Importance of considerations of mixing properties in establishing an internally consistent thermodynamic database: thermochemistry of minerals in the system Mg2SiO4-Fe2SiO4-SiO2

Sack, Richard O.; Ghiorso, Mark S.

doi:10.1007/bf01160190

Cited by 202 publications

(95 citation statements)

References 70 publications

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“…Given that peak temperatures (based on mineral abundances and textures) were not much higher than two-pyroxene closure temperatures, we can calculate the average Fa value corresponding to the two-pyroxene closure T and ƒO 2 . The resulting Fa value (5.2 mol%; Sack and Ghiorso, 1989) is only slightly above the average measured Fa value for these meteorites (4.7 mol%). Thus, winonaites and silicates in IAB irons experienced only slight reduction during cooling.…”

Section: Discussionmentioning

confidence: 86%

Thermodynamic constraints on the formation conditions of winonaites and silicate-bearing IAB irons

Benedix¹,

Лауретта²,

McCoy³

2005

Geochimica et Cosmochimica Acta

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Section: Discussionmentioning

confidence: 86%

Thermodynamic constraints on the formation conditions of winonaites and silicate-bearing IAB irons

Benedix¹,

Лауретта²,

McCoy³

2005

Geochimica et Cosmochimica Acta

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“…The silica activity of the liquid drops with pressure while the activities of MgO and FeO increase (Supplemental Fig. 1; Sack and Ghiorso, 1989;Hirschmann et al, 1998). Accordingly, the liquid in equilibrium with martian peridotites becomes enriched in olivine component as the pressure increases.…”

Section: Melting Behaviormentioning

confidence: 99%

Melting of the primitive martian mantle at 0.5–2.2 GPa and the origin of basalts and alkaline rocks on Mars

Collinet

Médard

Charlier

et al. 2015

Earth and Planetary Science Letters

109

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We have performed piston-cylinder experiments on a primitive martian mantle composition between 0.5 and 2.2 GPa and 1160 to 1550 • C. The composition of melts and residual minerals constrain the possible melting processes on Mars at 50 to 200 km depth under nominally anhydrous conditions. Silicate melts produced by low degrees of melting (<10 wt.%) were analyzed in layers of vitreous carbon spheres or in micro-cracks inside the graphite capsule. The total range of melt fractions investigated extends from 5 to 50 wt.%, and the liquids produced display variable SiO 2 (43.7-59.0 wt.%), MgO (5.3-18.6 wt.%) and Na 2 O + K 2 O (1.0-6.5 wt.%) contents. We provide a new equation to estimate the solidus temperature of the martian mantle: T ( • C) = 1033 + 168.1P (GPa) − 14.22P 2 (GPa), which places the solidus 50 • C below that of fertile terrestrial peridotites. Low-and high-degree melts are compared to martian alkaline rocks and basalts, respectively. We suggest that the parental melt of Adirondack-class basalts was produced by ∼25 wt.% melting of the primitive martian mantle at 1.5 GPa (∼135 km) and ∼1400 • C. Despite its brecciated nature, NWA 7034/7533 might be composed of material that initially crystallized from a primary melt produced by ∼10-30 wt.% melting at the same pressure. Other igneous rocks from Mars require mantle reservoirs with different CaO/Al 2 O 3 and FeO/MgO ratios or the action of fractional crystallization. Alkaline rocks can be derived from mantle sources with alkali contents (∼0.5 wt.%) similar to the primitive mantle.

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“…57, pp. Copyright the Mineralogical Society Petersen, 1977;Hackbarth and Petersen, 1984). These striking positive correlations between Sb/ (Sb + As) and Ag/(Ag + Cu) ratios reflect (1) As-Sb fractionation between hydrothermal fluids and fahlores, (2) coupling of the energies of element substitutions induced by incompatibilities between As and Ag, Zn and Ag, and Zn and As in the fahlore structure, and (3) nonidealities in the substitutions of Ag for Cu and As for Sb in fahlore (Sack, 1992). Values for the energies of the reciprocal reactions defining these incompatibilities, and for the energetic effects associated with the Ag for Cu and Zn for Fe exchange substitutions, have been established from constraints on exchange reactions between fahlores and assemblages consisting of simpler sulphosalts, sulphides, and alloys (cf.…”

Section: Introductionmentioning

confidence: 99%

As-Sb Exchange Energies in Tetrahedrite-Tennantite Fahlores and Bournonite-Seligmannite Solid Solutions

Sack

Ebel

1993

Mineral. mag.

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Reversed brackets on As and Sb partitioning between tetrahedrite-tennantite fahlores {--CUlo(Fe,Zn)2(Sb,As)4S13} and bournonite-seligmannite solid solutions {CuPb(Sb,As)S3} (400 ~ evacuated silica tubes, NH4CI flux) indicate that the maximum nonidealities associated with the As-Sb substitution are about 165 (bournonite) and 250 (fahlore) cal/gfw on a per atom exchange basis. The experimental constraints are consistent with the following calibration of the As-Sb exchange reaction between these phases: kcal/gfw, X2 -Zn/(Zn + Fe) (or one-half the number of Zn atoms/formula unit) and X3 -As/(As + Sb) refer to atomic ratios in fahlore, and AG~3-o = AH23 = 2.59 _+ 0.14 kcal/gfw (Raabe

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Importance of considerations of mixing properties in establishing an internally consistent thermodynamic database: thermochemistry of minerals in the system Mg2SiO4-Fe2SiO4-SiO2

Cited by 202 publications

References 70 publications

Thermodynamic constraints on the formation conditions of winonaites and silicate-bearing IAB irons

Thermodynamic constraints on the formation conditions of winonaites and silicate-bearing IAB irons

Melting of the primitive martian mantle at 0.5–2.2 GPa and the origin of basalts and alkaline rocks on Mars

As-Sb Exchange Energies in Tetrahedrite-Tennantite Fahlores and Bournonite-Seligmannite Solid Solutions

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