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Neutral buoyancy of titanium-rich melts in the deep lunar interior

Nature Geoscience volume 5, pages 186–189 (2012)Cite this article

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Abstract

The absence of moonquakes originating deeper than about 1,100 km (ref. 1) implies that the lower mantle of the Moon could be partially molten. Up to 30% melt by volume has been estimated to exist between about 1,200 and 1,350 km depth2. However, the absence of recent volcanic activity at the Moon’s surface implies that such deep partial melts must be at least as dense as their surroundings. Here we use a combination of in situ synchrotron X-ray absorption techniques and molecular dynamics simulations to determine the density range of primitive lunar melts at pressures equivalent to those in the lunar interior. We find that only melts that contain about 16 wt% titanium dioxide are neutrally buoyant at depths corresponding to the top of the proposed partial melt zone. These titanium-rich melts are formed by deep partial melting of titanium-rich rocks. As such rocks are thought to have formed at shallow levels during crystallization of the lunar magma ocean, we infer that a significant vertical transport of mass occurred before melt formation. Our measurements therefore provide evidence for a large-scale overturn of the lunar mantle shortly after crystallization of the magma ocean and point to the continuing influence of a dense, titanium-rich reservoir on lunar interior evolution.

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Figure 1: Overview of experimental conditions and run products.
Figure 2: Lunar melt densities from molecular dynamics calculations and resulting equation of state (EOS) parameters.
Figure 3: Comparison of lunar-magma density measurements with the lunar-mantle density profile.

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Acknowledgements

This work was financially supported by a European Young Investigators award and Netherlands Space Office User Support Programme Space Research grant to W.v.W., and a European Research Council starting grant (FP7 grant agreement no. 259649) to C.S. We acknowledge the European Synchrotron Radiation Facility for provision of synchrotron radiation facilities and thank D. R. Neuville for carrying out 1-bar density measurements.

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Authors and Affiliations

  1. Faculty of Earth and Life Sciences, VU University Amsterdam, De Boelelaan 1085, 1081 HV, Amsterdam, The Netherlands

    Mirjam van Kan Parker, Elodie J. Tronche, Nachiketa Rai & Wim van Westrenen

  2. UPMC Université Paris 06, and CNRS, UMR 7193, Paris, France

    Chrystèle Sanloup

  3. SUPA, School of Physics and Astronomy, and Centre for Science at Extreme Conditions, University of Edinburgh, Edinburgh EH9 3JZ, UK

    Chrystèle Sanloup

  4. Laboratoire de Physique Théorique de la Matière Condensée (UMR7600), Université Pierre et Marie Curie (Paris 6), 4 Place Jussieu, 75252 Paris, France

    Nicolas Sator & Bertrand Guillot

  5. Laboratoire de Sciences de la Terre, Université de Lyon, UMR5570-CNRS-ENS Lyon-Université Claude Bernard Lyon 1, 2 Rue Raphaël Dubois, 69622 Villeurbanne, France

    Jean-Philippe Perrillat

  6. European Synchrotron Radiation Facility, 38043 Grenoble, France

    Mohamed Mezouar

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  1. Mirjam van Kan Parker
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Contributions

W.v.W., C.S. and M.v.K.P. devised the project. All authors participated in data acquisition. M.v.k.P., C.S., E.J.T., J-P.P., M.M., N.R. and W.v.W. carried out the in situ experiments. N.S. and B.G. carried out the computer simulations. W.v.W., M.v.K.P. and C.S. wrote the paper with input from all co-authors.

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Correspondence to Wim van Westrenen.

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The authors declare no competing financial interests.

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van Kan Parker, M., Sanloup, C., Sator, N. et al. Neutral buoyancy of titanium-rich melts in the deep lunar interior. Nature Geosci 5, 186–189 (2012). https://doi.org/10.1038/ngeo1402

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