¹Kevin Robertson,¹Ralph Milliken,¹Carle Pieters,¹Leif Tokle,¹Leah Cheek,¹Peter Isaacson
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114836]
¹Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI 02912 2, United States of America
Copyright Elsevier

The primary objective of this work is to constrain the physical and chemical effects of ilmenite on the spectral properties of high‑titanium lunar basalts. Here we use a combination of electron probe microanalysis, x-ray diffraction and VIS-NIR spectroscopy to characterize a suite of Apollo 17 High-Ti lunar basalts and a suite of synthetic laboratory derived binary mixtures to further understand the mixing systematics of opaque Fesingle bondTi oxides in a transparent silicate matrix. We demonstrate how the texture (particle size and shape) and composition (Fesingle bondMg content) of ilmenite exhibit strong controls over the spectral parameters of bulk basalts in the VIS-NIR wavelength range. We show that the presence of fine-grained ilmenite as opposed to coarse-grained ilmenite in high-Ti basalts causes suppression of pyroxene, olivine, and plagioclase absorption features, lowers reflectance values, and induces a stronger ‘red’ spectral slope at wavelengths >1.8 μm. These effects are considerably stronger for samples with fine-grained ilmenite crystals compared with coarse-grained samples that have similar ilmenite abundance. In addition, we show that minor variations in the Mg2+ content of ilmenite significantly alters the strength of the 1 μm feature and the slope above 1.8 μm, which similarly affects the spectral parameters of the bulk basalt. Our results indicate that lunar basalts with lower abundance of fine-grained ilmenite with slightly higher Mg content could exhibit a spectrum with an apparently stronger ilmenite signature when compared to basalts with more abundant, coarser ilmenite. Results presented here suggest that the accuracy of spectral mixing models of remotely sensed data on the Moon would improve by incorporating additional spectral end-members of ilmenite to better represent the compositional variability.

¹David Trang,¹Tyra Tonkham,²Justin Filiberto,¹Shuai Li,³Myriam Lemelin,⁴Catherine M.Elder
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114837]
¹Hawaiʻi Institute of Geophysics and Planetology, University of Hawaiʻi at Mānoa, Honolulu, Hawaiʻi, United States
²Lunar and Planetary Institute, USRA, Houston, TX, United States
³Département de Géomatique appliquée, Université de Sherbrooke, Québec, Canada
⁴Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States
Copyright Elsevier

Explosive volcanic eruptions are responsible for producing localized pyroclatic deposits found across the lunar surface. These small localized pyroclastic deposits are thought to have erupted through transient, vulcanian-like eruptions. We used several remote data products, including a water abundance map, to understand the compositional and physical properties of these pyroclastic deposits. Within these deposits, we found strong relationships between water abundance and pyroxene abundance, glass abundance, regolith density scale height, and longitude. These relationships suggest that water abundance can be used to estimate the gas content of an eruption, cooling rate of erupted pyroclasts, optical density of the eruption plume, degree of fragmentation of an eruption, and infer on the distribution of water in the lunar interior. Further, we deduce that the excess water abundance within these pyroclastic deposits represents interior water content, which we tied to other remote measurements that represent important petrological and volcanological parameters to understand eruption dynamics and behavior.