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
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> > read, copy, use or disclose this communication to others. Also
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> > >
> >
> > --
> > 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
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>
> 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
-------------------------------------------------------------------------------------------
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