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 [[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
>
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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
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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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