Fundamental thermodynamic relations and silicate melting with implications for the constitution of D double prime

Journal Article · Sat Nov 10 00:00:00 EST 1990 · Journal of Geophysical Research; (United States)

OSTI ID:5195931

Stixrude, L; Bukowinski, M S.T. ^[1]

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1. Univ. of California, Berkeley (USA)

The authors describe fundamental thermodynamic relations (Helmholtz free energy as a function of volume and temperature) for solids and liquids, simple physically based expressions which contain all thermodynamic information about a system. The solid fundamental relation consists of Debye and Birch-Murnaghan finite-strain theory combined in the Mie-Grueneisen framework. The authors derive the liquid equation of state, which contains only four parameters, from the liquid fundamental relation and show that it successfully describes measurements of liquid alkali metals, water, and liquid diopside over a wide range of pressure and temperature. They find optimal fundamental relation parameters for diopside, enstatite, ilmenite, and perovskite and find the solid relation to be in excellent agreement with data, including heat capacities, thermal expansion, and MgSiO{sub 3} phase equilibria. They then combine the liquid and solid fundamental relations to calculate the melting curves of diopside, enstatite, and perovskite, which are found to be in excellent agreement with experiment. All predicted melting curves have dT/dP slopes which decrease steadily with pressure, eventually becoming negative because of liquid-crystal density inversion. The predicted melting temperature of perovskite in the D{double prime} region (3,750 K) at the base of the mantle is thousands of degrees lower than previous estimates, yet it is consistent with experimental data. By combining these results with seismic observations of the deep mantle, they propose that the D{double prime} layer consists of magnesiowuestite and silica in the form of stishovite or its recently discovered high-pressure modification.

• OSTI ID: 5195931
• Journal Information: Journal of Geophysical Research; (United States), Vol. 95:B12; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
EARTH MANTLE
CHEMICAL COMPOSITION
THERMODYNAMIC PROPERTIES
SILICATE MINERALS
MELTING
DIOPSIDE
ENSTATITE
EQUATIONS OF STATE
ILMENITE
LIQUIDS
MAGNESIUM COMPOUNDS
MAGNESIUM SILICATES
MELTING POINTS
PEROVSKITE
PHASE TRANSFORMATIONS
PLANETARY EVOLUTION
PRESSURE DEPENDENCE
SILICA
SOLIDS
SPECIFIC HEAT
TEMPERATURE DEPENDENCE
THERMAL EXPANSION
ALKALINE EARTH METAL COMPOUNDS
CHALCOGENIDES
EQUATIONS
EXPANSION
FLUIDS
MINERALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PEROVSKITES
PHYSICAL PROPERTIES
PYROXENES
SILICATES
SILICON COMPOUNDS
SILICON OXIDES
SOLAR SYSTEM EVOLUTION
TRANSITION TEMPERATURE
580000* - Geosciences