Geophysical evidence for melt in the deep lunar interior and implications for lunar evolution

Citation:
Khan, A, Connolly JAD, Pommier A, Noir J.  2014.  Geophysical evidence for melt in the deep lunar interior and implications for lunar evolution. Journal of Geophysical Research-Planets. 119:2197-2221.

Date Published:

2014/10

Keywords:

anelasticity, chandler-wobble, data, density crossovers, electrical conductivity, electrical-conductivity, evolution, experimental constraints, geochemical constraints, magmatic evolution, mantle, mantle composition, moon, partial melt, polycrystalline olivine, seismic, structure, water-content

Abstract:

Analysis of lunar laser ranging and seismic data has yielded evidence that has been interpreted to indicate a molten zone in the lowermost mantle overlying a fluid core. Such a zone provides strong constraints on models of lunar thermal evolution. Here we determine thermochemical and physical structure of the deep Moon by inverting lunar geophysical data (mean mass and moment of inertia, tidal Love number, and electromagnetic sounding data) in combination with phase-equilibrium computations. Specifically, we assess whether a molten layer is required by the geophysical data. The main conclusion drawn from this study is that a region with high dissipation located deep within the Moon is required to explain the geophysical data. This region is located within the mantle where the solidus is crossed at a depth of approximate to 1200 km (1600 degrees C). Inverted compositions for the partially molten layer (150-200 km thick) are enriched in FeO and TiO2 relative to the surrounding mantle. The melt phase is neutrally buoyant at pressures of similar to 4.5-4.6 GPa but contains less TiO2 (<15 wt %) than the Ti-rich (similar to 16 wt %) melts that produced a set of high-density primitive lunar magmas (density of 3.4 g/cm(3)). Melt densities computed here range from 3.25 to 3.45 g/cm(3) bracketing the density of lunar magmas with moderate-to-high TiO2 contents. Our results are consistent with a model of lunar evolution in which the cumulate pile formed from crystallization of the magma ocean as it overturned, trapping heat-producing elements in the lower mantle.

Notes:

n/a

Website

DOI:

10.1002/2014je004661