Geologic Mapping of the Planck Quadrangle of the Moon (Lq-29)

47th Lunar and Planetary Science Conference (2016) 1188.pdf

GEOLOGIC MAPPING OF THE PLANCK QUADRANGLE OF THE MOON (LQ-29). R.A. Yingst1, F.C. Chuang1, D.C. Berman1, and S.C. Mest1; 1Planetary Science Institute (1700 E. Fort Lowell, Suite 106, Tucson, AZ 85719; [email protected]).

Introduction: A new systematic lunar geologic 1000 nm) and near-infrared (6 bands between 1100- mapping effort has endeavored to build on the success 2780 nm) data. We examined the 750/950 nm, 750/415 of earlier mapping programs by fully integrating the nm, and 415/750 nm band ratios. The 750/950 nm ratio many disparate new datasets using Geographic Infor- indicates FeO content; the deeper the absorption fea- mation Systems (GIS) software and bringing to bear ture, the greater the FeO content. The other band ratios the most current understanding of lunar geologic histo- measure the “continuum slope;" the younger the soil, ry [1, 2]. This new mapping effort began with the divi- the flatter the slope. LOLA data yields topographic sion of the Moon into 30 quadrangles and preliminary information at 100 m/pixel. LRO Narrow Angle Cam- mapping of the Copernicus Quadrangle [3, 4]. As part era (NAC) images provide non-global, high resolution of this effort, we present a 1:2,500,000-scale map of (0.5 m/pixel at 50 km altitude) panchromatic images of the Planck Quadrangle (LQ-29; Figure 1). Using tradi- the lunar surface. NAC images were used when identi- tional and current (digital) photogeologic mapping fication of small features and textures on scales of tens techniques, we identified and mapped 19 geologic of meters was required to confirm unit characteristics units and 14 linear feature types, which collectively and to refine contact locations. document major episodes of unit emplacement and Geologic units: Morphology and topography to- modification. Superposition, cross-cutting relations, gether provided sufficient information to define most and analysis of impact crater size-frequency distribu- units and determine most unit boundaries. Units tions yielded relative and modeled absolute ages of grouped by geographic setting include terra, plains, map units, as well as chronostratigraphic ages for all and basins, with some containing multiple units subdi- impact craters > 2 km in diameter. vided by age and primary morphologic character. Terra Physiographic setting: Planck Quadrangle extends units include ancient highlands (pNth), rugged terra from -30° to -60° latitude and 120° to 180° longitude; representing the SPA floor (pNtr), and knobby terra to the south, it borders the South Pole Quadrangle around Ingenii basin (pNtk). Smooth plains (pNps) are (LQ-30) [5]. The area included in Planck Quadrangle iron-enriched plains materials with a morphology that was mapped previously at 1:5,000,000 scale by [6-8]. might be indicative of impact melt. Basin units (Nbr, The western portion of the pre-Nectarian South Pole- pNbf, pNbr1, pNbr2) include those associated with the Aitken (SPA) impact feature covers much of the quad- impact structures Poincaré, Planck, Ingenii, Leibnitz rangle’s area. SPA has multiple, overlapping impact and Von Kármán. structures superposed on its floor, from sizes below Lithologic units include volcanic and impact cate- resolution to over 600 km across, with ages ranging gories. Volcanic products are primarily discrete, non- from pre-Nectarian to Copernican. Several of these contiguous mare deposits occurring exclusively within, structures contain effusive volcanic mare deposits. or breaching the rims of, craters or basins (smooth Data and Mapping Methods: The ~ 100 m/pixel mare material; Ims). The composition is primarily ba- Lunar Reconnaissance Orbiter Camera (LROC) Wide saltic, similar to the nearside maria, but low in Fe and Angle Camera (WAC) global mosaic formed the Ti. Other volcanic features include domes, wrinkle basemap for our mapping. This dataset provides a 3x ridges, sinuous rilles and dark, Fe-rich plains (pNpd). improvement in resolution over Lunar Orbiter images Patches of smooth material enriched in FeO but buried along with global nadir coverage. Additionally, we or mixed into the regolith through impact activity used LRO Lunar Orbiter Laser Altimeter (LOLA) [9, (cryptomare [12]) are mapped as mantled mare (Nmm, 10] and LRO WAC DTMs [11] to characterize the Imm). Other important basin or impact materials in- topographic expression of the surface and understand clude the high-albedo, surficial swirl-like markings of processes in vertical cross-section. The gridded LOLA the Reiner Gamma class in Mare Ingenii (s). and WAC DTMs provide complete coverage of the Geologic History: The geologic record in the pre- lunar surface at a resolution of ~100 m/pixel, and rep- Nectarian period was dominated here by large impacts, resent the most refined spatial and vertical (~1 including those that formed the Poincaré (~4.07 Ga), m/pixel) resolutions acquired for the Moon. Planck (~4.06 Ga), Jules Verne (~4.01 Ga) and Von Morphological features were mapped using the Kármán (~3.97 Ga) basins. The oldest terra units are basemap, while Clementine multispectral data were the rugged and highlands terra (~4.06 Ga). The smooth utilized to extract compositional information. Cover- plains unit (pNps) and iron-rich dark plains unit age includes ultraviolet/visible (5 bands between 415- (pNpd) are also dated as pre-Nectarian, essentially 47th Lunar and Planetary Science Conference (2016) 1188.pdf

