Mare Smythii Research Articles

Compositional diversity in the Mare Marginis and Mare Smythii: An insight into the volcanism in the region

The Marginis-Smythii region of the eastern limb of the Moon is a unique geological setting with the presence of equally widespread volcanism both inside and outside of an impact basin. Mare Marginis (13.3°N, 86.1°E) is a large mare deposit lying north of the pre-Nectarian Smythii Basin (13.3°N, 86.1°E). The basalts from Mare Marginis are deposited in a topographically low area outside an impact basin, i.e. the Smythii Basin. The Marginis-Smythii region is important to understand the geological controls on basalt emplacement on the Moon. In this study, we carry out a detailed investigation of the Mare Marginis and Mare Smythii basalts using the Moon Mineralogy Mapper (M3) data to understand the compositional diversity of the basalt deposits. Our study reveals that the basalts in the Mare Marginis can be divided into two distinct units: i) the central and eastern Marginis basalts that are spectrally similar to the Mare Smythii basalts, and ii) the western lacus, described as Margins west which is a small basalt deposit in the western fringes of Mare Marginis having a spectral composition different from the rest of Mare Marginis and Mare Smythii. We report that the volcanism in this compositionally distinct unit of Marginis west occurred up to ∼3.1 Ga when volcanism was still active in the Smythii Basin. We found that the volcanism in Mare Marginis was influenced by both; Crisium and Smythii Basins implying that the pre-existing structures in the lunar crust generated by large-scale impacts play an important role in the volcanism on the Moon.

Special Thermophysical Features of Floor Materials in Mare Smythii Indicated by CE-2 CELMS Data

Mare Smythii is a special basin, which is one of the oldest mare basins with the considerably young mare basalts and the high density of floor-fractured craters. In this article, the microwave sounder, named CELMS, onboard Chang'E-2 lunar orbiter was first invested to assess the thermophysical characteristics of the floor materials in mare Smythii. Based on the numerical simulation with the radiative transfer model and the previous geological results, several special findings are noted as follows. First, the substrate temperature in mare Smythii is likely fairly high, and a special temperature structure is provided. Second, there likely exists an unrevealed deposit in the upper layer of the regolith with strong thermal absorption ability. Third, the CELMS results show a strong correlation with the subsurface features obtained by lunar radar sounder data and the surface wrinkle ridges. These findings will be of essential importance to strengthen knowing the thermal and magmatic evolutions of the lunar maria.

3D inversion of full gravity gradient tensor data in spherical coordinate system using local north-oriented frame

In this paper, we propose an inverse method for full gravity gradient tensor data in the spherical coordinate system. As opposed to the traditional gravity inversion in the Cartesian coordinate system, our proposed method takes the curvature of the Earth, the Moon, or other planets into account, using tesseroid bodies to produce gravity gradient effects in forward modeling. We used both synthetic and observed datasets to test the stability and validity of the proposed method. Our results using synthetic gravity data show that our new method predicts the depth of the density anomalous body efficiently and accurately. Using observed gravity data for the Mare Smythii area on the moon, the density distribution of the crust in this area reveals its geological structure. These results validate the proposed method and potential application for large area data inversion of planetary geological structures.

Multiple lithic clasts in lunar breccia Northwest Africa 7948 and implication for the lithologic components of lunar crust

AbstractThis study presents the petrography, mineralogy, and bulk composition of lunar regolith breccia meteorite Northwest Africa (NWA) 7948. We identify a range of lunar lithologies including basaltic clasts (very low‐titanium and low‐titanium basalts), feldspathic lithologies (ferroan anorthosite, magnesian‐suite rock, and alkali suite), granulites, impact melt breccias (including crystalline impact melt breccias, clast‐bearing impact melt breccias, and glassy melt breccias), as well as regolith components (volcanic glass and impact glass). A compositionally unusual metal‐rich clast was also identified, which may represent an impact melt lithology sourced from a unique Mg‐suite parent rock. NWA 7948 has a mingled bulk rock composition (Al2O3 = 21.6 wt% and FeO = 9.4 wt%) and relatively low concentrations of incompatible trace elements (e.g., Th = 1.07 ppm and Sm = 2.99 ppm) compared with Apollo regolith breccias. Comparing the bulk composition of the meteorite with remotely sensed geochemical data sets suggests that the sample was derived from a region of the lunar surface distal from the nearside Th‐rich Procellarum KREEP Terrane. Our investigations suggest that it may have been ejected from a nearside highlands‐mare boundary (e.g., around Mare Crisium or Orientale) or a cryptomare region (e.g., Schickard‐Schiller or Mare smythii) or a farside highlands‐mare boundary (e.g., Mare Australe, Apollo basin in the South Pole–Aitken basin). The distinctive mineralogical and geochemical features of NWA 7948 suggest that the meteorite may represent lunar material that has not been reported before, and indicate that the lunar highlands exhibit wide geological diversity.

