Dear Johann and all,
I'm one of those who rather routinely use the SEM/EDS to estimate the
bulk composition for phase diagram calculations. I started doing this
5-10 years ago (I don't remember exactly and would have to look if this
info was of importance) for many, not only for domainal samples.
The reason is very simple - it's fast, cheap and relatively reliable (I
have checked reproducibility and compared with "standard" bulk rock
analyses on various samples) + offers obviously the possibility to
select the analysed area in heterogeneous samples or those having zoned
minerals.
It's worth stressing out that I don't speak about estimating the
proportion of the phases from a BSE image and then multiplying them by
their composition (obtained through EDS or EPMA WDS) - which I also did
in the past. I'm speaking about analysing areas of thin sections
directly using the SEM/EDS. My point of view is that the result may not
be extremely precise/accurate (although, as noted above, I find it
entirely satisfactory), but the uncertainty related to the estimation of
the equilibrium volume is significantly larger. So a reflexion about the
sensitivity of a calculated diagram to moderate variations of the bulk
composition is necessary in any case.
I'm still doing bulk rock chemical analyses (ICP-AES/MS + titration) if
I need info about trace elements and/or the Fe2/3 ratio. We never used
XRF because if was not available here and it was not in "my tradition" ;-).
Cheers,
Pavel
Le 01/06/2018 à 11:22, johann diener a écrit :
> Good Day All,
>
> I am curious when and why the kind of BSE and EMPA-based techniques
> discussed here became routine for determining bulk compositions to use
> in pseudosection calculations. It started with folks who wanted to model
> reaction textures in strongly domainal rocks that have small
> equilibration volumes, but seems to now almost be the preferred method
> for any situation. What�s wrong with a good old careful XRF analysis?
> Is it that XRF labs are not glamorous enough to be funded any more and
> are becoming few and far between?
>
> Cheers,
> Johann
>
> Johann Diener
> Department of Geological Sciences
> University of Cape Town
> Private Bag X3
> Rondebosch 7701
> South Africa
> ph +27 (0)21 650 2926
> fax +27 (0)21 650 3783
--
Pavel PITRA
Géosciences Rennes [log in to unmask]
Université Rennes 1 tel: (++33) 2.23.23.65.06
Campus de Beaulieu - Bat. 15
F - 35 042 RENNES CEDEX
FRANCE http://www.geosciences.univ-rennes1.fr/
https://geosciences.univ-rennes1.fr/interlocuteurs/pavel-pitra
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