UC Santa Cruz

The goal of this thesis is to investigate the geologic origins of two different lunar magnetic anomalies: Reiner Gamma on the lunar nearside, and the Gerasimovich-area anomalies on the farside. Chapters 2 and 3 are concerned with Reiner Gamma, while Chapter 4 is concerned with the Gerasimovich-area anomalies. Understanding the geologic origins of these lunar magnetic anomalies is key to progressing our understanding of the Moon’s magnetic history, and this work carries out these investigations using data from lunar orbiters.In Chapter 2, I present evidence that the magnetic anomaly Reiner Gamma overlies a relative-negative Bouguer gravity anomaly. This gravity anomaly is likely a buried impact crater, and I determined its age, and thus the age of the Reiner Gamma magnetic source bodies, to be between ∼3.3 Ga and ∼3.9 Ga, which are the approximate temporal bounds of mare volcanism. This range of ages coincides with the putative high-field era of the lunar dynamo (∼3.56–3.9 Ga), thus, the high magnetization of Reiner Gamma could be due to deposition during a time of a high-magnitude ambient field. In Chapter 3, I present observations that a portion of Reiner Gamma appears to have been demagnetized by the emplacement of a dome in the nearby Marius Hills volcanic complex. I created three different models to determine if the observed magnetic anomaly was diminished by thermal demagnetization. First, I created a flexure model, which approximated the dome as a buried laccolith and determined the burial depth of the laccolith based on its surface expression. Second, I created a thermal model, which determined the time-temperature history of areas around the laccolith. Third, I created a dipole model that simulated thermal demagnetization via decreasing the moments of some of the source dipoles. These three models, taken together, suggest that thermal demagnetization did occur at Reiner Gamma, and we use this result to estimate source body burial depths of <∼2 km, age of ∼3.5-3.9 Ga, and a magnetization of ∼3.6 A/m. In Chapter 4, I present the observation that in the region of the Gerasimovich magnetic anomalies, areas of high magnetic field tend to overlie areas of low surface slope. Because the Gerasimovich region is antipodal to the Crisium basin, other work has suggested that the magnetic anomalies could be due to highly magnetic antipodal ejecta (Hood and Artemieva, 2008; Lin et al., 1988; Wakita et al., 2021). My work validates this antipodal ejecta hypothesis and estimates a magnetized layer thickness between ∼0.8-1.2 km and ∼2.4 km and a source body magnetization of ∼3-5 A/m.