Hassina,
The assemblage hercynite-quartz requires only HT but not UHT
conditions unless forming at P > 10 kbar. Finding a spinel with
hercynite-gahnite±spinel solid solution is commonplace in granulite
facies metapelites. I've seen that association in Grenville-age
granulites from NW Adirondacks, and near Parry Sound, Ontario, W.
Brazil, and S. Norway, and in Archean rocks from the Wind River Range
of Wyoming, at Manitouwadge, Ontario, and C. Australia.
eric
On Dec 10, 2004, at 9:39 AM, Dr H.MOURI wrote:
> Eric and others,
> apologies if my message is out of the topic of the discussion, I did
> not
> fellow from the start, just from Eric's email - for interest I would
> like to
> add one info about cor-magn-hercynite: I reported the same as what Eric
> mentioned below (corundum in magnetite-hercynite, with sillimanite and
> quartz) bearing rocks in Namaqualand (South Africa) (see Mouri et al,
> Mineralogical Magazine Vol., 67(5), 1015-1021) where spinel and quartz
> are
> observed in contact indicating UHT conditions, I did some calculation
> of T
> where corundum coexist with magnetite-spinel (see Mouri et al., 2004,
> JOURNAL OF MINERALOGICAL AND PETROLOGICAL SCIENCES SPECIAL ISSUE ON
> Ultrahigh temperature metamorphism and deep crustal processes). It
> seems
> that when corundum is present with hercynite - magnetite - it might
> indicate
> UHT conditions - where melting and migmatite forming processes are
> possible
> depending on the source composition of course (?).
> Cheers
> hassina
>
>
> ----------------------------------
> Dr Hassina MOURI
> Acting Head of Department
> Department of Geology
> University of Pretoria
> Pretoria 0002
> Republic of South Africa
>
> Tel (office): (+27 12) 420 24 56
> Fax: (+27 12) 362 52 19
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> http://www.up.ac.za/academic/geol/pers/Hassina.html
>
> "The important thing is not to stop questioning." - Albert Einstein
>
>
>
>
>
>> All,
>> We also reported corundum in complex textures with hercynite,
>> magnetite and hogbomite in sillimanite gneisses. The assemblage may
>> form during early retrogression by oxidation of a complex high-T
>> spinel
>> solid solution.
>> eric
>>
>
>
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