Publication Date:
2014-09-19
Description:
. Analysis of lunar laser ranging and seismic data has yielded evidence that has been interpreted to indicate a molten zone in the lower-most mantle overlying a fluid core. Such a zone provides strong constraints on models of lunar thermal evolution. Here we determine thermo-chemical 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 1200 km (≥1600°C). Inverted compositions for the partially molten layer (150–200 km thick) are enriched in FeO and TiO 2 relative to the surrounding mantle. The melt phase is neutrally buoyant at pressures of ~4.5–4.6 GPa, but contains less TiO 2 (〈15 wt%) than the Ti-rich (~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 TiO 2 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.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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