Dear Ilya Bindeman,

I wonder if you have calculated the oxygen isotope temperature of
quartz-magnetite pairs from your zone tuffs by applying the experimental
calibration of Chiba et al. (1989). If yes, it is not surprised that the
higher isotope temperatures were obtained because the magnetite in their
thermometer is responsible for the spinel-type structure rather than the
inverse spinel-type structure (see Fig. 1 in Zheng Y.-F., 1995, Chem.
Geol., 121: 309-316). It appears that the magnatite in your samples is
of the inverse spinel-type structure since its crystallization.
Therefore, the theoretical calibration concerning the inverse
spinel-type magnetite (listed in Table 2 of Zheng, 1995) has to be
applied to your samples. I expect the nearly same temperatures as those
determined using the magnatite-ilmenite thermometer. Have you ever
measured the oxygen isotope composition of coexisting ilmenite? If yes,
you can do a test for the interal consistency.

Sincerely yours,
Yong-Fei Zheng


Ilya N. Bindeman wrote on April 2, 2000:
>
> Hello everybody,
>
> Is anyone aware of recent (after 1993) or current experiments on
> quartz-magnetite oxygen isotope fractionation?
> Will  the use of laser have a large advantage, given that magnetite is a
> difficult phase to react conventionally?
>
> When I apply Quartz-Magnetite oxygen isotope thermometers to different
> zoned tuffs (in order to determine the quenching temperature) and then
> compare it to the temperature determined using Magnetite-Ilmenite, I mostly
> discover that former (Quartz-Magnetite) temperature is often >100 C higher.
> There should be something systematically different in one of these methods.
> Analytical?
>
> Ilya Bindeman
> Research Associate
> Department of Geology and Geophysics
> University of Wisconsin
> 1215 W Dayton Str
> Madison WI 53706
> USA
>
> 608-262-7118
> [log in to unmask]
> http://geology.wisc.edu/~inbindem

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Dr. Yong-Fei Zheng
Professor and Chairman
Department of Earth and Space Sciences
University of Science and Technology of China
Hefei 230026, PR China
Tel.: (+86) 551 3603384        Fax: (+86) 551 3603554
Email: [log in to unmask]
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