title: Ancient igneous intrusions and early expansion of the Moon revealed by GRAIL gravity gradiometry.
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.
authors.affiliation: Department of Geophysics and Center for Space Resources, Colorado School of Mines, Golden, CO 80401, USA. jcahanna@mines.edu
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Andrews-Hanna
authors.forename: Sami W
authors.initials: SW
authors.lastname: Asmar
authors.forename: James W
authors.initials: JW
authors.lastname: Head
authors.forename: Walter S
authors.initials: WS
authors.lastname: Kiefer
authors.forename: Alexander S
authors.initials: AS
authors.lastname: Konopliv
authors.forename: Frank G
authors.initials: FG
authors.lastname: Lemoine
authors.forename: Isamu
authors.initials: I
authors.lastname: Matsuyama
authors.forename: Erwan
authors.initials: E
authors.lastname: Mazarico
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: McGovern
authors.forename: H Jay
authors.initials: HJ
authors.lastname: Melosh
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Neumann
authors.forename: Francis
authors.initials: F
authors.lastname: Nimmo
authors.forename: Roger J
authors.initials: RJ
authors.lastname: Phillips
authors.forename: David E
authors.initials: DE
authors.lastname: Smith
authors.forename: Sean C
authors.initials: SC
authors.lastname: Solomon
authors.forename: G Jeffrey
authors.initials: GJ
authors.lastname: Taylor
authors.forename: Mark A
authors.initials: MA
authors.lastname: Wieczorek
authors.forename: James G
authors.initials: JG
authors.lastname: Williams
authors.forename: Maria T
authors.initials: MT
authors.lastname: Zuber