41st Lunar and Planetary Science Conference (2010) 1583.pdf LROC AND OTHER REMOTE SENSING STUDIES OF PYROCLASTIC DEPOSITS IN THE MARE HUMORUM REGION. B.R. Hawke 1, T.A. Giguere 1,2 , S.J. Lawrence 3, B.A. Campbell 4, L.R. Gaddis 5, J. O. Gustafson 6, J.J. Hagerty 5, C.A. Peterson 1, M.S. Robinson 3 and the LROC Team, 1Hawaii Institute of Geophysics and Planetology, Univ. of Hawaii, Honolulu, HI 96822, 2Intergraph Corporation, P.O. Box 75330, Kapolei, HI 96707, 3School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85281, 4Center for Earth and Planetary Studies, National Air and Space Museum, Washing- ton, D.C. 20560, 5U.S. Geological Survey, Astrogeology Science Center, 2255 N. Gemini Drive, Flags- taff, AZ 86001, 6Dept. of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY 14853. Introduction: In recent years, interest in image cube served as the basis for the produc- lunar dark mantle deposits of pyroclastic origin tion of a number of data products, including opt- has greatly increased. This interest is due partly ical maturity (OMAT) images and FeO and TiO 2 to the results of intensive studies of lunar pyroc- maps [8, 9]. In addition, Earth-based telescopic lastic glasses [e.g., 1, 2], as well as remote sens- near-IR reflectance spectra obtained for various ing investigations of both localized and regional units in the Humorum region were utilized in pyroclastic deposits [3, 4]. Laboratory analyses this investigation. The depolarized 12.6-cm and of pyroclastic spheres from several regional de- 70-cm radar images recently obtained by Camp- posits show that this volcanic debris had a bell et al . [10, 11] were used to assess the sur- greater depth of origin and lesser fractional crys- face textures and block populations of pyroclas- tallization than mare basalts [e.g., 1, 5]. These tic units in the Humorum region. Finally, high- data indicate that pyroclastic glasses are the best resolution LROC NAC images were used to in- examples of primitive materials on the Moon, vestigate surface characteristics and block popu- and they are of critical importance both in cha- lation [12, 13]. NAC frames M111885077 R&L racterizing the lunar interior and as a starting have resolutions of 0.50 m/pixel and place for understanding the origin and evolution M104806442R&L have resolutions of 0.77 of lunar basaltic magmatism [4]. Interest in re- m/pixel. gional dark mantle deposits has also been in- Results and Discussion: creased by the suggestion that pyroclastic debris Deposit Location, Characteristics, and Ge- would be an excellent lunar resource, and that ology. A very large pyroclastic deposit of re- pyroclastic deposits would be prime sites for the gional extent has been identified in the south- establishment of lunar bases [6]. Additional western portion of Mare Humorum [14, 15]. remote sensing and geologic studies are needed The elongate deposit extends from Liebig F in to assess the full resource potential of regional the NW to Doppelmayer G in the SE and has an pyroclastic deposits and address key scientific area of ~1475 km 2 [4]. The SW Humorum issues concerning their origin. We have used (SWH) pyroclastics largely overlie older mare LROC images and a wide variety of remote basalt deposits. The eastern portion of the SWH sensing data to investigate pyroclastic deposits unit is embayed by younger mare basalts. The in the Mare Humorum region. The goals of this 12.6-cm and 70-cm radar data indicate that the study are to: 1) identify and map the extent of pyroclastics are thickest (>10m) in an area that pyroclastic deposits, 2) determine the composi- extends for ~15 km on each side of Rima Dop- tion and degree of contamination of the regional pelmayer I. To the west, the SWH deposit be- deposits, 3) measure deposit thicknesses, and 4) comes much thinner. The thick portion of the assess their resource potential. SWH unit exhibits a low albedo, high FeO val- Methods: The U.S.G.S. has published on ues (16-18 wt%), and very low OMAT values. CD-ROM a Clementine 5-color UV-VIS digital The thinner SWH deposits have slightly higher image model for the Moon [e.g., 7]. Data from albedo values and lower FeO abundances. The this model were mosaicked to produce an image depolarized 12.6-cm and 70-cm radar images cube for the Humorum region. This calibrated were used to characterize centimeter- to decime- 41st Lunar and Planetary Science Conference (2010) 1583.pdf ter-scale rock abundances over a range of depths rum and Doppelmayer regional pyroclastic de- within the thickest portion of the SWH deposit. posits. We