ORCID
https://orcid.org/0009-0002-1530-0455
Date of Award
12-17-2024
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
The Moon, our celestial satellite, has been a source of awe and inspiration persistent through the course of humankind’s existence. Scientific exploration of the Moon began with terrestrial observations, and since the dawning of the space age has accelerated alongside technological advancements. Analysis of lunar samples has marked the remarkable advancement of our knowledge of not just our Moon, but also the formation and evolution of Earth and planetary bodies. Beginning with the Apollo program, human exploration has returned samples from the Moon that allow sophisticated laboratory studies that led to the development of major theories in the field of planetary science, from the existence of global magma oceans to the giant impact hypothesis for Moon formation, as well as the pervasive nature of impact cratering and the establishment of cratering chronology models that have been applied to bodies across the solar system. We are now in the midst of a new era of lunar exploration, with the addition of robotic exploration and an ever-increasing collection of lunar meteorites. Many exciting scientific discoveries lie ahead with the Artemis program and missions to high-priority science targets discussed and proposed by lunar scientists in the decades since Apollo. However, the enhanced capabilities of our analytical instruments present a challenge in how to effectively wrangle and extract information out of the intimidating scale and amount of data that is collected. In my dissertation, I studied lunar volcanic samples with next-generation techniques developed in the decades since Apollo and demonstrated the capabilities of modern software and technology in quantitative sample analysis and scientific modeling. In chapter 2, I show that the clasts in lunar basaltic breccia meteorite Northwest Africa 12384 are similar to Apollo 12 and Apollo 15 low-Ti basalts, and that the basalt clasts are likely petrogenetically related to each other. However, crystallization modeling shows that a very low-Ti volcanic glass bead, also present in the meteorite, cannot be directly related to the basalt clasts, i.e., that the composition of the glass bead does not represent the direct parent magma of the basalts. These results suggest the existence of distinct, heterogeneous mantle source regions in Moon and perhaps the assimilation of a higher-Ti component during the evolution of the basaltic magma. During my study of this meteorite, I developed a process to analyze quantitative electron microprobe X-ray maps and accurately calculate bulk compositions of clasts using the Environment for Visualizing Images (ENVI®) (NV5 Geospatial) software. I had initially learned ENVI for remote sensing applications during my undergraduate career but realized that quantitative EPMA maps could be studied in the same way, effectively overcoming the challenge of how to view and extract statistics from millions of pixels that form a cube of chemical compositions. The ~3-billion-year radiometric age of the meteorite was determined through Pb-Pb secondary ion mass spectrometry and places the sample among a group of relatively younger, low-Ti lunar meteorites. In addition, I used the LROC QuickMap platform (https://quickmap.lroc.asu.edu/) to synthesize the information we had for NWA 12384 to hypothesize and constrain possible source regions of the meteorite on the Moon. In chapter 3, I present the first definitive extrusive sample of the lunar magnesian suite, a major crustal lithology of the Moon that formed post-lunar magma ocean. Until now, we had only observed intrusive, plutonic samples from the Apollo and meteorite collections of this rock type. As part of the Apollo Next Generation Sample Analysis Program, the Apollo 17 double-drive tube 73001/73002 was unsealed in 2019 and made available for scientific research for the first time, partly in preparation for the Artemis program. With the over-half-century advances in technology and analytical instrumentation, we were able to study the samples in the core to a degree that was unavailable to Apollo-era scientists. Non-destructive analysis with X-ray computed tomography at micron-scale voxel resolutions revealed a clast with an unusual texture compared to the known lunar sample collection. We requested a thick section of the clast, 73002,1017C, and showed with EPMA that the mineral chemistry was similar to samples of the Mg suite. Bulk compositional analysis with ENVI and subtraction of excess olivine showed a remarkable similarity to an unusual glass bead also found in the core. I collaborated with personnel at the NordSIMS facility at the Swedish Natural History Museum in Stockholm and performed analyses that led to the determination of a ~4.25-billion-year-old age for 73002,1017C. As this age is in the range of previously dated Mg-suite samples, it supports an origin as an extrusive member of the Mg-suite. To study the petrogenesis of this extrusive Mg-suite sample, I used the modeling software Perple_X and the Magma Chamber Simulator to show that the composition of 73002,1017C can be formed from the interaction between early mafic mantle melts and ferroan anorthositic crust. Furthermore, the liquid line of descent from the 73002,1017C composition may also lead to another lunar lithology, the mafic impact melt and melt breccias that were previously termed “low-K Fra Mauro basalts”. These “LKFM” basalts were a composition of basaltic impact glasses that were initially noted in Apollo 14 regolith, hence the name, but was found to be a component of regolith at other Apollo sites and thus surmised to be a major lunar crustal component. In chapter 4, I used ENVI to comb through continuous thin sections of 73001/73002 in search of volcanic glass. I located and extracted compositions of over 1500 glass beads and fragments and used discrimination diagrams and statistical analysis to compare them to other known lunar volcanic glasses. I show that the volcanic glass in 73001/73002 resemble those previously analyzed from other Apollo 17 sites, apart from the unusually high-Mg and high-Al glass that is related in some manner to the Mg-suite extrusive samples described in chapter 2. In addition, the identification of low- and moderate-Ti volcanic glass is much rarer than that of high-Ti glass, constituting around 2% of the total number of identified volcanic glasses, which is consistent with past studies of the Apollo 17 area. In chapter 5, I have written out a tutorial of methods used so future investigators can follow my methods step-by-step, whether it is ENVI quantitative EPMA map analysis, phase equilibria modeling, or scripts to facilitate data analysis and visualization. My hope is that researchers can use this chapter to effectively explore the incoming wealth of new lunar samples and sample data, thus contributing to - and building upon - our knowledge of lunar and planetary science. In this dissertation, the power of harnessing advancements across instrumentation, hardware, and software to approach large lunar scientific datasets is discussed. The effective use of quantitative EPMA maps through software and browser-based platforms is revolutionary for sample analysis, especially of precious samples where every milligram counts. The capabilities of modern computing power are shown through real-time manipulation of gigabytes of XCT and imagery data, as well as hours of phase-equilibria modeling. Rapid search and identification of clasts and fragments tens of microns to millimeters in scale with compositions of interest within a complex 50-centimeter regolith core is not only now possible, but it is straightforward given the right resources. The dissertation serves as a bridge between Apollo and Artemis, and heralds an exciting new era of lunar and planetary scientific exploration.
Language
English (en)
Chair and Committee
Bradley Jolliff
Committee Members
Michael Krawczynski; Rita Parai; Robert Dymek; Ryan Ogliore
Recommended Citation
Yen, Christopher, "Next-Generation Compositional and Chronological Sample Analysis of Lunar Low-Ti Basalts and Volcanic Glasses" (2024). Arts & Sciences Electronic Theses and Dissertations. 3376.
https://openscholarship.wustl.edu/art_sci_etds/3376