G33B-0953: GRAIL Gravity Observations of Lunar Volcanic Complexes

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Authors: Walter S Kiefer1, Maria T Zuber2, Patrick J McGovern1, James W Head3

Author Institutions: 1. Lunar and Planetary Institute, Houston, TX, USA; 2. Dept. Earth Atmospheric and Planetary Sciences, MIT, Cambridge, MA, USA; 3. Dept. Geological Sciences, Brown University, Providence, RI, USA

Team: GRAIL Science Team

Gravity observations by NASA’s GRAIL mission are providing important new insights into the volcanic plumbing associated with major volcanic complexes on the Moon. The Marius Hills are the Moon’s largest volcanic dome field, consisting of more than 250 basaltic domes and cones and 20 sinuous rilles. There are two distinct free-air gravity anomalies, with the larger anomaly (260 mGal) occurring close to the maximum concentration of volcanic domes in the northern part of the field. Much of the gravity anomaly in this area is due to buried, high density material, mapping out a sill complex with a spatial scale of 200 by 250 kilometers. For plausible choices of density contrast, the sill is more than 2 km thick in the north and 4 km thick in the south. The Aristarchus Plateau is the source for the Moon’s largest pyroclastic eruption and numerous sinuous rilles. Most of the gravity anomaly on the plateau itself has relatively low amplitude (< 60 mGal) and is likely due to isostatic or flexurally supported topography. There is a significant gravity high (160 mGal) associated with the Cobra Head, which is the source region for Vallis Schröteri, the largest rille in the Aristarchus Plateau. Regions of high free-air gravity also occur in the plains wrapping around the south and east sides of the plateau and in the adjacent Harbinger Mountains/Prinz Crater volcanic field (150 mGal). These gravity highs are all likely due to buried, high density material, plausibly in the form of volcanic intrusions. The Cauchy volcanic dome complex in eastern Mare Tranquillitatis is a regional topographic high about 400 km across but a free-air gravity low (-90 mGal). Similarly, the Hortensius/Tobias Mayer volcanic field in Mare Insularum is also a free-air gravity low (-80 mGal) in its center. In both cases, this implies the presence of low density material at depth, possibly due to thicker than normal crust. The Rümker Hills in northern Oceanus Procellarum is a small basaltic dome complex, 80 kilometers across, whose moderate free-air gravity anomaly (60 mGal) may be primarily due to its topography.