Difference of brightness temperatures between 19.35 GHz and 37.0 GHz in CHANG’E-1 MRM: implications for the burial of shallow bedrock at lunar low latitude

Indications of buried lunar bedrock may help us to understand the tectonic evolution of the Moon and provide some clues for formation of lunar regolith. So far, the information on distribution and burial depth of lunar bedrock is far from sufficient. Due to good penetration ability, microwave radiation can be a potential tool to ameliorate this problem. Here, a novel method to estimate the burial depth of lunar bedrock is presented using microwave data from Chang’E-1 (CE-1) lunar satellite. The method is based on the spatial variation of differences in brightness temperatures between 19.35 GHz and 37.0 GHz (ΔTB). Large differences are found in some regions, such as the southwest edge of Oceanus Procellarum, the area between Mare Tranquillitatis and Mare Nectaris, and the highland east of Mare Smythii. Interestingly, a large change of elevation is found in the corresponding region, which might imply a shallow burial depth of lunar bedrock. To verify this deduction, a theoretical model is derived to calculate the ΔTB. Results show that ΔTB varies from 12.7 K to 15 K when the burial depth of bedrock changes from 1 m to 0.5 m in the equatorial region. Based on the available data at low lunar latitude (30°N-30°S), it is thus inferred that the southwest edge of Oceanus Procellarum, the area between Mare Tranquillitatis and Mare Nectaris, the highland located east of Mare Smythii, the edge of Pasteur and Chaplygin are the areas with shallow bedrock, the burial depth is estimated between 0.5 m and 1 m.

Mare volcanism: Reinterpretation based on Kaguya Lunar Radar Sounder data

The Lunar Radar Sounder (LRS) onboard Kaguya (SELENE) detected widespread horizontal reflectors under some nearside maria. Previous studies estimated that the depths of the subsurface reflectors were up to several hundreds of meters and suggested that the reflectors were interfaces between mare basalt units. The comparison between the reflectors detected in the LRS data and surface age maps indicating the formation age of each basalt unit allows us to discuss the lower limit volume of each basalt unit and its space and time variation. We estimated volumes of basalt units in the ages of 2.7 Ga to 3.8 Ga in the nearside maria including Mare Crisium, Mare Humorum, Mare Imbrium, Mare Nectaris, Mare Serenitatis, Mare Smythii, and Oceanus Procellarum. The lower limit volumes of the geologic units estimated in this study were on the order of 103 to 104 km3. This volume range is consistent with the total amount of erupted lava flows derived from numerical simulations of thermal erosion models of lunar sinuous rille formation and is also comparable to the average flow volumes of continental flood basalt units formed after the Paleozoic and calculated flow volumes of Archean komatiite flows on the Earth. The lower limits of average eruption rates estimated from the unit volumes were on the order of 10−5 to 10−3 km3/yr. The estimated volumes of the geologic mare units and average eruption rate showed clear positive correlations with their ages within the same mare basin, while they vary among different maria compared within the same age range.

Refinement of lunar TiO2 analysis with multispectral features of Chang’E-1 IIM data

We develop a method based on the samples from Apollo and Luna landing sites to determine lunar TiO2 content with Chang’E-1 interference imaging spectrometer (IIM) imagery. By analyzing the nonlinear relationship between the optical and compositional parameters of lunar soil samples, the method employs two Support Vector Machines (SVMs) to estimate the titanium abundance of the lunar surface. Developed with the soil compositions of the Apollo and Luna sample-return stations, the RMS (root mean square) error of our method is 0.24 wt% TiO2, and the correlation coefficient of the TiO2 values and our predicted ones is 99.72 %. Compared with the other 3 models, the method proposed in this paper exhibits a good performance for determining the chemical composition of the lunar surface. TiO2 maps of Sinus Iridum, part of the Marius Hills plateau, and part of Mare Smythii are produced using our method, which could be useful for future lunar missions.

