Ga. Géologie de la France, 2-3-4, 
175-205.
Frank


>Dear colleagues,
>
>I was asked by my colleague Eugene Sklyarov to send this e-mail for
>Metamorphic Studies Group. He can not comminicate with you via regular
>e-mail, obviously something must be wrong with this connection. Below
>is his letter including abstract:
>
>"I need consultation about unusual (at least for me) mineral assosiation:
>Amph+sapphirine+Cpx+Sp+Zo+/-corundum+/-Cr-Sp+/-kornerupine+/-Mus. Rocks
>are of mafic composition: 80-85%Amph (15-16%Al2O3), 10-15%Sapp. Some general
>information you can take from abstract below for IGC in Florence, where I
>suppose to present it in Arctica session. Can you advise me any reference
>about sapphirine and corundum in mafic rocks?
>Best regards
>Prof. Eugene Sklyarov
>Institute of the Earth's crust SB RAS,
>Irkutsk, Russia
>[log in to unmask]
>
>A.Kuzmichev, E.Sklyarov
>Blueschists and associated exotic rocks related to the South-Anjuy
>suture on the Big Lyakhov Is. (New Siberian Islands)
>
>The South-Anjuy suture is the trace of an Early Mesozoic ocean that closed at
>the beginning of Cretaceous. The suture separates two distinct structures. In
>the south there occur Permian-Jurassic island-arc terrains including the 
>Anjuy-
>Sviatoi Nos arc fragments. To the north continental block including North 
>Chukotka,
>the New Siberian platform and the East Siberian shelf is situated. The 
>block is
>believed to have been separated from the Arctic Canada in the course of the
>Amerasian oceanic basin opening. Blueschists and associated exotic rocks 
>of oceanic
>and island-arc origin are thrusted upon the edge of the platform and form 
>tectonic
>wedges or nappes among late Jurassic to Early Neocomian forland basin 
>deposits. The
>suture complexes include three distinct units (from NW to SE). 1) 
>Pillow-basalts
>geochemically similar to N-MORB. The K-Ar age of hyaloclastite corresponds 
>to Middle
>to Late Jurassic. The associated serpentinite contains harzburgite, 
>wehrlite and
>pyroxenite relics. 2) The blueschist-greenschist nappe including oceanic 
>gabbro, basalt
>with minor shale. The rocks reveal a complex metamorphic history; the 
>PT-conditons of
>HP stage are estimated as P more 8 kbar, T=400-500°C. 3) The amphibolite 
>complex after
>mafic-ultramafic suprasubduction layered intrusion showing the dunite to 
>leucocratic
>gabbro irregular succession. The ultramafics are mostly non-serpentinised 
>dunite to
>wehrlite and pyroxenite. Metamorphosed mafic cumulates contain mineral 
>assemblage with
>sapphirine and corundum. The plagioclase - hornblende pegmatites (180-210 
>Ma) were
>emplaced at the final stage at T = 650-700°C and P = 9-10 kbar. Our 
>palaegeographic
>interpretation of the above units is as follows. The first unit is a 
>fragment of the
>Jurassic South-Anjuy Ocean lithosphere. The second unit corresponds to a 
>subduction
>zone dipping under the Anjuy-Sviatoi Nos island arc. The mafic-ultramafic 
>layered
>complex represents a subarc magma chamber formed at the depth of 30-35 km 
>at the root
>of the same island arc. Each of above complexes shows analogue in the 
>South-Anjui
>region. So we assume that the true extension of the South-Anjuy suture 
>occurs on the
>Big Lyakhov Is. This conclusion does not fit the proposed earlier plain 
>rotational
>model of the Amerasian oceanic basin opening."
>
>Thank you in advance.
>Sincerely Yours,
>
>Igor
>
>Dr. Igor I.Likhanov
>Principle Researcher/Associate Professor
>Institute of Mineralogy & Petrography/Novosibirsk State University
>Siberian Branch Russian Academy of Sciences
>Prosp. Acad. Koptyuga 3
>Novosibirsk, 630090, Russia
>Tel. office: 07 3832-333672
>Tel. home: 07 3832-111574
>Tel. mobile: 8913-9353916
>Fax: 07 3832-332792
>Personal web page: http://www.uiggm.nsc.ru/~likhanov/
>e-mail: [log in to unmask]



-------------------------------------
Frank F.  Beunk
Faculty of Earth and Life Sciences, Vrije Universiteit
Dept. of Petrology
De Boelelaan 1085, room F348
NL-1081 HV  Amsterdam, Netherlands
T  +31-20-4447371
F  +31-20-6462457
E  [log in to unmask]

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