DI43A-2610
Origin and Constraints on Ilmenite-rich Partial Melt in the Lunar Lower Mantle

Thursday, 17 December 2015
Poster Hall (Moscone South)
Ananya Mallik1, Heidi Fuqua2, Paul M Bremner3, Sanja Panovska4, Matthew R Diamond5, Simon James Lock6, Yasuhiro Nishikawa7, Hugo Jiménez-Pérez7, Anat Shahar8, Wendy R Panero9, Philippe Henri Lognonne7 and Ulrich Faul10, (1)Bayerisches Geoinstitut, Universitaet Bayreuth, Bayreuth, Germany, (2)University of California Berkeley, Berkeley, CA, United States, (3)University of Florida, Ft Walton Beach, FL, United States, (4)IGPP/SIO/UCSD, San Diego, CA, United States, (5)California Institute of Technology, Pasadena, CA, United States, (6)Harvard University, Cambridge, MA, United States, (7)Institut de Physique du Globe de Paris, Paris, France, (8)Carnegie Institution for Science Washington, Washington, DC, United States, (9)Ohio State University Main Campus, Columbus, OH, United States, (10)Massachusetts Institute of Technology, Cambridge, MA, United States
Abstract:
Existence of a partially molten layer at the lunar core-mantle boundary has been proposed to explain the lack of observed far-side deep moonquakes, the observation of reflected seismic phases from deep moonquakes, and the dissipation of tidal energy within the lunar interior [1,2]. However, subsequent models explored the possibility that dissipation due to elevated temperatures alone can explain the observed dissipation factor (Q) and tidal love numbers [3]. Using thermo-chemical and dynamic modeling (including models of the early lunar mantle convection), we explore the hypothesis that an ilmenite-rich layer forms below crustal anorthosite during lunar magma ocean crystallization and may sink to the base of the mantle to create a partial melt layer at the lunar core-mantle boundary. Self-consistent physical parameters (including gravity, pressure, density, VP and Vs) are forward calculated for a well-mixed mantle with uniform bulk composition versus a mantle with preserved mineralogical stratigraphy from lunar magma ocean crystallization. These parameters are compared against observed mass, moment of inertia, real and imaginary parts of the Love numbers, and seismic travel times to further limit the acceptable models for the Moon. We have performed a multi-step grid search with over twenty thousand forward calculations varying thicknesses of chemically/mineralogically distinct layers within the Moon to evaluate if a partially molten layer at the base of the lunar mantle is well-constrained by the observed data. Furthermore, dynamic mantle modeling was employed on the best-fit model versions to determine the survivability of a partially molten layer at the core-mantle boundary. This work was originally initiated at the CIDER 2014 program.

[1] Weber et al. (2011). Science 331(6015), 309–12.

[2] Khan et al. (2014). JGR 119.

[3] Nimmo et al. (2012). JGR 117, 1–11. 

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