講演情報
[PPS02-P23]Field Study of Lunar Analog Volcanism Using a Handheld Gamma-Ray Neutron Spectrometer at the San Francisco Volcanic Field, Arizona
*Deniz Olcek1,2,3、Craig Hardgrove2、Thomas Prettyman4、Amber L. Gullikson5、Kerri L. Donaldson Hanna6、Kristen A. Bennett7、Margaret Landis2、Lena Heffern8 (1.Centre for Space Sensors and Systems (CENSSS), Institute of Technology Systems (ITS), University of Oslo, Gunnar Randers vei 19, 2007 Kjeller, Norway、2.Arizona State University (ASU), School of Earth and Space Exploration (SESE), 781 Terrace Mall, Tempe, AZ 85287, USA、3.EIDEL AS, Sørumsgata 5, 2000 Lillestrøm, Norway、4.Planetary Science Institute (PSI), 1700 E Fort Lowell Rd STE 106, Tucson, AZ 85719, USA、5.US Geological Survey (USGS), 2255 N Gemini Rd, Flagstaff, AZ 86001, USA、6.University of Central Florida (UCF), Deparment of Physics, 4111 Libra Drive, Orlando, FL 32816, USA、7.Northern Arizona University (NAU), 525 S. Beaver St., 4th Floor Flagstaff AZ 86011, USA、8.AstraNext, 1233 Cottonwood St, Broomfield, CO 80020, USA)
キーワード：
analog field study、lunar surface exploration、gamma-ray spectroscopy、lunar volcanism
Lunar silicic volcanism provides key constraints on the Moon’s crustal evolution, magmatic differentiation, and volcanic history. The Lunar-VISE (Lunar Vulkan Imaging and Spectroscopy Explorer) mission will investigate the Gruithuisen Domes—hypothesized products of silicic volcanism—through in situ lunar surface exploration aimed at constraining their composition, formation processes, and geologic evolution. As part of the payload, the Lunar-VISE gamma-ray and neutron spectrometer (LV-GRNS) will enable geochemical characterization by measuring K, Th, and U (and associated decay products), which serve as diagnostic tracers of evolved lithologies and crustal differentiation.
In preparation for Lunar-VISE, we conducted preliminary fieldwork with a portable gamma-ray neutron detector across compositionally diverse volcanic centers in the San Francisco Volcanic Field (SFVF) near Flagstaff, Arizona, including the rhyolitic silicic dome of Sugarloaf Mountain and basaltic terrains at Bonito Lava Flow and Robinson Mountain. Site-averaged radioisotope concentrations derived from gamma-ray spectroscopy show strong contrasts consistent with magmatic differentiation: Sugarloaf exhibits elevated mean K, U, and Th (K = 3.29 +/- 0.24 wt%, U = 14.35 +/- 1.81 ppm, Th = 27.14 +/- 2.43 ppm) compared to basaltic sites (Bonito: K = 1.13 +/- 0.08 wt%, U = 3.86 +/- 0.52 ppm, Th = 7.52 +/- 1.02 ppm; Robinson: K = 1.46 +/- 0.16 wt%, U = 5.59 +/- 1.06 ppm, Th = 11.75 +/- 1.98 ppm). Correspondingly, gamma-ray fluxes at Sugarloaf are higher by a factor of ~3-5 than nearby basaltic terrains.
To assess field performance and rover-relevant proximity effects, we conducted a series of incremental measurement stops while approaching Th-enriched cliff faces. Within rhyolitic sites, derived Th concentrations increase by ~10–30% at meter-scale standoff distances, indicating localized compositional heterogeneity and highlighting the sensitivity of GRNS measurements to measurement geometry. Overall, these results show that portable GRNS can resolve both regional contrasts and meter-scale variability in silicic analog terrains, providing field-tested guidance for optimizing LV-GRNS measurement strategies for exploration of the Gruithuisen Domes and other rover-based planetary missions.
In preparation for Lunar-VISE, we conducted preliminary fieldwork with a portable gamma-ray neutron detector across compositionally diverse volcanic centers in the San Francisco Volcanic Field (SFVF) near Flagstaff, Arizona, including the rhyolitic silicic dome of Sugarloaf Mountain and basaltic terrains at Bonito Lava Flow and Robinson Mountain. Site-averaged radioisotope concentrations derived from gamma-ray spectroscopy show strong contrasts consistent with magmatic differentiation: Sugarloaf exhibits elevated mean K, U, and Th (K = 3.29 +/- 0.24 wt%, U = 14.35 +/- 1.81 ppm, Th = 27.14 +/- 2.43 ppm) compared to basaltic sites (Bonito: K = 1.13 +/- 0.08 wt%, U = 3.86 +/- 0.52 ppm, Th = 7.52 +/- 1.02 ppm; Robinson: K = 1.46 +/- 0.16 wt%, U = 5.59 +/- 1.06 ppm, Th = 11.75 +/- 1.98 ppm). Correspondingly, gamma-ray fluxes at Sugarloaf are higher by a factor of ~3-5 than nearby basaltic terrains.
To assess field performance and rover-relevant proximity effects, we conducted a series of incremental measurement stops while approaching Th-enriched cliff faces. Within rhyolitic sites, derived Th concentrations increase by ~10–30% at meter-scale standoff distances, indicating localized compositional heterogeneity and highlighting the sensitivity of GRNS measurements to measurement geometry. Overall, these results show that portable GRNS can resolve both regional contrasts and meter-scale variability in silicic analog terrains, providing field-tested guidance for optimizing LV-GRNS measurement strategies for exploration of the Gruithuisen Domes and other rover-based planetary missions.