Multi-disciplinary approach to constraining present-day internal structure of the Moon with implications for the evolution of the lunar interior
Abstract
The existence of a partially molten layer, deep within the Moon's mantle, has been proposed to explain the lack of observed far-side deep moonquakes, the observation of reflected phases from deep moonquakes, and the dissipation of tidal energy within the lunar interior. However, subsequent models have proposed that dissipation due to elevated temperatures alone can explain the observed dissipation factor and tidal love numbers. In this study we use thermo-chemical modeling to explore the hypothesis that an ilmenite-rich layer, formed just below crustal anorthosite during lunar magma ocean crystallization, may sink to the base of the mantle to create a partial melt layer at the lunar core-mantle boundary. We have performed over 200,000 forward calculations varying thicknesses of chemically and mineralogically distinct layers within the Moon to evaluate if an ilmenite-rich partially molten layer at the base of the lunar mantle is well constrained by the Apollo seismic data. Self-consistent physical parameters are calculated for three mantle compositional models: two well-mixed mantles with uniform bulk composition from [1] and [2], and a mantle with preserved mineralogical stratigraphy from magma ocean crystallization. Additionally, we considered a cold, medium, and hot selenotherm, or lunar temperature profile, for each compositional model. These parameters were compared against observed mass, moment of inertia (MOI), bulk chemistry, and seismic velocity profiles. We obtain the following key conclusions from our work: (1) the Moon must have a small (<400km) iron-rich core; (2) an overturn event likely occurred due to the lack of an ilmenite-rich layer preserved below the crust; (3) while the stratified chemistry models were able to meet the mass and MOI constraints for all three selenotherms, only the hot selenotherm was successful for the homogenous chemistry. We found that it is possible to reasonably fit the published seismic profiles with all three temperature profiles (cold, medium, and hot), however, mass and MOI place an additional key constraint. (Figure 1) for the Taylor Mean model classification, no models were found to adequately meet mass and MOI, despite fit to seismic profiles.
[1] Hauri, E. H., et al. (2015). EPSL, 409, 252-264. [2] Taylor, S. R. (1982). Phys. Earth & Planet. Int., 29(3-4), 233-241.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.P13B..06F
- Keywords:
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- 6250 Moon;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTSDE: 5464 Remote sensing;
- PLANETARY SCIENCES: SOLID SURFACE PLANETSDE: 5475 Tectonics;
- PLANETARY SCIENCES: SOLID SURFACE PLANETSDE: 5480 Volcanism;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS