Gibbs-Duhem equation describes how T and P changes affect free energy (as chemical potential)

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Geothermobarametry

• Gibbs-Duhem equation describes how T and P
  changes affect free energy (as chemical potential)

Reaction with big DSR change a good barometer,
reaction with a big DVR change a good
thermometer.
Clausius-Clapeyron
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(No Transcript)
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Thermobarometry reactions

• Exchange Reactions - For solid solution series
  (Fe-Mg in olivine or pyroxene for example) T and
  P control the equilibrium distribution
• Solvus thermometry For minerals that exsolve, T
  at which 1 phase splits to 2 components dtermined
  by chemistry of the 2 components
• Trace element substitution into a certain mineral
  is T/P dependent (KD changes with T and P!)
• Isotope distributions in minerals are also T/P
  dependent

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Common thermometers
Exchange thermometers  
Minerals Elements
garnet-biotite Fe-Mg
garnet-cordierite Fe-Mg
garnet-clinopyroxene Fe-Mg
garnet-orthopyroxene Fe-Mg
garnet-hornblende Fe-Mg
garnet-olivine Fe-Mg
olivine-spinel Fe-Mg
two Fe-Ti oxides (e.g., ilmenite-magnetite) Fe-Ti
Minerals Elements
quartz-rutile Ti (in quartz)
zircon-rutile Ti (in zircon), Zr (in rutile)
hornblende-plagioclase Na-Ca
quartz-magnetite oxygen isotopic ratio
calcite-quartz, calcite-graphite carbon isotopic ratio
Solvus thermometers  
Minerals Elements
calcite-dolomite Ca-Mg
clinopyroxene-orthopyroxene Ca-Mg/Fe
plagioclase-alkali feldspar K-Na
muscovite-paragonite K-Na
monazite-xenotime Ce-Y
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Barometers
Net transfer barometers  
Assemblage Acronym(s)
garnet-Al2SiO5-quartz-plagioclase GASP, GPAQ
garnet-rutile-Al2SiO5-ilmenite-quartz GRAIL
garnet-rutile-ilmenite-plagioclase-quartz GRIPS
garnet-plagioclase-muscovite-biotite GPMB
garnet-plagioclase-hornblende-quartz GPHQ
garnet-plagioclase-orthopyroxene-quartz  
garnet-plagioclase-clinopyroxene-quartz  
garnet-omphacite-kyanite-quartz/coesite (/- phengite)  
K-feldspar-jadeite-quartz  
garnet-cordierite-sillimanite-quartz  
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Garnet-Plagioclase-Kyanite-Quartz barometer
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Garnet-Biotite Geothermometer

• From Selverstone,
• http//serc.carleton.edu/files/NAGTWorkshops/petro
  logy/teaching_examples/Selverstone_thermobarometry
  .pdf