13:45 〜 14:00
[MIS18-01] かぐやMultiband Imagerを用いた月の火山ガラス堆積物の検出手法の開発
キーワード：リモートセンシング、月の火山、ダークマントル堆積物、可視近赤外分光観測
Over 100 lunar pyroclastic deposits (LPDs) have been identified. Several LPDs are known to consist of volcanic glass formed by rapidly quenched magma from the deep layer, which contains higher abundance of volatiles, therefore reflect important information about lunar interior volatiles. Previously, the distribution of glass-rich LPDs was limited to roughly a dozen large-scale regions (each covering an area of more than several thousand km2) (Gaddis et al., 1985), but recent local geological surveys from orbit using VIS-NIR spectroscopy have led to the discovery of over 10 additional glassy LPDs (e.g., Jawin et al., 2015; Gaddis et al., 2016; Farrand et al., 2022; 2023). We devised a method to detect glass-rich terrains using the Kaguya Multiband Imager (MI), which offers higher spatial resolution than the Moon Mineralogy Mapper used in previous studies, and conducted the first global survey of glassy LPDs.
Using data from the Kaguya Multiband Imager and the Chandrayaan-1 Moon Mineralogy Mapper, we proposed new parameters, the 1 um area width (1AW) and the 2 um band center (2BC), to identify the spectral features of Fe-bearing volcanic glass, as these materials exhibit a broader 1 um band and a short-wavelength shift of the 2 um band center. These parameters can identify regions meeting the thresholds of 1AW > 400 and 2BC < 2100 nm as glassy LPDs. We identified approximately 100 locations of glassy LPDs, more than half of which had not been previously recognized as such. Glassy LPDs are distributed widely across the lunar nearside as well as in several basins on the farside, and they appear to be relatively randomly distributed in regions where the crustal thickness is less than approximately 30 km.
At 62 of these locations, where volcanic vents could be identified, we measured the maximum dispersal range of the pyroclasts from the vent center using a threshold of 1AW = 400. Based on the pyroclast dispersal model of magma degassing and eruption proposed by Wilson and Head (2017), these glassy LPDs are suggested to have originated from source magmas containing several hundred to over a thousand ppm of volatiles, assuming that the source magma contained a mixture of CO and H2O as its volatile components. Our results imply that deep-sourced volcanic eruptions involving volatile-rich magmas were common throughout the Moon.
Using data from the Kaguya Multiband Imager and the Chandrayaan-1 Moon Mineralogy Mapper, we proposed new parameters, the 1 um area width (1AW) and the 2 um band center (2BC), to identify the spectral features of Fe-bearing volcanic glass, as these materials exhibit a broader 1 um band and a short-wavelength shift of the 2 um band center. These parameters can identify regions meeting the thresholds of 1AW > 400 and 2BC < 2100 nm as glassy LPDs. We identified approximately 100 locations of glassy LPDs, more than half of which had not been previously recognized as such. Glassy LPDs are distributed widely across the lunar nearside as well as in several basins on the farside, and they appear to be relatively randomly distributed in regions where the crustal thickness is less than approximately 30 km.
At 62 of these locations, where volcanic vents could be identified, we measured the maximum dispersal range of the pyroclasts from the vent center using a threshold of 1AW = 400. Based on the pyroclast dispersal model of magma degassing and eruption proposed by Wilson and Head (2017), these glassy LPDs are suggested to have originated from source magmas containing several hundred to over a thousand ppm of volatiles, assuming that the source magma contained a mixture of CO and H2O as its volatile components. Our results imply that deep-sourced volcanic eruptions involving volatile-rich magmas were common throughout the Moon.