Magnetized magma intrusions being sources of a weak and a strong lunar magnetic anomaly revealed by 3D distribution of magnetization

In this work, we aim to investigate the origin of the magnetic carriers in the lunar crust and the intensity of the ancient dynamo field. The magnetization and depth range of magnetic carriers are studied under a weak and a strong magnetic anomaly in Mare Tranquillitatis and in Oceanus Procellarum, respectively, where the surface ages are 3.6 and 3.3 billion years. A sophisticated three-dimensional amplitude inversion software program from a geophysical survey is used to reconstruct the distributions of magnetization in the lunar crust. Because no globally measured surface magnetic field exists for the Moon, a crustal magnetic anomaly model with a grid resolution of 0.2° is used. The depth range of the magnetic source is fixed by the boundary identified by a relative criterion, which is 20% of the recovered maximum magnetization. The central burial depths of the magnetic carriers are approximately 15 km and 25 km under Reiner Gamma and Mare Tranquillitatis, respectively. The volumes of the two magnetic sources are at scales of 10⁴ and 10⁵ km³, respectively. The aforementioned differences may imply a hotter crust under Reiner Gamma than Mare Tranquillitatis by 3.3 billion years. The results support the view that the magma intrusions magnetized by an ancient magnetic field could be the origin of magnetic anomalies under Reiner Gamma and Mare Tranquillitatis. Compared with previous works, the maximum magnetization of 3 A/m under Reiner Gamma supports the intensity of the field being several microteslas.