Ages and stratigraphy of lunar mare basalts in Mare Frigoris and other nearside maria based on crater size‐frequency distribution measurements

We report on ages derived from impact crater counts for exposed mare basalt units in the northern part of the lunar nearside hemisphere (Mare Frigoris), the eastern and northeastern part of the nearside hemisphere (Lacus Temporis, Joliot, Hubble, Goddard, Mare Marginis, and Mare Smythii), the central part of the nearside hemisphere (Palus Putredinis, Mare Vaporum, and Sinus Medii), and the southwestern part of the nearside hemisphere (Grimaldi, Crüger, Rocca A, Lacus Aestatis, and Schickard). In Mare Frigoris, we dated 37 basalt units, showing ages from 2.61 to 3.77 Gyr, with most units being formed in the late Imbrian period between 3.4 and 3.8 Gyr ago. In Mare Vaporum we dated six spectrally homogeneous units that show model ages of 3.10 to 3.61 Gyr. Our model ages of basalts in Mare Marginis range from 3.38 to 3.88 Gyr and are mostly older than basalts in Mare Smythii (3.14–3.48 Gyr). The model ages of four units in Sinus Medii indicate that the basalts in this region formed 3.63 to 3.79 Gyr ago. We find an excellent agreement of our crater size‐frequency model ages of the Palus Putredinis area, which contains the Apollo 15 landing site, with the radiometric ages of Apollo 15 samples. According to our crater counts, basalts in Palus Putredinis are 3.34 Gyr old and this compares favorably with the radiometric ages of 3.30–3.35 Gyr of the olivine‐normative and quartz‐normative basalts of the Apollo 15 landing site. Lacus Aestatis is a small irregular‐shaped mare patch in the southwestern nearside and shows an Imbrian age of 3.50 Gyr; basalts in Lacus Temporis in the northeastern nearside formed between 3.62 and 3.74 Gyr ago and are, therefore, older than the basalts in Lacus Aestatis. We found that basalts in craters of the southwestern nearside (Schickard, Grimaldi, Crüger, and Rocca A) are also mostly younger than basalts in craters of the northeastern nearside (Hubble, Joliot, and Goddard). While basalt ages vary between 3.16 and 3.75 Gyr in the southwest, basalts in the northeast are 3.60–3.79 Gyr old. These results confirm and extend the general distribution of ages of mare basalt volcanism and further underline the predominance of older mare basalt ages in the eastern and southern nearside and in patches of mare peripheral to the larger maria, in contrast to the younger basalt ages on the western nearside (Oceanus Procellarum).

Ages and stratigraphy of mare basalts in Oceanus Procellarum, Mare Nubium, Mare Cognitum, and Mare Insularum

Accurate estimates of mare basalt ages are necessary to place constraints on the duration and the flux of lunar volcanism as well as on the petrogenesis of lunar mare basalts and their relationship to the thermal evolution of the Moon. We performed new crater size‐frequency distribution measurements in order to investigate the stratigraphy of mare basalts in Oceanus Procellarum and related regions such as Mare Nubium, Mare Cognitum, and Mare Insularum. We used high‐resolution Clementine color data to define 86 spectrally homogeneous units within these basins, which were then dated with crater counts on Lunar Orbiter IV images. Our crater size‐frequency distribution measurements define mineralogical and spectral surface units and offer significant improvements in accuracy over previous analyses. Our data show that volcanism in the investigated region was active over a long period of time from ∼3.93 to 1.2 b.y., a total of ∼2.7 b.y. Volumetrically, most of the basalts erupted in the Late Imbrian Period between ∼3.3 and 3.7 b.y., and we see evidence that numerous units have been resurfaced. During the Eratosthenian Period, significantly less basalt was erupted. Depending on the absolute model ages that one can assign to the lunar chronostratigraphic systems, five units might be of Copernican age. Younger basalts are generally exposed in the center of the investigated area, that is, closer to the volcanic centers of the Aristarchus Plateau and Marius Hills. Older basalts occur preferentially along the northwestern margin of Oceanus Procellarum and in the southeastern regions of the studied area, i.e., in Mare Cognitum and Mare Nubium. Combining the new data with our previously measured ages for basalts in Mare Imbrium, Serenitatis, Tranquillitatis, Humorum, Australe, and Humboldtianum, we find that the period of active volcanism on the Moon lasted ∼2.8 b.y., from ∼4 b.y. to ∼1.2 b.y. On the basis of the basalts dated so far, which do not yet include the potentially young basalts of Mare Smythii e.g.,all investigated basins but probably also is the location of some of the youngest basalts on the lunar surface.

