Lunar Non-Mare Volcanism: The Role Of Commercial Missions In The Exploration Of The Gruithuisen Domes

Author: 
James Head
Abstract Title: 
Lunar Non-Mare Volcanism: The Role Of Commercial Missions In The Exploration Of The Gruithuisen Domes
Abstract Type: 
Oral
Abstract Body: 
Introduction: The Gruithuisen domes are locat-ed at the outer rim of the Imbrium basin [1] in the NW portion of the Procellarum KREEP Terrane (PKT) [2] enhanced concentrations of Th [3]. The domes represent distinctive spectral features on the Moon, the red spots [4 11]. The three, steep-sided mountains (NW, Gamma, and Delta) that are dis-tinctly different from mare-type domes [12,13]; the overall shape suggests that they formed by erup-tions of high-viscosity, SiO2-rich magmas [14], resembling the smaller features that characterize the Compton-Belkovich region [15], a distinctive Th anomaly outside PKT [15]. Association with the Th-anomaly was interpreted as evidence for compositionally evolved lunar volcanism [15]. In contrast, the Gruithuisen domes are much more prominent structures [1]. CSFD on the summit plateaus of the G-γ and G-δ domes [21] indicate a similar age, ~3.8 Ga (G-γ) and 3.77 Ga (G-δ), con-sistent with those reported earlier [16,17]. Here we present a strategy for involvement of commercial spacecraft in the exploration of these types of fea-tures, focusing on the Gruithuisen domes designed to provide constraints on models of formation of non-basaltic volcanic features on the Moon. Dimensions: The Gruithuisen-NW dome is a rounded (~6.4x8 km) cone-like structure with steep (~15-20o, Fig. 1a) slopes. A break in slope at -1800 m contour marks the base of the dome and the top of the dome is at ~-600 km; its total height is ~1.2 km and the total exposed volume ~30 km3. The Gruithuisen-gamma (G-γ) dome is a flat-topped, slightly elongated mountain (~19x24.5 km), which is ~1.2 m high. Its exposed volume is ~130 km3. The base of the dome within the high-lands occurs at an elevation of ~-1900 m (Fig. 1b). The dome has a flat summit plateau (10x15 km) that is tilted northward and outlined by a promi-nent break in slope at ~-700 m. The pattern of the DTM contour lines indicates that flanks of the dome are mostly a series of facets with flat or slightly concave inward surfaces. The N and NE flanks of the dome are steeper, ~18-20o, than the S and SW flanks, ~11o (Fig.1a). Topographic pro-files show that the SW flank of the dome is slightly concave downward and a low (~100 m) scarp out-lines its base. Gruithuisen-delta (G-δ) is elongated in a NW di-rection (~35x18 km); it has a flat summit area con-sisting of a higher part (-300 m, NW side) and a lower part (-700 m, SE side). The maximum height of the dome is ~1.7 km and its total exposed vol-ume is estimated to be ~700 km3. The SW flank consists of a series of facets; facet slopes can be as steep as 15-20o (Fig. 1a). The NW and NE sides appear as broad lobes with lower, 7-9o, slopes. Strategy: We have outlined a series of Lander-Rover-Sample Return (L-R-SR) missions designed to land on the flat summits of the Gruithuisen-gamma (G-γ) and Gruithuisen-delta (G-δ) domes, document the surface morphological, mineralogi-cal, elemental and petrological characteristics lead-ing up to sample return, in order to resolve the im-portant questions about their petrogenesis and the thermal evolution of the Moon (19-20). References: 1) Head et al. LPSC-9, 488, 1978; 2) Jollif et al., JGR, 105, 4197, 2000; 3) Petro, NG, 4, 499, 2011; 4) Whitaker, The Moon, 4, 348, 1972; 5) Malin, EPSL, 21, 331, 1974; 6) Head, McCord, Science, 199, 1433, 1978; 7) Chevrel, S.D. et al. LPSC-25, 249, 1994; 8) Chevrel et al. LPSC-26, 241, 1995; 9) Chevrel et al. LPSC-27, 215, 1996; 10) Chevrel et al. JGR, 104, p. 16515, 1999; 11) Kusuma. et al. PSS 67, 46, 2012; 12) Head, Gifford, Moon, 22, 235, 1980; 13) Braden, et al. LPSC-41, #2677, 2010; 14) Wilson, J. Head, JGR, 108, 10.1029/2002JE001909, 2003; 15) Jolliff et al., NG, 4, 566, 2011; 16) Wagner et al. LPSC, #1619, 2002; 17) Wagner et al. JGR, 107, 10.1029/2002JE001844, 2002; 18) Neukum et al. SSR, 96, 55, 2001; 19. Wilson, Head, Icarus 283, 146, 2017; 20) Head, Wilson, Icarus, 283, 176, 2017. 21) Ivanov et al., Icarus 273, 262, 2016.
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Co-Authors: 
M. A. Ivanov (1,2), J. W. Head (2), and Lionel Wilson (3). (1) Vernadsky Inst., RAS, Moscow, Russia, (2) Dept. Earth, Env. and Planetary Sci, Brown Univ., Providence RI, 02912 USA, (3) Lancaster Env. Centre, Lancaster Univ., Lancaster LA1 4YQ, UK.