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GEO-METAMORPHISM  August 2010

GEO-METAMORPHISM August 2010

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Subject:

Re: Major element closure temperatures in high-grade garnet

From:

Alexander Schmidt <[log in to unmask]>

Reply-To:

Metamorphic Studies Group <[log in to unmask]>

Date:

Fri, 6 Aug 2010 16:07:40 +0200

Content-Type:

text/plain

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  Yes I have considered this too. But if other phases break down 
sequentially, liberating their HREE while garnet grows, would´t this at 
least yield some sort of major element zoning? They do not necessarily 
always deliver a steady amount of major elements, right?




Am 06.08.2010 15:52, schrieb Stephen Daly:
> Have you considered the possibility that the zoning (or lack of it) is 
> controlled by material supply, i.e could the bell shaped REE and Y 
> curves reflect simultaneous growth of or sequestration by another 
> REE-bearing phase, while the majors remain available?
> Stephen
>
> ----- Original Message -----
> From: Alexander Schmidt <[log in to unmask]>
> Date: Friday, August 6, 2010 14:43
> Subject: Re: Major element closure temperatures in high-grade garnet
> To: [log in to unmask]
>
> > Ok, thanks for the answers so far.
> > What if we consider an eclogite garnet with peak temperatures
> > around 800°C (not necessarily very high grade I know), how can I
> > derive a rough estimate of the diffusion "speed", and therefore
> > also infer a rough closure temperature, for these elements? Will
> > it roughly be Mg<Fe<Mn<Ca<Lu?
> > The samples I have all show no zoning in the major elements at
> > all, but really good bell shaped profiles for Lu, Y, Yb, Dy, Ho,
> > Er & Tm. In my opinion, these garnets had enough time for the
> > major elements to diffuse/homogenize completely, while the HREE
> > have such a high "closure temperature" that nothing happened at
> > all, or diffusion speed is so slow that it would take much
> > longer to homogenize. But, without some evidence I can hardly
> > justify this assumption.
> >
> > Alexander
> >
> >
> >
> > Am 06.08.2010 14:09, schrieb Bruce Yardley:
> > >Eric, we miss you! Unfortunately Alexander, 35 years of
> > intensive research on this has got us to the point that we now
> > know it is not that simple. The work I published in 1977 is
> > still pretty applicable to the case of the onset of diffusion in
> > garnets in simple prograde metamorphism of sediments. However
> > there are rare examples of much higher grade garnets retaining
> > zoning, suggesting that in the absence of an aqueous fluid at
> > lithostatic pressure, things may be different. And since the
> > first thing that goes during cooling is the fluid pressure, it
> > may not be so easy to extrapolate results from prograde wet
> > sequences to retrograde dry ones. If you wanted to, you could
> > probably back the information out from natural examples
> > containing only one other Fe-Mg mineral, but if it was that easy
> > it would have been done.
> > >
> > >Bruce
> > >
> > >
> > >Professor Bruce Yardley
> > >School of Earth and Environment
> > >University of Leeds
> > >Leeds LS2 9JT
> > >UK
> > >Tel. +44 (0)113 343 5227
> > >
> > >Currently at: Sektion 3.3, Deutsches GFZ, Telegrafenberg, 14473
> > Potsdam, Germany
> > >________________________________________
> > >From: Metamorphic Studies Group [GEO-
> > [log in to unmask]] On Behalf Of Alexander Schmidt
> > [[log in to unmask]]
> > >Sent: 06 August 2010 12:18
> > >To: [log in to unmask]
> > >Subject: Major element closure temperatures in high-grade garnet
> > >
> > > Dear all,
> > >
> > >I am looking for a, let´s say list, with "closure temperature"
> > estimates>of Mg, Fe, Mn and Ca in high-grade garnets. I know
> > that the term closure
> > >temperature might be inappropriate in this case, yet there has
> > to be
> > >some estimate at which point during cooling these elements stop
> > to diffuse.
> > >
> > >regards,
> > >Alexander
> > >
> > >--
> > >Dr. Alexander Schmidt
> > >Institut für Erd- und Umweltwissenschaften
> > >Universität Potsdam
> > >Karl-Liebknecht-Strasse 24/25
> > >14476 Potsdam
> > >Tel: +49(0)331-9775786
> > >
> > >----------------------------------------------------------------
> > ---------------------------
> > >
> > >This email message is intended only for the use of the named
> > recipient. Information contained in this email message and its
> > attachments may be privileged, confidential and protected from
> > disclosure. If you are not the intended recipient, please do not
> > read, copy, use or disclose this communication to others. Also
> > please notify the sender by replying to this message and then
> > delete it from your system.
> > >
> >
> > --
> > Dr. Alexander Schmidt
> > Institut für Erd- und Umweltwissenschaften
> > Universität Potsdam
> > Karl-Liebknecht-Strasse 24/25
> > 14476 Potsdam
> > Tel: +49(0)331-9775786
> >
> > -----------------------------------------------------------------
> > --------------------------
> >
> > This email message is intended only for the use of the named
> > recipient. Information contained in this email message and its
> > attachments may be privileged, confidential and protected from
> > disclosure. If you are not the intended recipient, please do not
> > read, copy, use or disclose this communication to others. Also
> > please notify the sender by replying to this message and then
> > delete it from your system.
>
> Professor J. Stephen Daly
> Graduate Studies Co-ordinator
> Director, National Centre for Isotope Geochemistry
> UCD School of Geological Sciences
> Science Education and Research Centre (West)
> University College Dublin
> Belfield, Dublin 4, Ireland
> Phone: +35317162327, +353872051198 (mobile)
> Fax: +35312837733
>

-- 
Dr. Alexander Schmidt
Institut für Erd- und Umweltwissenschaften
Universität Potsdam
Karl-Liebknecht-Strasse 24/25
14476 Potsdam
Tel: +49(0)331-9775786

-------------------------------------------------------------------------------------------

This email message is intended only for the use of the named recipient. Information contained in this email message and its attachments may be privileged, confidential and protected from disclosure. If you are not the intended recipient, please do not read, copy, use or disclose this communication to others. Also please notify the sender by replying to this message and then delete it from your system.

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