Research

Muscovite Barometry

Hopkins et al. (2008) translated mica composition into pressure using THERMOCALC, an internally consistent thermodynamic database (Holland and Powell, 1998) derived from relevant experimental studies. A possible limitation of their approach is that the input experimental results are limited to solid state studies in end-member systems such as K-feldspar+phlogopite+quartz (e.g., Massonne and Szpurka, 1997). Given the significance of the Hadean inclusion results, it is worthwhile to experimentally investigate celadonite exchange in the stability field of white micas to provide a direct calibration of Si/Al as a function of pressure, temperature, and magma composition. However, preliminary experiments at 7 kbars and 700°C using the Cootralantra granite (Chappell and White, 2004) as the starting composition yield only sub-mm sized muscovites, even for week-long heating durations. Seeding white micas in piston-cylinder runs and evaluating exchange progress provides some first order information, but to fully reverse these experiments requires the ability to undertake chemical characterization at the 100-nm-scale. Once our NanoSIMS analytical protocol is calibrated, we propose to undertake a systematic evaluation of the Si-in-muscovite barometer in a range of peraluminous melt compositions.

U-Th Partioning in Zircon Synthetic Zircon - PTX - UCLA

Matthew M. Wielicki

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