Hi all,
I concur with the secondary flourescence effect problem. David Steele
and I presented a paper in the Perth microbeam conference in 2007 on
our electron microprobe analysis of zircons for Ti at high beam
currents. One effect seen is secondary flourescence up to 50 microns
into the 500 micron zircon crystals, arising from nearlby ilmenite
(disseminated). We tested the e-probe Ti analyses against SIMS (and I
have since done so against femto-ICPMS too), and found the rimward Ti
increases seen in the e-probe data (which we modelled too as function
of grain diameter) were an artifact. The actual Ti contents of these
zircons were high: 42 ppm on average in the particular sample, and
nearer 50 ppm in another, and so the minimum T of zircon growth was
about 915C (no problem there - the samples are from the Napier Complex).
Some of this is also described in my abstract from the MAPT meeting
this year - see the min soc website. Hope to publish it soon...
Regards,
Simon Harley
Quoting Andreas Möller <[log in to unmask]>:
> Dear all,
>
> I concur with John and quoted reference that secondary fluorescence is
> very important for trace element analyses and thermometry, as those
> people applying the Ca-in-olivine thermometer in peridotites very well
> know.
> This was brought home to us for Pb analysis when we did U-Th-Pb dating
> in thin section with synchrotron radiation.
> Schmitz et al.: Chemical U-Th-Pb dating of monazite by 3D-Micro X-ray
> fluorescence analysis with synchrotron radiation. European Journal of
> Mineralogy 21, 5, p. 927-945. Sorry for shameless advertising.
> The fluorescence from ordinary thin section glass swamped our Pb signal
> despite confocal arrangement of the experiment and caused an artefact
> and hence too high ages to be calculated. SiO2 glass did the trick
> for us, see figure6 below.
>
> cheers,
> Andreas
>
>
>> Dear Mike
>>
>> I was very interested by the paper with Sato that you sent to the
>> list on Dec. 31. Metamorphic temperatures of >1190 C are very
>> surprising in such rocks and if correct, would be quite important.
>> However, I think that the basis of this estimate is an analytical
>> error. The Ti compositions in quartz adjacent to rutile needles
>> shown in your Fig. 5 exactly match what John Fournelle has
>> calculated for the effect of secondary fluorescence of Ti X-rays by
>> bremsstrahlung, see below. It appears that the Ti content of this
>> quartz is actually very low in contrast to the UHT minerals of the
>> host rock; perhaps it was reset by unmixing of rutile needles.
>> John's calculations are described at:
>> http://www.geology.wisc.edu/~johnf/Ti-quartz.html
>>
>> We would be interested in your thoughts on this.
>>
>> I am copying this message to the list because many people are
>> interested and have already received the pdf of Sato and Santosh
>> (2007).
>>
>> Secondary fluorescence effects can extend further from a mineral
>> grain boundary than many people realize. This is especially
>> important to evaluate for trace element analysis.
>>
>> with best wishes, John
>>
>>
>>
>>
>>> Dear All,
>>>
>>> We had identified a similar occurrence as hematite from laser Raman
>>> study. Please see Fig. 2 (f,g) in the attached pdf file.
>>>
>>> Best wishes,
>>>
>>> Santosh
>>>
>>>
>>> ________________________________
>>>
>>> Prof. Dr. M. Santosh
>>>
>>> On sabbatical from:
>>> Faculty of Science
>>> Kochi University
>>> Kochi 780-8520
>>> JAPAN
>>>
>>> Editor-in-Chief
>>> Gondwana Research
>>> (www.elsevier.com/locate/gr)
>>>
>>> Content-Type: application/pdf; name="Sato and Santosh 2007 Min Mag.pdf"
>>> Content-Disposition: attachment;
>>> filename="Sato and Santosh 2007 Min Mag.pdf"
>>> X-Attachment-Id: f_g3v3wszk0
>>>
>>> Attachment converted: Macintosh HD:Sato and Santosh 200#4583D1.pdf
>>> (PDF /CARO) (004583D1)
>>
>>
>> --
>>> John W. Valley, phone: 608-263-5659
>>> Charles R. Van Hise Professor fax: 608-262-0693
>>> Dept. of Geoscience email: [log in to unmask]
>>> University of Wisconsin 1215 W. Dayton St.
>>> Madison, WI 53706, USA http://www.geology.wisc.edu/people/valley.html
>>>
>>> Zircons Are Forever- http://www.geology.wisc.edu/zircon/zircon_home.html
>>> Wisc-SIMS http://www.geology.wisc.edu/facilities/wiscsims/wisc_sims.html
>
>
> --
> --------------------------------
> Dr. Andreas Moeller
> Assistant Professor - Geochronology
> University of Kansas
> Department of Geology - IGL
> 2335 Irving Hill Road
> Nichols Hall, Room 243/357
> Lawrence, KS 66045-7559
> - USA -
>
> +1 (785) 864-1447 IGL Office (voicemail)
> +1 (785) 864-4846 Element2 Lab
> +1 (785) 864-5276 Fax
> [log in to unmask]
> http://www.geo.ku.edu/programs/tectonics/moller.shtml
--
Simon Harley FRSE
Professor of Lower Crustal Processes
Grant Institute of Earth Science
School of GeoSciences
University of Edinburgh
West Mains Road, Edinburgh, EH9 3JW
phone (0044) (0)131 650 4839
email [log in to unmask]
--
The University of Edinburgh is a charitable body, registered in
Scotland, with registration number SC005336.
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