Constraints on timing and magnitude of early global expansion of the Moon from topographic features in linear gravity anomaly areas

Abstract

Gravity data obtained from the Gravity Recovery and Interior Laboratory have revealed linear gravity anomalies (LGAs) formed by the early global expansion of the Moon and subsequent magma intrusion. In this study, using Lunar Orbiter Laser Altimeter topographic data, we investigated topographic profiles across LGAs to verify that they were formed by extensional tectonics. We found that 17 of the 20 LGAs investigated exhibited a valley structure, suggesting that they were formed by tensile stress. Assuming that these topographic depressions accompanied graben formation, the increase in the lunar radius is estimated to be on the order of several tens of meters. On the other hand, assuming that these topographic depressions accompanied flexure of elastic lithosphere due to the LGA load, the elastic thickness during the LGA formation is estimated as ~10 km. The crater frequencies in the vicinity of LGAs indicate that the peak tectonic activity occurred before the basin-forming epoch.