09:55 〜 10:10
[PPS09-04] Combined Orbiter and Surface Spectral Analyses of Olivine Exposure on the Moon
キーワード：月、SLIM、マントル、カンラン石
Previous remote-sensing data obtained by the SELENE (Kaguya) Spectral Profiler (SP) found exposures with olivine-rich spectral features, globally distributed on the lunar surface [1]. Their distributions surrounding large basins, their spectral characteristics indicating olivine-rich (pyroxene-poor) composition, and the distribution of the olivine-rich unit at fresh crater walls and ejecta suggest that these olivine-rich exposures possibly originated from the mantle that is excavated from depth by basin-forming impacts [1]. However, previous studies indicate that olivine-rich rocks on the Moon have three major origins: 1) mantle material, 2) olivine-rich volcanic material, and 3) olivine-bearing crustal intrusion (troctolite).
In this study, modal abundance of olivine, pyroxene, and plagioclase were estimated with Mg# of olivine and pyroxene by using spectral fitting developed by [2] to assess origin of the previously identified olivine exposures by [1] and to estimate Mg# of the lunar mantle. And we checked correlation between the estimated Mg# of olivine and diameter of crater/basin excavating each olivine exposure to understand chemical composition and vertical structure of the lunar interior. We used remote sensing reflectance spectra obtained by the SELENE (Kaguya) Spectral Profiler (SP) and Multiband Imager (MI) together with Multiband Camera [3] onboard Smart Lander for Investigating Moon (SLIM; SLIM is a technology demonstration mission to pinpoint landing within a hundred meters in radius).
Based on the estimated FeO abundance and Mg# of olivine from remote sensing spectra, there is a group having intermediate FeO abundance (5-10 wt.%) and higher Mg# (80-90) (group A), while in the same FeO range, some spectra having much lower Mg# (40-60) with a gap between the groups. In the lower FeO range (<5 wt.%), most of the data have Mg# ranging from 50 to ~80. Based on the FeO abundance and the higher Mg#, we interpreted that group A is possibly mantle origin. Correlation between crater/basin diameter of the location of olivine exposure and the estimated Mg# suggest that Mg# of olivine in the lunar interior deeper than a certain depth can be ~90 at maximum regardless of their origin (regardless of mantle olivine or olivine in crustal intrusion or lower crust). Therefore, regardless of their original, we need explanation for the common presence of high Mg# olivine (up to ~90) at depth. Spectra newly obtained by Multiband Camera at one of the olivine exposures will be combined to the orbiter spectra to further understand mineralogy and Mg# of this unique geologic unit.
[1] Yamamoto et al. (2010), Nature GeoSci. 3, 533-536. [2] Kato et al. (2018), 49th LPSC, abstract #1797. [3] Saiki et al. (2024), 55th LPSC, abstract#1801.
In this study, modal abundance of olivine, pyroxene, and plagioclase were estimated with Mg# of olivine and pyroxene by using spectral fitting developed by [2] to assess origin of the previously identified olivine exposures by [1] and to estimate Mg# of the lunar mantle. And we checked correlation between the estimated Mg# of olivine and diameter of crater/basin excavating each olivine exposure to understand chemical composition and vertical structure of the lunar interior. We used remote sensing reflectance spectra obtained by the SELENE (Kaguya) Spectral Profiler (SP) and Multiband Imager (MI) together with Multiband Camera [3] onboard Smart Lander for Investigating Moon (SLIM; SLIM is a technology demonstration mission to pinpoint landing within a hundred meters in radius).
Based on the estimated FeO abundance and Mg# of olivine from remote sensing spectra, there is a group having intermediate FeO abundance (5-10 wt.%) and higher Mg# (80-90) (group A), while in the same FeO range, some spectra having much lower Mg# (40-60) with a gap between the groups. In the lower FeO range (<5 wt.%), most of the data have Mg# ranging from 50 to ~80. Based on the FeO abundance and the higher Mg#, we interpreted that group A is possibly mantle origin. Correlation between crater/basin diameter of the location of olivine exposure and the estimated Mg# suggest that Mg# of olivine in the lunar interior deeper than a certain depth can be ~90 at maximum regardless of their origin (regardless of mantle olivine or olivine in crustal intrusion or lower crust). Therefore, regardless of their original, we need explanation for the common presence of high Mg# olivine (up to ~90) at depth. Spectra newly obtained by Multiband Camera at one of the olivine exposures will be combined to the orbiter spectra to further understand mineralogy and Mg# of this unique geologic unit.
[1] Yamamoto et al. (2010), Nature GeoSci. 3, 533-536. [2] Kato et al. (2018), 49th LPSC, abstract #1797. [3] Saiki et al. (2024), 55th LPSC, abstract#1801.