Dissipation at tidal and seismic frequencies in a melt-free Moon

Abstract

We calculate viscoelastic dissipation in the Moon using a rheological (extended Burgers) model based on laboratory deformation of melt-free polycrystalline olivine. Lunar temperature structures are calculated assuming steady state conduction with variable internal heat production and core heat flux. Successful models can reproduce the dissipation factor (Q) measured at both tidal and seismic frequencies, and the tidal Love numbers h2 and k2, without requiring any mantle melting. However, the frequency-dependence of our model Q at tidal periods has the opposite sign to that observed. Using the apparently unrelaxed nature of the core-mantle boundary (CMB), the best fit models require mantle grain sizes of ̃1 cm and CMB temperatures of ̃1700 K. If melt or volatiles are present, the lunar temperature structure must be colder than our melt-free models. We estimate a present-day mantle heat production rate of 9-10 nWm-3, suggesting that roughly half of the Moon's radiogenic elements are in the crust. © 2012. American Geophysical Union. All Rights Reserved.