The Ni-in-garnet geothermometer: calibration at natural abundances |
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| Authors: | Dante Canil |
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| Institution: | (1) School of Earth and Ocean Sciences, University of Victoria, PO Box 3055 3800 Finnerty Rd., Victoria V8W 3P6, Canada e-mail: dcanil@uvic.ca, CA |
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| Abstract: | Experiments to study the partitioning of Ni between olivine and garnet at natural abundances were performed at 1200 °C –
3 GPa, 1300 °C – 3, 5 and 7 GPa and 1500 °C – 5 GPa using piston-cylinder and multi-anvil apparatus. The experiments were
intended to provide a further test of the Ni-in-garnet geothermometer calibrated previously using enhanced Ni levels. The
run products were analysed by electron microprobe using special operating conditions to enhance counting statistics. Ni-Mg
and Fe-Mg exchange between olivine and garnet was tightly reversed. Results of the experiments suggest that Ni substitution
in garnet behaves according to Henry's Law up to levels of ∼3000 ppm. The Ni-in-garnet geothermometer derived from reversed
experiments in this study is consistent (within error) with that derived from previous experiments at enhanced levels of Ni;
neither of these experimental calibrations is consistent with any empirically derived Ni-in-garnet geothermometer. Sources
of the discrepancy between the empirical and experimental calibrations of the Ni-in-garnet geothermometer are examined in
detail and it is concluded that the main reason for the differences involves errors in the calculation of temperatures in
the empirical version. These errors are clearly demonstrated using a recently published data set for garnet peridotite xenoliths
in which both Ni-in-garnet and more conventional multi-equilibrium thermobarometry was employed.
Received: 25 August 1998 / Accepted: 10 March 1999 |
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