Geophysical evidence for melt in the deep lunar interior and implications for lunar evolution. Issue 10 (14th October 2014)

• Record Type: Journal Article
• Authors: Khan, A.; Connolly, J. A. D.; Pommier, A.; Noir, J.
• Is Part Of: Journal of geophysical research. Volume 119:Issue 10(2014:Oct.)
• Page Start: 2197
• Page End: 2221
• Publication Date: 2014-10-14
• Subjects: Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1002/2014JE004661
• Languages: English
• ISSNs: 2169-9097

Abstract

<abstract abstract-type="main" id="jgre20315-abs-0001"> <title>Abstract</title> <p id="jgre20315-para-0001">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 ∼1200 km (≥1600°C). Inverted compositions for the partially molten layer (150–200 km thick) are enriched in FeO and TiO<sub>2</sub> relative to the surrounding mantle. The melt phase is neutrally buoyant at pressures of ∼4.5–4.6 GPa but contains less TiO<sub>2</sub> (<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<sup>3</sup>). Melt densities computed here range from 3.25 to 3.45 g/cm<sup>3</sup> bracketing the density of lunar magmas with moderate‐to‐high TiO<sub>2</sub> 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.</p> </abstract>