Activities and volumes in MgAl/sub 2/O/sub 4/ - Fe/sub 3/O/sub 4/ -. gamma. Fe/sub 8/3/O/sub 4/ spinels: implications for mantle oxygen fugacity

Conference · Tue Jan 01 04:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6193969

Mattioli, G S; Wood, B J

The partial molar volumes of Fe/sub 3/O/sub 4/ and ..gamma..Fe/sub 8/3/O/sub 4/ components in synthetic spinels have been determined by x-ray powder diffraction with wet chemical analysis of Fe/sup 2 +//Fe/sup 3 +/. These data, in addition to published results for the join Fe/sub 3/O/sub 4/-..gamma..Fe/sub 8/3/O/sub 4/, characterize the partial molar volumes within the ternary spinel system. Both the Fe/sub 3/O/sub 4/-..gamma..Fe/sub 8/3/O/sub 4/ and MgAl/sub 2/O/sub 4/-..gamma..Fe/sub 8/3O/sub 4/ joins show nearly linear molar volumes of mixing. The MgAl/sub 2/O/sub 4/-Fe/sub 3/O/sub 4/ join, however, shows a significant positive deviation from ideality, with volumes given by: V(cm/sup 3//mole) = 44.58 X/sub mt/ + 43.65 X/sub ..gamma..hm/ + 39.79 X/sub sp/ + 0.26 X/sub mt/X/sub sp/ (1) The effect of pressure on published intrinsic oxygen fugacity measurements of spinel separates from upper mantle xenoliths may now be assessed. Applying the authors partial molar volume data to reaction (2) yields a ..delta..V of 0.408 cal/bar. This would correspond to an absolute increase in oxygen fugacity of 203 log units at 30kb and 1000/sup 0/C, or a relative increase of 1-2 log units in fO/sub 2/ when compared to a pressure corrected IW buffer. The oxygen fugacities of spinel-lherzolite xenoliths may also be estimated from Fe/sub 3/O/sub 4/ activities in spinel, which have been determined using a zirconia solid electrolyte. Applying the authors experimental activity data to coexisting olivine (X/sub fa/=0.10), orthopyroxene (X/sub fs/=0.10), spinel (X/sub mt/=0.01) assemblages and correcting to 30kb and 1000/sup 0/C yields a value for log fO/sub 2/ of -9.2 or 0.5 log units below the QFM buffer. These new data bring the previously disparate methods of estimating upper mantle oxygen fugacity into 1-2 log units better agreement of 30kb.

• Research Organization: Northwestern Univ., Evanston, IL (USA)
• OSTI ID: 6193969
• Report Number(s): CONF-8510489-
• Conference Information: Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Journal Volume: 17
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580400* -- Geochemistry-- (-1989)
ACTIVATION ENERGY
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CHALCOGENIDES
CHEMICAL ANALYSIS
CHEMICAL REACTIONS
CHEMISTRY
COHERENT SCATTERING
DIFFRACTION
EARTH MANTLE
ELEMENTS
ENERGY
GEOCHEMISTRY
HYDROTHERMAL SYNTHESIS
IRON COMPOUNDS
IRON OXIDES
KINETICS
MAGMA
MAGMATISM
MAGNESIUM COMPOUNDS
MAGNESIUM OXIDES
MATERIALS
MINERALS
MIXING
NONMETALS
OXIDATION
OXIDE MINERALS
OXIDES
OXYGEN
OXYGEN COMPOUNDS
PRESSURE EFFECTS
QUANTITATIVE CHEMICAL ANALYSIS
REACTION KINETICS
SCATTERING
SPINELS
SYNTHESIS
SYNTHETIC MATERIALS
TRANSITION ELEMENT COMPOUNDS
VOLUMETRIC ANALYSIS
X-RAY DIFFRACTION