Hi Bob and others-
I did an empirical calibration of this geothermometer a long time ago. I basically used the grt-bt exchange data from Lang and Rice and made the approximation that the bt-chl Fe-Mg exchange from the same samples could be used to solve for the KD for grt-chl and the temperature. I think that it is referred to in the old Reviews in Mineralogy in the chapter by Jo Laird.
Ed Ghent
I have finally heard back from Dave Hewitt regarding the earlier question about the experimental calibration in the mid-80s (1986) of the T dependence of grt-chl Fe-Mg exchange that he did with Mel Dickenson. As far as I remember, this work appeared only as a GSA Abstract for the 99th Annual Meeting. Dave cannot find any notes regarding solution models they used at the time, and now thinks that they probably used a fairly simple ideal model - "nothing very sophisticated" in his words.
I have never been tempted to use this thermometer myself. Regardless of quality of experimental or theoretical geothermometer calibration, the tendency of chlorite to compositional re-equilibration down-temperature (and to common heterogeneity of chlorite compositions on a very local scale of micrometers) renders it of dubious value.
Bob T.
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Dr. Robert J. Tracy
Department of Geosciences
5064 Derring Hall
Virginia Tech
Blacksburg VA 24061-0420
Office Phone: 540-231-5980
Fax: 540-231-3386
