Charge balancing of trivalent trace elements in olivine and low-Ca pyroxene: A test using experimental partitioning data

Journal Article · Wed Mar 01 00:00:00 EST 1989 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(89)90007-0· OSTI ID:5098040

Colson, R O; Taylor, L A ^[1]; McKay, G A ^[2]

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1. Univ. of Tennessee, Knoxville (USA)
2. NASA Johnson Space Center, Houston, TX (USA)

Charge-balancing substitution mechanisms have been determined for the incorporation of the trivalent cations Al and Sc in low-Ca pyroxene and Al, Sc, Yb, and Cr in olivine. In low-Ca pyroxene, the substitution mechanism was determined by evaluating covariations of trivalent trace cations with Si, Mg, Fe, and Ca. In olivine, substitution mechanisms were determined by comparison of the observed compositional dependence of partitioning to the compositional dependence theoretically expected for each substitution reaction. In low-Ca pyroxene, both cations investigated (Al{sub VI} and Sc{sub VI}) are charge balanced by the coupled substitution of Al for Si in tetrahedral sites. In olivine, the smaller cations (Al{sub VI} and Cr{sup +3}{sub VI}) are charge balanced in part of this same substitution (Al {leftrightarrow} Si){sub VI}. However, the larger cations (Sc{sub VI}, Yb{sub VI}) are charge balanced by a vacancy substitution: 2 (M{sup +3}){sub VI} + vacancy{sub VI} {leftrightarrow} 3 (M{sup +2}){sub VI}. The vacancy substitution is also important in charge balancing Al in olivine. These observations are important in establishing the mineral-melt reactions needed to construct the appropriate equilibrium constant for the partitioning reactions among melt, olivine, and low-Ca pyroxene. The correct equilibrium constant constrains the compositional dependence of trace element partitioning and thereby permits improved modeling of magma evolution.

• OSTI ID: 5098040
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Vol. 53:3; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
OLIVINE
CHARGE EXCHANGE
IONIC COMPOSITION
PYROXENES
ALUMINIUM IONS
CHEMICAL COMPOSITION
CHROMIUM
EQUILIBRIUM
GEOCHEMISTRY
MAGMA
MINERALIZATION
SCANDIUM IONS
TRACE AMOUNTS
VALENCE
YTTERBIUM
ALKALINE EARTH METAL COMPOUNDS
CHARGED PARTICLES
CHEMISTRY
ELEMENTS
IONS
IRON COMPOUNDS
IRON SILICATES
MAGNESIUM COMPOUNDS
MAGNESIUM SILICATES
METALS
MINERALS
OXYGEN COMPOUNDS
RARE EARTHS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
580000* - Geosciences