Geology of the Smythii and Marginis region of the Moon: Using integrated remotely sensed data

We characterized the diverse and complex geology of the eastern limb region of the Moon using a trio of remote‐sensing data sets: Clementine, Lunar Prospector, and Apollo. On the basis of Clementine‐derived iron and titanium maps we classify the highlands into low‐iron (3–6 wt% FeO) and high‐iron (6–9 wt% FeO) units. The association of the latter with basalt deposits west of Smythii basin suggests that the highland chemical variation is the result of mixing between basalt and highland lithologies. Mare Smythii and Mare Marginis soils are compositionally similar, containing moderate iron (15–18 wt% FeO) and titanium (2.5–3.5 wt% TiO2). Smythii basin, in addition to the basalt deposits, contains an older, moderate‐albedo plains unit. Our investigation reveals that the dark basin plains unit has a distinct albedo, chemistry, and surface texture and formed as a result of impact‐mixing between highland and mare lithologies in approximately equal proportions. Clementine iron and maturity maps show that swirls along the northern margin of Mare Marginis have the same iron composition as the surrounding nonswirl material and indicate that the swirl material is bright because of its low agglutinate content. Gravity data for the eastern limb show high, positive Bouguer gravity anomalies for areas of thin basalt cover (e.g., Smythii basin and complex craters Joliot, Lomonosov, and Neper). We deduce that the uplift of dense mantle material is the primary (and mare basaltic fill the secondary) source for generating the concentration of mass beneath large craters and basins.

Laydown of a tether from Earth visible location to far side for lunar SETI

In order to keep about a third of the Moon far side free from radio frequency interference (RFI) of all kinds (including RFI produced by artificial satellites orbiting the Moon) this paper proposes a dedicated space mission to the far side of the Moon (SETIMOON). This is intended to set up and operate a SETI antenna inside the Saha far side crater. One important feature of SETIMOON is that no astronaut work is requested. In fact, the setting up of two antennas (one on the near side Moon plain Mare Smythii and one inside Saha), is achieved by virtue of a tethered system, in either of two ways: 1- gradually deploying the tether in orbit around the Moon until the two antennas land softly and the tether itself is also the cable connecting the two antennas; or 2- letting the Earth-link antenna in Mare Smythii land first, and then shooting from there the folded radiotelescope tied up with a tether to the crater Saha. Again the tether becomes the cable connecting the two antennas.

Characteristics of lunar mare deposits in Smythii and Marginis basins: Implications for magma transport mechanisms

An analysis of 34 lunar lava flows and ponds in the eastern limb Smythii and Marginis basins was undertaken to examine and model the first stages of secondary crustal formation and assess processes involved in magma transport and eruption. In order to isolate the characteristics of single eruptive episodes, we focused on discrete mare ponds adjacent to the major maria. Mean values for areas and volumes of deposits estimated to be good candidates for single eruptive phases are large, approximately 950–1000 km2 and ∼200 km3 respectively. These eruptive volumes are commensurate with the largest known terrestrial eruptions (flood basalts). The lack of geomorphological structures indicative of shallow magma reservoirs indicates that deep, probably subcrustal source regions are prevalent. With respect to crustal thickness relationships, the magnitude and frequency of eruptive events are observed to be greatest in areas of thinnest crust. Specifically, regions of major maria (Mare Smythii, Mare Marginis) occur in areas of thinnest crust, while isolated ponds occur where the crust is relatively thicker. This is consistent with the correlation observed globally between crustal thickness and the magnitude and frequency of eruptive events. Ages of volcanic flows and pyroclastic events range from Early Imbrian to Imbrian‐Eratosthenian but are concentrated most heavily between 3.80–3.60 Ga, suggesting a period of peak volcanism beginning around 3.85 Ga and lasting approximately 200 Ma. However, the existence of dark‐halo crater clusters in non‐mare units within the region suggests the presence of cryptomaria, which would indicate an earlier onset of volcanism and a volume of mare material potentially greater than that currently exposed on the surface. Typical nearest‐neighbor distances suggest deposits derive from reservoirs <∼100 km in diameter. The observations made here are consistent with a magma transport model in which plumes rising diapirically stall at a density boundary under the lunar crust and propagate dikes to the surface through overpressurization.

Seti Space Missions

AbstractSETI from space is currently envisaged in three ways: i) by large space antennas orbiting the Earth that could be used for both VLBI and SETI (VSOP and RadioAstron missions), ii) by a radiotelescope inside the Saha far side Moon crater and an Earth-link antenna on the Mare Smythii near side plain. Such SETIMOON mission would require no astronaut work since a Tether, deployed in Moon orbit until the two antennas landed softly, would also be the cable connecting them. Alternatively, a data relay satellite orbiting the Earth-Moon Lagrangian pointL2would avoid the Earthlink antenna, iii) by a large space antenna put at the foci of the Sun gravitational lens: 1) for electromagnetic waves, the minimal focal distance is 550 Astronomical Units (AU) or 14 times beyond Pluto. One could use the huge radio magnifications of sources aligned to the Sun and spacecraft; 2) for gravitational waves and neutrinos, the focus lies between 22.45 and 29.59 AU (Uranus and Neptune orbits), with a flight time of less than 30 years. Two new space missions, of SETI interest if ET’s use neutrinos for communications, are proposed.

