Depths to the Bottom and Volumes of Magnetic Sources under a Weak and a Strong Lunar Magnetic Anomaly Revealed by 3D Inversion

This work studies the remanent magnetization under a weak and a strong magnetic anomaly in Tranquillitatis and in Oceanus Procellarum respectively, which show similar surface ages of 3.6 Ga and 3.3 Ga. A 3D amplitude inversion is used to reconstruct the distributions of magnetization underground. Since there is no globally measured surface magneticeld for the Moon, a crustal magnetic anomaly model with grid resolution of 0.2° is used. The depth to the bottom of the magnetic source is fixed by the boundary identified by a relative criterion, which is 20% of the recovered maximum magnetization. The results show that the two anomalies have different depths to the bottom and different volumes of magnetic sources. The depth to the bottom of the magnetic carriers, which is possibly the Curie depth, is about 30 km and 50 km under Oceanus and Tranquillitatis. The volumes of the two magnetic sources are at the scale of 10⁴ and 10⁵ km³, respectively. The Bouguer gravity anomalies with spherical harmonics reaching 1200 degree in the two studied regions are also checked. The results supports that the magma intrusions containing different abundances of metallic iron are the most possible origins of the magnetic sources in the studied regions. Besides, the thermal states of lunar crust under the two studied maria were probably different during the acquisition process of remanent magnetization.