Investigation into Igneous Lithologies and Impact Processes in the Earth-Moon System

Abstract

In this dissertation, I work to characterize igneous lithologies and understand how impact processes produce and alter material on rocky surfaces. I investigate these topics to answer long-standing questions about volcanism and impact cratering on the Moon. I identify two new basalt types from the Moon: a potentially young, Th-enriched mare basalt from the previously unsampled region of the Moon, western Oceanus Procellarum; and evidence for an Mg-rich, spinel-bearing basalt that may represent extrusive Mg-suite magmatism. For the mare basalt, I conducted petrologic experiments that showed the sample is representative of the lava flow it originated from and showed that the sample likely underwent a late-stage, enigmatic processes known as silicate liquid immiscibility. We provide hypotheses for the provenance of this sample. The Mg-rich samples occur as clasts, some of which we determine to be of impact melt origin. However, a subset of the clasts have very similar texture and mineral chemistry. We propose that this subset of clasts may be volcanic in origin, and call for further investigations of these samples. The samples in both of these studies were impact-modified. The former came from a soil sample, likely delivered to the Apollo 12 site by a young impact event. The latter involves clasts embedded in an impact melt breccia. For the final portion of my dissertation, I characterize a polymict, impact melt-bearing rock (known as suevite) from Ries Crater in Germany to constrain the pressures and temperatures involved informing such a rock and constrain formation mechanisms. I identify zircon grains that have experienced a variety of pressure and temperature conditions, ranging from unshocked and unheated, to highly shocked, to heated, to both highly shocked and heated. The diversity of grains identified in this single sample provide insights into the formation of the suevite as a lateral flow. This terrestrial study is crucial to better understanding the impact cratering process, which produces knowledge that can be extended to more heavily impacted surfaces like the Moon’s. All of these studies, of impact altered rocks, of new igneous lithologies, and of impact cratering effects on target material, combine to set the stage for upcoming sample return missions from the Moon. The proposed Artemis missions, return humans to the Moon, will land near the lunar south pole, a heavily cratered and ancient surface. This dissertation lays some of the groundwork on how to best characterize the impact modified samples likely to be returned from the Moon. I have structured the document to begin with an introduction to lunar science and lunar rocks, followed by a description of the methods I used to conduct my research. Next, I will discuss the Th-enriched mare basalt found at Apollo 12, the Apollo 16 samples that may represent extrusive Mg-suite magmatism, and an investigation of pressures and temperatures recorded zircons in a sample from Ries Crater, Germany. Finally, I will close with a brief summary of my findings, their implications, and potential directions for future research.