Temperatures in the mantle as inferred from simple compositional models

This investigation tests the mixed-oxide model against the elastic and density requirements of the mantle within the region immediately below the 650 km discontinuity (approximately 650 to 1200 km). Mixed-oxide compositions containing combinations of (Mg.Fe)O and SiO/sub 2/ which correspond to dunite-peridotite and pyroxenite were emphasized in the modelling procedure. Models in the compositional range dunite-peridotite were found to satisfy the P and S-wave velocities, as well as the density requirements below the 650 km discontinuity; satisfactory solutions were provided by such models when Fe/(Mg + Fe) = 0.15 +- 0.05 along an adiabatic temperature gradient of 1300/sup 0/C at zero pressure. Models of pyroxenite composition do not satisfy the physical properties of the mantle in the region of interest. The successful dunite-peridotite mixed-oxide compositional models provide an estimate of the geotherm in the 650 to 1200 km region of the mantle. Since the physical properties within the region of interest are satisfied along an adiabat, the problem is reduced to calculating the increase of temperature with depth for the preferred model along the adiabatic gradient (initial temperature 1300/sup 0/C). This procedure yields a geotherm which is consistent with several independent upper mantle temperature estimates. The present results indicate amore » temperature of 1600 +- 400/sup 0/C at 671 km; the primary source of uncertainty is the accuracy of the seismic model interpretations.« less

[1]  Earl K. Graham.  Elasticity and Composition of the Upper Mantle , 1970 .

[2]  Murli H. Manghnani,et al.  Elastic constants of single‐crystal rutile under pressures to 7.5 kilobars , 1969 .

[3]  T. Ahrens.  The mineralogic distribution of iron in the upper mantle , 1972 .

[4]  A. Ringwood.  The chemical composition and origin of the Earth , 1966 .

[5]  E. K. Graham,et al.  The elastic constants of cassiterite SnO2 and their pressure and temperature dependence , 1975 .

[6]  E. Kröner,et al.  Elastic moduli of perfectly disordered composite materials , 1967 .

[7]  D. L. Anderson,et al.  Upper mantle structure of western North America from apparent velocities of P waves , 1965 .

[8]  G. McMechan,et al.  The Range of Earth Structure Non-uniqueness Implied by Body-Wave Observations , 1973 .

[9]  T. McGetchin,et al.  Compositional relations in minerals from kimberlite and related rocks in the Moses Rock dike, San Juan County, Utah , 1970 .

[10]  A. C. Victor,et al.  Thermodynamic Properties of Magnesium Oxide and Beryllium Oxide from 298 to 1,200 °K1 , 1963, Journal of research of the National Bureau of Standards. Section A, Physics and chemistry.

[11]  R. Hill.  The Elastic Behaviour of a Crystalline Aggregate , 1952 .

[12]  G. Davies,et al.  Limits on the Constitution of the Lower Mantle , 1974 .

[13]  F. Richter,et al.  Stability of a chemically layered mantle , 1974 .

[14]  Hitoshi Mizutani,et al.  Elastic‐wave velocities of polycrystalline stishovite , 1972 .

[15]  E. A. Flinn,et al.  Fine structure of the upper mantle , 1969 .

[16]  M. E. Striefler,et al.  Elastic and optical properties of stishovite , 1976 .

[17]  O. J. Kleppa,et al.  Thermodynamics of polymorphic transformations in silica. Thermal properties from 5 to 1070° K and pressure-temperature stability fields for coesite and stishovite , 1967 .

[18]  D. Anderson,et al.  Composition and evolution of the mantle and core. , 1971, Science.

[19]  Don L. Anderson,et al.  Application of isotropic finite strain theory to ultrasonic and seismological data , 1970 .

[20]  Don L. Anderson,et al.  Phase Changes in the Upper Mantle , 1967, Science.

[21]  O. Anderson,et al.  Pressure Derivatives of Elastic Constants of Single‐Crystal MgO at 23° and ‐195.8°C , 1966 .

[22]  Chi‐yuen Wang.  Temperature in the Lower Mantle , 1972 .

[23]  S. Nockolds.  AVERAGE CHEMICAL COMPOSITIONS OF SOME IGNEOUS ROCKS , 1954 .

[24]  D. Tozer.  The electrical properties of the earth's interior , 1959 .

[25]  Lane R. Johnson,et al.  Array measurements of P velocities in the upper mantle , 1967 .

[26]  Y. Syono,et al.  Melting of a peridotite nodule at high pressures and high water pressures , 1968 .

[27]  Don L. Anderson,et al.  The composition of the lower mantle , 1970 .

[28]  A. E. Ringwood,et al.  Mineral assemblages in a model mantle composition , 1963 .

[29]  Leon Thomsen,et al.  Elasticity of polycrystals and rocks , 1972 .

[30]  A. E. Ringwood,et al.  Density distribution and constitution of the mantle , 1964 .