Foundations of Lunar Highland Crustal Mineralogy Derived from Remote Sensing and Laboratory Spectroscopy of Plagioclase-Dominated Materials

Cheek, Leah

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Year:: 2014
Contributor:: Cheek, Leah (creator); Pieters, Carle (Director); Mustard, John (Reader); Parman, Stephen (Reader); Cooper, Reid (Reader); Jolliff, Bradley (Reader); Brown University. Geological Sciences (sponsor)
Genre:: theses
Subject:: Moon; Spectroscopy; Plagioclase; Anorthosite; Geology
Extent:: xiii, 287 p.
DOI: https://doi.org/10.7301/Z0BP015Q

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Abstract:: Recent data from orbital spectrometers at the Moon have, for the first time, directly identified the mineral structure of plagioclase feldspar on the lunar surface. This detection is significant because it enables robust mineralogic investigations of the Moon’s most ancient, primary crust, which is dominated by plagioclase. This thesis is directed at (1) determining what information can be extracted from spectra of plagioclase-bearing materials in terms of mineral composition and abundance, and (2) applying these lessons to interpretation of new spectroscopic data at two case study locations on the Moon. The fist goal is accomplished through detailed spectroscopic investigations of well-characterized plagioclase and plagioclase-dominated materials in a laboratory setting. In Chapter 1, we begin with an analysis of plagioclase and anorthosite samples from a diversity of origins: terrestrial, lunar, and synthetic. In Chapter 2, we explore the variations in bulk spectral properties that arise from systematic percent-level changes in the minor mafic component in analog anorthosite materials. From these two laboratory-based chapters, we find that the plagioclase absorption is repeatable for a range of different sample compositions and geologic histories. Furthermore, the addition of small amounts of different mafic components enables estimation of mineral abundances in the bulk sample rather than simply erasing the plagioclase feature. In Chapter 3, we analyze nearly 800 anorthosite exposures across the ~1000 km diameter Orientale basin and find that most occurrences are exceedingly pure, containing >95%, and often >98%, plagioclase. A similar investigation at the smaller (~200 km diameter) Tsiolkovskiy crater in Chapter 4 shows much more variability in the anorthosite purity over relatively small (hundred-meter) spatial scales. The contrast between the anorthositic exposures at these two locations, coupled with the laboratory data that enable estimation of their mineral make-up, suggests that the structure of the Moon’s anorthositic crust, which has often been considered generically “plagioclase-rich”, contains vertical and/or lateral heterogeneity that is quantifiable using new remote sensing data. This new view of the Moon provides crucial information on the fundamental geologic constraints that guided lunar formation and evolution – from magma ocean crystallization mechanics to bulk crustal composition.
Notes:: Thesis (Ph.D. -- Brown University (2014)

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Cheek, Leah, "Foundations of Lunar Highland Crustal Mineralogy Derived from Remote Sensing and Laboratory Spectroscopy of Plagioclase-Dominated Materials" (2014). Earth, Environmental and Planetary Sciences Theses and Dissertations. Brown Digital Repository. Brown University Library. https://doi.org/10.7301/Z0BP015Q

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Earth, Environmental and Planetary Sciences Theses and Dissertations

Theses and Dissertations for the Earth, Environmental and Planetary Sciences department.
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