Compton-Belkovich Volcanic Complex As An Exploration Destination
Overview and Science: Silicic (or felsic) nonmare volcanism on the Moon has been confirmed by LRO Diviner data [1-3], including new occurrences associated with exposures of evolved silicic rocks at Aristarchus Crater and the nearby Aristarchus Plateau [4,5]. The associated style of volcanism is quite variable and has been detailed at numerous locations within the Procellarum KREEP Terrane (PKT). The origins of these felsic volcanic complexes and materials on the Moon are poorly understood and represent one of the enduring problems of lunar petrology, geochemistry, and geology. One of the more enigmatic landforms on the Moon is the Compton-Belkovich Volcanic Complex (CBVC) [3,6,7], which occurs outside of the PKT at 99.5 °E and 61.1°N, and which was first recognized as a prominent and highly focused Th-rich anomaly in Lunar Prospector gamma ray data . LRO Narrow Angle Camera (NAC) data revealed a small, 2535 km, well-preserved (with respect to other more heavily cratered terrains) volcanic complex associated with this anomaly. The volcanic complex has high visible-light reflectance for the Moon, consistent with its silica-rich composition , and consistent with a strong Diviner signal for silica enrichment . Moreover, Moon Mineralogy Mapper data suggest the presence of a strong OH feature at the CBVC [9,10], possibly related to silicic pyroclastic activity . Impact crater size-frequency data indicate an age of about 3.5 Ga . Although the site is technically on the lunar farside and located at a far northerly latitude, once farside communications infrastructure becomes available, the CBVC should be considered a high science priority site for in-situ investigation using a mobile analytical platform. A single collection site for sample return might miss important lithologic diversity. Although astronauts would be the ultimate explorers at this location, key science objectives could be met with a rover mission. Terrain and Landing sites. The CBVC comprises a broad, low dome with an irregularly shaped central depression that has been interpreted as a volcanic caldera. Superimposed on the broad dome are several relatively large cones that have summit craters, and numerous small blister-shaped domes and several irregular positive-relief, likely extrusive features (Fig. 1). An ideal landing site would provide access to one of the large cones such as Alpha, and one of the small domes, e.g., just southeast of Beta in Fig. 1; materials mass-wasted from the positive-relief volcanic features can be sampled at their base near the topographic level of the proposed landing site. Pyroclastic materials mixed into the regolith should be accessible in most locations. Chemical analysis, e.g., by gamma-ray, x-ray, and neutron spectrometers, can address key questions of lithology, volatile contents, and origin. Reflectance spectroscopy can be used to provide geologic context and reveal mineralogic variations and siting of any OH enrichment. The CBVC was a Constellation Region of Interest  and there presently exists sufficient data to certify a safe landing site for future mission. Acknowledgements: NASA for support of LRO, and LRO science & operations teams for collection and production of data used to support landing site analysis. References:  Glotch et al. (2010) Science 329, 1510-1513;  Greenhagen et al. (2010) Science 329, 1507-1509;  Jolliff et al. (2011) Nat. Geosci. 4, 566-571;  Glotch et al. (20178) this Workshop;  Zanetti (2015) Ph.D. Dissertation, Washington University;  Chauhan et al. (2015) Icarus 253, 115-129;  Watkins et al. (2017) Icarus 285, 169-184;  Lawrence et al. (2000) J. Geophys. Res. 105, 20307-20331;  Petro et al. (2013) Lunar Planet. Sci. 44, #2688;  Bhattacharya et al. (2013) Current Science 105, 685-691;  Wilson et al. (2015) J. Geophys. Res. 120;  Shirley et al. (2016) Icarus 273, 214-223.  Gruener and Joosten (2009) NASA Constellation Program Office regions of interest on the Moon: A representative basis for scientific exploration, resource potential, and mission operations, Lunar Reconnaissance Orbiter Science Targeting Meeting, Tempe, Arizona, p. #6036.