Olivier,
We have exchanged comments some 5 years ago, and you did not
satisfy my concerns then. As I noted in my 1989 review on
thermobarometry, Buseck & Huang (1985) found with TEM that the
graphitization process involves nucleation and growth of
submicroscopic graphite in the amorphous (hydro)carbons. That means
that any bulk measurement is averaging the amounts of the new nuclei
and the older carbonaceous material, as I said. This is not the kind
of system one wants to apply for thermometry. Deformation, high F/R
ratios and indeed fluid chemistry may aid in the amount of
transformation, as I noted in 1989. You make some similar comments
in your e-mail comments -- so how can this operate as a thermometer
if it also a strain-meter, a methane barometer, a rate meter?
If anyone wants a pdf file of my 1989 review I can send them a
copy.
Almost doesn't mean isochemical. Polymorphic changes are often
very sensitive to minor solid solution (and in this case, the nature
of the less than perfect crystallinity still needs a deeper
understanding). Methane pressures could not have an effect on
equilibrium, isochemical graphitization. I maintain it is a non-
equilibrium process.
We see crystals of graphite in greenschist facies marbles from
the Grenville that are euhedral. Are you saying these are
aggregates? We also see in these marbles that graphite is not
necessarily oriented relative to schistosity, so the foliation game
is problematical there (it is probably OK for phyllites).
eric
On Mar 6, 2008, at 4:15 AM, [log in to unmask] wrote:
> Few (late) comments from the field, anybody interested may contact me
> directly for further details.
>
> Thanks Steve for the quotation, although some other groups use this
> approach now. More generally, using graphitization as a
> geothermometer is
> a rather old idea, Buseck and Huang (1985), Wopenka and Pasteris
> (1993, Am
> Min) and references therein must be cited. In our JMG 2002 paper,
> we have
> proposed a first quantitative geothermometer based on Raman
> spectroscopy
> of Carbonaceous Material.
> PDF at: http://www.geologie.ens.fr/~beyssac/Beyssac-jmg-02.pdf
>
> Eric:
> - graphitization (T>330C) is an almost isochemical solid state
> transformation as hydrocarbons are released at lower T,
> - regarding the T-t tradeoff which is a key question, please check
> discussion section)
> for an experimental approach,
> http://www.geologie.ens.fr/~beyssac/Beyssac-ejm-03.pdf
> for a geologic point of view,
> http://www.geologie.ens.fr/~beyssac/Beyssac-tectonics-07.pdf
> and also the kinetic models for vitrinite reflectance by Sweeney and
> Burnham (AAPG Bul 1990),
> - regarding orientation effects with Raman spectroscopy, Tan et al
> (Phil
> Mag Royal Soc A, 2004) nicely showed that it is virtually
> negligible using
> an argon laser on highly cristallized graphite, so does it with
> generally
> disordered (polycrystalline) carbon in metamorphic rocks. Note that
> you
> can also reduce this effect cutting thin sections perpendicular to the
> foliation and using a depolarized laser (various possibilities for the
> setup).
>
> Olivier
>
> ---------------------------------
> Olivier Beyssac
> Laboratoire de Geologie
> CNRS-ENS
> 24 rue Lhomond
> F-75005 Paris
> http://www.geologie.ens.fr/~beyssac
>
>
>
>
>
>
> All,
> Mark Brandon and his group looked at the Beyssac approach and
> modified
> it to apply to low grade marbles in Crete. The problems I have with
> this system is that it is an irreversible open-system reaction that
> must have a t-T dependence. It is irreversible because crystalline
> graphite is always more stable than hydrocarbons, and it is
> open-system because the hydrocarbons have additional components such
> as H and perhaps O, N, making formation of graphite non-isochemical.
> That makes it interesting but complicated and not the best thermometer
> to first apply. There is also a question of orientation effects
> perturbing the results.
> cheers,
> eric
>
>
> On Feb 27, 2008, at 6:49 AM, Steven R. Dunn wrote:
>
>> John,
>>
>> I'm glad to learn you're working on a second edition. The first
>> edition
> is simply wonderful! I look forward to the second.
>>
>> Regarding calcite-graphite carbon isotope thermometry, I am glad you
> included it in the first place. But there are two "calibrations" in
> use, Dunn and Valley (1992) and Kitchen and Valley (1995). Dunn
> (2005)
> shows that the Dunn and Valley (1992) calibration gives excellent
> results from 500 to 650C. Several other studies conclude that Kitchen
> and Valley (1995) is excellent in the range 650 to 800C, and that is
> where the current understanding remains. I'm not sure why you cited
> Morrison & Barth (1993) in this table. They applied this thermometer
> and concluded that Dunn and Valley (1992) gave the best results, but
> they did not actually add anything to the thermometer.
>>
>> I've attached Dunn (2005), as if you have time to look into every
>> paper
> on every geothermometer in use today. :)
>>
>> Also, Olivier Beyssac and coworkers have been using a geothermometer
> based on the laser Raman spectra of graphite (a single mineral
> geothermometer). To date, they are the only ones using it, but they
> have applied it with apparently reasonable results in numerous
> terranes.
> I attached their "calibration" paper in case you're interested, and
> would be happy to provide additional information if you want it. I
> published an abstract with Jill Pasteris showing that graphite in
> Grenville marble has matured at lower T than the graphitic pelites
> used
> by Beyssac. The full manuscript will be submitted soon.
>>
>> Best Regards,
>>
>> Steve
>>
>>
>> John Winter wrote:
>>>
>>> Dear colleagues,
>>>
>>>
>>>
>>> I am updating a table of geothermometers and geobarometers- Table
>>> 27-4
> from my text, based on Frank Spear’s (1993) Table 15-1. This is a
> fairly large task, particularly here in remote Hawaii without a major
> library (OK, not likely to get sympathy I suppose). I’m turning to you
> for help, hoping that several of you have maintained updated
> references
> for your research and advanced coursework to augment my search. If you
> have such a list, even if addressing only a limited number of
> equilibria, please send it on to me at the email below (don’t merely
> Reply to this, as I too often do, and send your input to the whole
> group!). I’d be happy to send the updated table as a pdf file to all
> interested (or wait for the second edition to appear). Thanks so much.
> John
>>>
>>>
>>>
>>> John D. Winter
>>> Department of Geology
>>> Whitman College
>>> Now at: PO Box 551735
>>>
>>> Kapa'au, HI 96755
>>>
>>> (808) 889-6901
>>> [log in to unmask]
>>> http://www.whitman.edu/geology/winter/
>
>
>
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