contemporaneous with each other at ~4.00 and ~3.98 +/- 0.02 Ga). This age is not consistent with an origin Ga respectively. by young cometary impact or meteoroid scour. Rather, Key events that occurred during the Nectarian in- it is more likely associated with processes involved clude the formation of the Ingenii (~3.91 Ga) and with shielding or sorting of particles by a magnetic Leibnitz (~3.88 Ga) basins, and the emplacement of field associated with the Imbrium antipode [14]. mare within a crater at -51°N, 128°E inside Planck. References: [1] Gaddis, L. (2002), Abs. Annual Crater statistics for all these areas are within, or nearly Mtg. Planetary Mappers, USGS Open-File Report 02- within, each other’s error bars, suggesting that these 412. [2] Gaddis, L. et al. (2004) Abs. Annual Mtg. events happened within at most a few tens of millions Planetary Mappers, USGS Open-File report 2004- of years of each other. Ingenii ejecta would likely have 1289. [3] Gaddis, L. et al. (2006) Lunar Planet Sci. covered most of the quadrangle, mantling any older Conf., 37th, Abs. #2135. [4] Skinner, J. et al. (2006) mare deposits, if they existed [13]. Abs. Annual Mtg. Planetary Mappers, USGS Open- Most volcanic deposits are late Imbrian. The larger File Report 2006-1263. [5] Mest, S.C., and L.E. Van ponds all cluster within ~3.74-3.71, except for one Arsdall (2008) NASA Lunar Science Institute Lunar pond in Pauli crater (~3.61 Ga), and one NE of Poinca- Conference, 2089. [6] Stuart-Alexander, D. (1978) ré in a highly degraded crater (~3.79 Ga). One possible U.S. Geol. Surv. Map, I-1047. [7] Wilhelms, D. and F. interpretation based on the < 20 My of chronological El-Baz (1977) U.S. Geol. Surv. Map, I-948. [8] Wil- separation of most mare ponds, is to consider all mare helms et al. (1979) U.S. Geol. Surv. Map, I-1162. [9] deposits as contemporaneous. However, the ponds in Smith, D. et al. (2010) Space Sci. Rev., 150, 209–241. and around Poincaré were previously dated lower Im- [10] Zuber, M. et al. (2010) Space Sci. Rev., 150, 63– brian by [8], and the two largest ponds in this area both 80. [11] Scholten, F. et al. (2012), J. Geophys. Res., pre-date all mare deposits except for the oldest, likely 117, E00H17. [12] Hawke, B.R. et al. (1990) LPI- less affected by Ingenii ejecta. These observations are LAPST Wksp on Mare Volcanism and Basalt Petro- consistent with an older age for the two deposits. genesis, p. 5-6. [13] Whitten, J. and J. Head (2015) The knobby terra unit (pNtk) is dated at the begin- Icarus, 247, 150-171. [14] Hood, L., A. Zakharian, J. ning of the early Imbrian (~3.83 Ga), consistent with Halekas, D. Mitchell, R. Lin, M. Acuña, and A. Binder the interpretation that it is associated with terrain dis- (2001) J. Geophys. Res., 106, 27,825-27,839. ruption at the antipode of the Imbrium basin. The surficial swirls (s) are also dated as early Imbrian (~3.78

Figure 1. Geologic map of the Planck Quadrangle (LQ-29) of the Moon.