Solubility of iron among plagioclase, clinopyroxene and silicate liquid in the system CaO-MgO-Al/sub 2/O/sub 3/ - SiO/sub 2/-Fe-O

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

OSTI ID:6169495

Virgo, D; Mysen, B O

The 1-atm liquidus of the system diopside-anorthite + 10wt% ferric iron is lower (approx. 30/sup 0/C) for end-member compositions but the temperature and projected (Fe-free) composition of the minimum melt are unchanged. The effect of fO/sub 2/ on the liquidus curve is minimal. The major element compositions, the structural state of iron and the ferrous/ferric ratio of existing crystal-liquid pairs have been determined using electron microprobe analyses and /sup 57/Fe Mossbauer spectroscopy. For anorthite-liquid pairs, the partition coefficient, D(Fe) (equal to (Fe in xtal)/(Fe in liquid)) decreases with increasing temperature and with increasing anorthite/diopside ratio, at fixed fO/sub 2/. The effect of bulk composition on D(Fe) predominates over the relatively weak temperature dependence (Longhi et al. 1976). Significantly, at fixed temperature and anorthite/diopside ratio, D(Fe) decreases linearly with fO/sub 2/ from 0.25 (log fO/sub 2/=-0.68) to 0.05 (log fO/sub 2/=-6.0). The increase in D(Fe) with increasing fO/sub 2/ is accompanied by an increase in the ferric iron content of the feldspar lattice. The mechanisms for incorporation of iron in synthetic anorthite are Fe(3+)-Al under oxidizing conditions and Fe(2+), Si-2Al under reducing conditions. The use of D(Fe) as an oxygen barometer is considered. D(Fe) for the system diopside-Fe/sub 2/O/sub 3/ is not strongly fO/sub 2/-dependent at constant temperature. The incorporation of iron in liquidus pyroxene is via the Fe(2+)-Ca substitution. Ferric iron acts as an inert diluent in these melts. Tschermak's substitution is discussed for igneous, ferric-bearing clinopyroxenes.

• Research Organization: Geophysical Laboratory, Washington, DC (USA)
• OSTI ID: 6169495
• 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)
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
ANORTHITE
CALCIUM COMPOUNDS
CALCIUM OXIDES
CHALCOGENIDES
CHEMICAL COMPOSITION
CHEMICAL REACTION KINETICS
CHEMISTRY
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DIOPSIDE
FELDSPARS
GEOCHEMISTRY
IRON COMPOUNDS
IRON OXIDES
KINETICS
MAGNESIUM COMPOUNDS
MAGNESIUM OXIDES
MINERALIZATION
MINERALS
OXIDES
OXYGEN COMPOUNDS
PYROXENES
REACTION KINETICS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SILICON OXIDES
SOLUBILITY
TRANSITION ELEMENT COMPOUNDS