Geochemical constraints on the model of the composition and thermal conditions of the Moon according to seismic data |
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| Authors: | O L Kuskov V A Kronrod |
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| Institution: | 1.Vernadsky Institute of Geochemistry and Analytical Chemistry,Russian Academy of Sciences,Moscow,Russia |
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| Abstract: | A new method of reconstruction of the temperature profile in the lunar mantle from the velocities of seismic P- and S-waves for different models of chemical composition is developed. The procedure of the solution of an inverse problem is realized
with the help of the minimization of the Gibbs free energy and the equations of state of a mantle substance, taking into account
phase transformations, anharmonicity, and the effects of inelasticity. The geophysical and geochemical constraints on composition
and temperature distribution in Moon’s mantle are established. The upper mantle can be composed of olivine pyroxenite, depleted
by low-volatile oxides (∼2 wt % of CaO and Al2O3). On the contrary, the lower mantle must be enriched by low-volatile oxides (∼4–6 wt % of CaO and Al2O3). Its composition can be represented by a mineral association of the olivine + clinopyroxene + garnet or olivine + orthopyroxene
+ clinopyroxene + garnet type, which is close in composition to pyrolite. The temperature distribution at depths 50–1000 km
are approximated by the equation: T(°C) = 351 + 17181–exp (−0.00082H)]. The constraints inferred make it possible to conclude that the published values of the velocities of P- and S-waves for the lunar mantle, obtained by processing the data of seismic experiments of the Apollo lunar mission are inconsistent
with each other at depths below 300 km. Otherwise, the variations in the velocities of P- and S-waves disturb the symmetry between the petrological model (composition), the temperature profile, and the seismic profile. |
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