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Ancient Igneous Intrusions and Early Expansion of the Moon Revealed by GRAIL Gravity Gradiometry
J. C. Andrews‐Hanna (Colorado School of Mines), S. W. Asmar (Jet Propulsion Laboratory), James W. Head III (Brown University), Walter S. Kiefer (Lunar and Planetary Institute), Alex S. Konopliv (Jet Propulsion Laboratory), F. G. Lemoine (Goddard Space Flight Center), I. Matsuyama (University of Arizona), E. Mazarico (Goddard Space Flight Center, Massachusetts Institute of Technology), Patrick J. McGovern (Lunar and Planetary Institute), H. J. Melosh (Purdue University West Lafayette), Gregory A. Neumann (Goddard Space Flight Center), F. Nimmo (University of California, Santa Cruz), Roger J. Phillips (Southwest Research Institute), David E. Smith (Massachusetts Institute of Technology), Sean C. Solomon (Lamont-Doherty Earth Observatory, Carnegie Institution for Science), G. Jeffrey Taylor (University of Hawaiʻi at Mānoa, University of Hawaii System), Mark A. Wieczorek (Institut de physique du globe de Paris, Sorbonne Paris Cité), James Gordon Williams (Jet Propulsion Laboratory), Maria T. Zuber (Massachusetts Institute of Technology)
Abstract: The earliest history of the Moon is poorly preserved in the surface geologic record due to the high flux of impactors, but aspects of that history may be preserved in subsurface structures. Application of gravity gradiometry to observations by the Gravity Recovery and Interior Laboratory (GRAIL) mission results in the identification of a population of linear gravity anomalies with lengths of hundreds of kilometers. Inversion of the gravity anomalies indicates elongated positive-density anomalies that are interpreted to be ancient vertical tabular intrusions or dikes formed by magmatism in combination with extension of the lithosphere. Crosscutting relationships support a pre-Nectarian to Nectarian age, preceding the end of the heavy bombardment of the Moon. The distribution, orientation, and dimensions of the intrusions indicate a globally isotropic extensional stress state arising from an increase in the Moon's radius by 0.6 to 4.9 kilometers early in lunar history, consistent with predictions of thermal models.