5:15 PM - 7:15 PM
[PPS08-P14] Reflectance spectroscopy using ilmenite and pyroxene/gabbro mixtures to estimate the distribution and abundance of ilmenite on the lunar surface
Keywords:Moon, ilmenite, reflectance spectra, laboratory spectroscopy
Ilmenite (FeTiO3) is enriched in basalt forming lunar mare and shows a wide composition variation by region on lunar surface. Ti, one of incompatible elements, is considered to reflect the chemical composition of the mantle during the formation of basaltic magma. Then, to clarify ilmenite distribution and abundance at the lunar surface is a key to elucidate the bulk composition which provide important information on the lunar magma ocean property.
Reflectance spectrum of ilmenite shows low visible (Vis)-near-infrared (NIR) reflectance, ultraviolet (UV) upturn, and a reflectance peak at around 950 nm between absorption bands of ~700 nm charge transfer between Ti3+ and Ti4+ and ~1200 nm Fe2+ crystal field transitions (Riner et al. 2009; Izawa et al. 2021; Robertson et al. 2022). Previous observations by Kaguya (SELENE) and ground telescopes obtained several lunar regions showing ~1000-nm peak, suggesting ilmenite-rich areas (e.g., Gaddis et al., 1985; Yamamoto et al., submitted). In addition, the UV-visible features obtained by spacecrafts have been used to estimate the TiO2 content of the lunar surface (e.g., Sato et al. 2017).
Ilmenite exists as a mixture with the other minerals on the lunar surface. Furthermore, mixture phase of ilmenite affects overall reflectance spectra in a non-linear way. Thus, the investigation of spectral changes in relation to ilmenite content provides significant insights into ilmenite distribution and abundance on the lunar surface. We in this study perform reflectance spectral measurements and bulk chemical analyses using pyroxene (pigeonite, augite) and gabbro powder samples. We use ilmenite powder samples mixed with pyroxene/gabbro to obtain lab UV-Vis-NIR spectra systematically. This allows us to understand the relationship between ilmenite content and spectral properties, i.e., reflectance, spectral slope, and absorption band depths.
Reflectance spectrum of ilmenite shows low visible (Vis)-near-infrared (NIR) reflectance, ultraviolet (UV) upturn, and a reflectance peak at around 950 nm between absorption bands of ~700 nm charge transfer between Ti3+ and Ti4+ and ~1200 nm Fe2+ crystal field transitions (Riner et al. 2009; Izawa et al. 2021; Robertson et al. 2022). Previous observations by Kaguya (SELENE) and ground telescopes obtained several lunar regions showing ~1000-nm peak, suggesting ilmenite-rich areas (e.g., Gaddis et al., 1985; Yamamoto et al., submitted). In addition, the UV-visible features obtained by spacecrafts have been used to estimate the TiO2 content of the lunar surface (e.g., Sato et al. 2017).
Ilmenite exists as a mixture with the other minerals on the lunar surface. Furthermore, mixture phase of ilmenite affects overall reflectance spectra in a non-linear way. Thus, the investigation of spectral changes in relation to ilmenite content provides significant insights into ilmenite distribution and abundance on the lunar surface. We in this study perform reflectance spectral measurements and bulk chemical analyses using pyroxene (pigeonite, augite) and gabbro powder samples. We use ilmenite powder samples mixed with pyroxene/gabbro to obtain lab UV-Vis-NIR spectra systematically. This allows us to understand the relationship between ilmenite content and spectral properties, i.e., reflectance, spectral slope, and absorption band depths.