Experimental investigation of Fe-Mg distribution between olivine and clinopyroxene: Implications for mixing properties of Fe-Mg in clinopyroxene and garnet-clinopyroxene thermometry
- Univ. of North Dakota, Grand Forks (United States)
- Univ. Blaise Pascal, Clermont-Ferrand (France)
Experiments conducted in a piston cylinder apparatus at 10.5 kbar, 1000 C, reveal that the exchange of Fe and Mg between olivine and clinopyroxene is nearly ideal. Fifty-three experimental half-reversals tightly constrain the curve ln K[sub d] vs. Fe/(Fe + Mg). If W[sub FaFo] = 4500 J/atom, the weighted least-squares regression of the experimental results yields W[sub HdDi] = 3978 [plus minus] 423 J/atom and [Delta]G[sub rxn][sup 0] = [minus]7208 [plus minus] 174 J/mol for the exchange reaction. A Monte Carlo regression yields similar results. Fe-Mg mixing in olivine, in the M1 site of clinopyroxene, in garnet, and in orthopyroxene can be characterized by small symmetrical Margules parameters: 4500, 3978, 1590, and 0 J/atom, respectively. Attempts to perform similar experiments of Fe-Mg exchange between garnet and clinopyroxene were unsuccessful. However, the olivine-clinopyroxene results can be combined with the results of other studies on Fe-Mg exchange between garnet and olivine to calculate a garnet-clinopyroxene thermometer. The calculated thermometer is highly uncertain but yields temperatures 30-190 C higher than those suggested by some recently published experimental results. One of the recent studies is likely in error; more experimental studies are needed to resolve the discrepancies.
- OSTI ID:
- 7006353
- Journal Information:
- American Mineralogist; (United States), Journal Name: American Mineralogist; (United States) Vol. 77:7-8; ISSN AMMIAY; ISSN 0003-004X
- Country of Publication:
- United States
- Language:
- English
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152004* -- Geothermal Data & Theory-- Isotope & Trace Element Studies
58 GEOSCIENCES
580000 -- Geosciences
BENCH-SCALE EXPERIMENTS
CALCULATION METHODS
CHEMICAL REACTIONS
GARNETS
GEOTHERMOMETERS
GEOTHERMOMETRY
LEAST SQUARE FIT
MAXIMUM-LIKELIHOOD FIT
MEASURING INSTRUMENTS
METAMORPHIC ROCKS
METAMORPHISM
MINERALS
MOLECULAR STRUCTURE
MONTE CARLO METHOD
NUMERICAL SOLUTION
OLIVINE
OXYGEN COMPOUNDS
PETROGENESIS
PROBABILITY
PYROXENES
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
STOCHASTIC PROCESSES
THERMOMETERS