Dear Trisrota,
Ever heard about dissolution-precipitation as a mechanism for mineral
re-equilibration. See numerous papers by Putnis and coworkers on this
topic. Serpentinization is an essentially fluid-driven processes and
solid-state diffusion is thought to play a minor role during this
alteration.
Oliver
--
Oliver Plümper
Centre for Physics of Geological Processes (PGP)
University of Oslo
Sem Selands vei 24
NO-0316 Oslo
Norway
Phone (Office): +47 22 85 60 51
www.fys.uio.no/pgp/
http://www.uni-muenster.de/DELTA-MIN/students-postdocs/plumpero.html
On Sat, 17 Sep 2011 22:52:37 +0530, Trisrota Chaudhuri
<[log in to unmask]> wrote:
> Thanks to all for enlightening me. only I wonder with my very small
> knowledge, why does this diffusion goes up to grain boundaries (needs
> a long way for the elements to travel simply by diffusion ), why not
> symplectites. I'll definitely go through the paper by Prof Evans,
> hope
> I'll get more light on this.
> Regards and thanks again to all.
> Trisrota
>
> On Sat, Sep 17, 2011 at 7:48 PM, Kees Linthout wrote:
>
> Trisrota, John, Peter et al.:
>
> I wonder if Cr in spinel of altered peridotite stems from olivine,
> which is not a Cr-loving silicate.
>
> Kees L.
>
> Op 17/09/2011 15:41, Robert Tracy schreef:
>
> Trisrota, John, Peter et al.:
>
> I believe the old term (and maybe current as well) among
> opaque-mineral folks is "ferrit-chromit", since this phase that John
> and Peter refers to is typically a magnetite - Cr-spinel solid
> solution. I have commonly seen it as well in serpentinized
> ultramafic rocks, and sometimes it can even persist through the
> prograde metamorphic metamorphic process into amphibolite facies and
> possibly even beyond.
>
> Bob T.
>
> On Sep 17, 2011, at 5:10 AM, Clemens, JD, Prof wrote:
>
> Hi Trisrota,
>
> This is an almost universal feature of rocks in which mafic minerals
> have been serpentinised or altered to talc. The cause is simple, as
> you suspect. The new magnesian hydrous minerals are unable to
> accomodate all the Fe released by the reaction of the olivine or
> pyroxene into their crystal lattices, at the conditions of
> alteration.
> It thus expresses itself as magnetite-rich spinel oxide.
>
> Cheers,
> JC
>
> John D. Clemens
> Professor in Geology& Exec. Head
> Dept of Earth Sciences, University of Stellenbosch,
> Private Bag X1, 7602 Matieland, South Africa
> tel: +27 (0)21 808 3159 fax: +27 (0)21 808 3129
> e-mail:[log in to unmask] [3]
> web page:http://www.sun.ac.za/geo/people/clemens_e.htm [4]
> ________________________________________
> From: Metamorphic Studies Group [[log in to unmask]
> [5]]
> On Behalf Of Trisrota Chaudhuri [[log in to unmask] [6]]
> Sent: 17 September 2011 10:25
> To:[log in to unmask] [7]
> Subject: Texture in olivine cumulate
>
> Dear all,
> I'm getting a typical texture of olivine cumulate rocks in thin
> sections (photo attached), in which olivines are extremely altered
> into serpentine and/or talc. But the interesting thing is that every
> altered olivine grain has a thin rim of opaques along their grain
> boundaries. Is it possible that the olivine, due to alteration,
> released some extra Fe/Mg, which might not been needed to form the
> altered product, and hence concentrated along olivine grain
> boundaries? Or something else like grain boundary exsolution has
> taken
> place? Please enlighten me.
> Regards,
>
> --
> Trisrota Chaudhuri,
> JRF of Indian Statistical Institute and Jadavpur University,
> Kolkata, India.
> Robert Tracy
> Professor of Geosciences
> Virginia Tech
> Blacksburg VA 24061-0420
> O: 540-231-5980
> F: 540-231-3386
>
> --
> Trisrota Chaudhuri,
> JRF of Indian Statistical Institute and Jadavpur University,
> Kolkata, India.
>
>
>
> Links:
> ------
> [1] mailto:[log in to unmask]
> [2] mailto:[log in to unmask]
> [3] mailto:[log in to unmask]
> [4] http://www.sun.ac.za/geo/people/clemens_e.htm
> [5] mailto:[log in to unmask]
> [6] mailto:[log in to unmask]
> [7] mailto:[log in to unmask]
--
Oliver Plümper
Centre for Physics of Geological Processes (PGP)
University of Oslo
Sem Selands vei 24
NO-0316 Oslo
Norway
Phone (Office): +47 22 85 60 51
www.fys.uio.no/pgp/
http://www.uni-muenster.de/DELTA-MIN/students-postdocs/plumpero.html
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