note that compositions of all por- The low returns in both of these data sets indi- tions of both of the very large pyroclastic depo- cate a rock-poor area that would be well-suited sits of regional extent in the Mare Humorum for resource exploitation. region are dominated by Fe 2+ -bearing pyroclas- A second very large regional pyroclastic de- tic glasses. posit has been identified in and SE of Doppel- LROC Images of the SWH pyroclastics. A mayer crater [14, 15]. The thickest portions of mosaic of 4 NAC frames was used to investigate this deposit are located on the NE floor and rim the geology and surface characteristics of a por- of Doppelmayer. Dark mantling materials were tion of the thickest part of the SWH deposit. In also identified on the NW and SE flanks of the general, the area is dark, flat, and smooth. Steep crater. The Doppelmayer pyroclastic deposit slopes are only associated with Rima Doppel- extends to the SE and occurs in and around Vi- mayer I, small crater interiors, and a mare ridge. tello crater. The thickest portions of the Dop- The sizes and locations of blocks >1 m were pelmayer deposit exhibit low albedo values, measured and recorded, and a block distribution high FeO abundances (16-18 wt%), and low map was prepared for the study area. The high- OMAT values. The depolarized 70-cm radar est block density is exhibited by the walls of returns from these thick pyroclastic deposits are Rima Doppelmayer I. Blocks as large as 22 m attenuated but are not as low as those measured were measured, and 10 m blocks are not un- for the SWH unit. The relatively high depola- common inside the rille. High block densities rized 70-cm returns from the dark material on are also associated with portions of the mare the flanks of Vitello indicate that the pyroclastic ridge in the northern portion of the study area deposit is thin (<7 m) in this area. and some of the larger impact craters in the area. Other dark mantle deposits of pyroclastic The flat surface of the SWH pyroclastic deposit origin have been identified in the Mare Humo- is largely free of blocks larger than 1 m. These rum region. These include the small, localized block distribution studies fully confirm the 70- pyroclastic deposits on the floor of Mersenius cm radar results that implied that the pyroclastic [4, 16], the dark mantle deposit NE of Liebig surface was deficient in blocks >1 m across. [14], the pyroclastic unit NE of Loewy, and a Finally, we used the available LROC NAC small dark mantle deposit on Rupes Kelvin. frames to search for the source vents of the Deposit Composition. To determine the SWH pyroclastic deposit. No vent-like struc- compositions of the regional pyroclastic units in tures were identified. We will continue to use the Mare Humorum region, five Earth-based NAC images as they are obtained to search for near-IR reflectance spectra were obtained for source vents along Rima Doppelmayer I. these deposits using the University of Hawaii References: [1] Shearer C. and Papike J. (1993) 2.24-m telescope at the Mauna Kea Observato- GCA, 57, 4785. [2] Hagerty J. et al. (2006) GCA, 70, ry. Spectra were collected for three portions of 3457. [3] Gaddis L. et al. (1985) Icarus, 61, 461. [4] the SW Humorum deposit and two spots on the Gaddis L. et al. (2003) Icarus, 161, 262. [5] Papike J. et al. (1998) Revi. Miner., 36, 5.1. [6] Hawke B. et al. Doppelmayer deposit. The spectra of these five (1990) PLPSC 20, 249. [7] Eliason E. et al. (1999) areas share similar spectral characteristics. LPSC XXX, #1933. [8] Lucey P. et al. (2000) JGR, They all exhibit steep infrared continua, low 105(E8), 20,297. [9] Lucey P. et al. (2000) JGR, albedoes, and very broad absorption bands (>0.4 105(E8), 20,377. [10] Campbell B. et al. (2007) IEEE µm) centered longward of 1 µm. Similar para- Trans. Geosci. Rem. Sensing, 45, 4032. [11] Campbell meters were determined for the spectra collected B. et al. (2008) Geology, 36, 135. [12] Robinson M. et al. (2005) LPS XXXVI, Abstract #1576. [13] Robinson for the pyroclastic deposits on the Aristarchus M. et al. (2006) 36th COSPAR, Abstract #1104. [14] Plateau [3, 17, 18]. Numerous workers have Titley S. (1967) U.S.G.S. Map I-495 . [15] Pieters C. et 2+ attributed these characteristics to Fe -bearing al. (1975) PLSC 6, 2689. [16] Hawke B. et al. (1993) pyroclastic glass [3, 4, 17, 18]. We also GRL, 20, 419. [17] Hawke B. et al. (1983) LPSC XIV, attribute these spectral characteristics to the 289. [18] Lucey P. et al. (1986) PLPSC 17, D344. presence of Fe 2+ -bearing glass in the SW Humo-.