Consequences and Resolution of Lunar Lower Mantle Partial Melt

Monday, 15 December 2014
Heidi Fuqua1, Paul M Bremner2, Matthew R Diamond1, Gordana Garapic3, Simon James Lock4, Ananya Mallik5, Yasuhiro Nishikawa6, Sanja Panovska7, Anat Shahar8, Philippe Henri Lognonne6, Wendy R Panero9, Ulrich Faul10, Mark P Panning2, Hugo Jimenez-Perez6, Nicholas C Schmerr11 and Quentin C Williams12, (1)University of California Berkeley, Berkeley, CA, United States, (2)Univ of FL-Geological Sciences, Gainesville, FL, United States, (3)SUNY College at New Paltz, Department of Geology, New Paltz, NY, United States, (4)Harvard Univ, Cambridge, MA, United States, (5)Rice University, Houston, TX, United States, (6)Institut de Physique du Globe de Paris, Paris, France, (7)IGPP/SIO/UCSD, San Diego, CA, United States, (8)Carnegie Institution of Washington, Geophysical Laboratory, Washington, DC, United States, (9)Ohio State University, Columbus, OH, United States, (10)Massachusetts Institute of Technology, Cambridge, MA, United States, (11)University of Maryland College Park, College Park, MD, United States, (12)University of California Santa Cruz, Santa Cruz, CA, United States
Existence of a partially molten layer at depth has been proposed to explain the lack of observed farside deep moonquakes, the observation of reflected phases from deep moonquakes, and the dissipation of tidal energy within the lunar interior. However, subsequent models explore the possibility that dissipation due to elevated temperatures alone can explain the observed dissipation factor (Q) and tidal love numbers. We have explored the hypothesis that high titanium melt compositions associated with lunar mantle overturn may sink to the base of the mantle, locally or regionally. We have performed forward calculations varying composition and thickness of layers to evaluate if a partially molten layer at the base of the mantle is well constrained by the observational data. Self-consistent physical parameters are calculated for each compositional model that are then compared against the observed data to determine a subset of permissible models. The data constraints considered by this study include bulk density, moment of inertia, real and imaginary parts of the Love numbers, seismic travel times, and electrical conductivity. Dynamic calculations using ASPECT have also been considered to determine the implications of early lunar mantle convection for the survivability of the partially molten layer. Finally, and as a perspective for a future NASA New Frontiers Geophysical Network, we present 1D synthetic seismograms calculated for each proposed structure of the Moon to investigate the future seismological resolution of these deep lunar structure features. This work was initiated at the CIDER 2014 program.