Floor‐fractured craters in Mare Smythii and west of Oceanus Procellarum: Implications of crater modification by viscous relaxation and igneous intrusion models

Endogenic modification in lunar floor‐fractured craters can constrain spatial variations in early lunar conditions. The nature of these constraints, however, depends on the assumed mechanism of crater modification. For viscous relaxation, the extent of crater modification depends on the surrounding crustal viscosity and thus provides loose constraints on the history of crustal heating within a region. For igneous intrusion models, the extent of crater modification reflects magmatically driven deformation and can be inverted to estimate both local magma pressure and intrusion depth. Both models indicate clear differences between regional conditions at Mare Smythii and in the highlands west of Oceanus Procellarum. The uniformly shallow crater depths in Mare Smythii probably indicate a long‐lived period of extreme crater relaxation, whereas the wide range of modified crater depths in the western highlands suggest a much shorter period of partial crater relaxation. For comparable relaxation times, the average viscosity derived for Mare Smythii is over 10 times lower than the average viscosity inferred for the western highlands. Alternatively, if modification reflects deformation over crater‐centered, laccolithlike intrusions, the derived magma pressures indicate a broad, uniform magma source beneath Mare Smythii, whereas the spatial variation of estimated magma pressures in the western highlands suggests the presence of several, smaller magma sources. The derived intrusion depths are partly a function of crater size, but range from ∼1 to 10 km in depth for both regions and may be slightly greater on average in the western highlands. While both viscous relaxation and igneous intrusions can explain the modification of individual craters, the regional variations in these derived modification conditions also allow further testing of each modification model. In particular, the correlation of the lowest viscosities or the longest relaxation times with the smallest craters in both Mare Smythii and the western highlands seems inconsistent with crater modification by the relaxation mechanism. The onset of total relaxation at progressively smaller topographic wavelengths over time might produce such a trend in Mare Smythii, but total relaxation cannot be invoked for the western highlands, where many large craters still preserve significant fractions of their initial relief. In addition, the relaxation of the smallest craters in both regions suggests the presence of exceptionally high near‐surface thermal gradients (∼150–200 K/km). Since the observed regional variations in crater modification can be easily attributed to variations in magma pressure as a function of mantle topography, we conclude that crater floor fracturing in both regions is more consistent with the igneous intrusion mechanism than with viscous relaxation during a crustal heating event.

The lunar farside: The nature of highlands east of Mare Smythii

Available lunar orbital data were studied in detail to determine the nature and origin of geochemical variation in a portion of the farside highlands east of the Smythii basin. Such data exist for the elements Al, Mg, Fe, Ti, and Th (Clark and Hawke, 1981; Davis, 1980; Metzger et al., 1977). As in our previous studies (Clarke and Hawke, 1981, 1987), averages and ranges of concentrations for these elements are calculated and correlated for photogeologically defined units associated with features such as Babcock, King, Al-Khwarezmi, Langemak, Pasteur, and Sklodowska and with the region as a whole. In addition, comparisons are made between this and other highland regions which have been investigated by other workers in a similar manner (Andre et al., 1977; Haines et al., 1978; Maxwell and Andre, 1981). The region is shown to be distinctively enriched in the anorthositic end-members of the ANT-suite. Anomalies which have been reported for this region (Hawke et al., 1985) are confirmed by this study. An area south of Pasteur shows enrichment in some mafic components, giving evidence for the presence of buried mare basalt, and lending support to the hypothesis that volcanic activity may be fairly widespread even in the farside highlands. The units just southeast of Mare Smythii appear to be geochemically related to the area partly surrounding the Smythii on the west (Clark and Hawke, 1987). Considerable geochemical heterogeneity exists in this area, as in areas of the nearside highlands (Clark and Hawke, 1981, 1982, 1987; Hawke et al., 1985).

The origin of selected lunar geochemical anomalies: Implications for early volcanism and the formation of light plains

The Apollo orbital geochemistry, photogeologic, and other remote sensing data sets were used to identify and characterize geochemical anomalies on the eastern limb and farside of the Moon and to investigate the processes responsible for their formation. The anomalies are located in the following regions: (1) Balmer basin, (2) terrain northeast of Mare Smythii, (3) near Langemak crater, (4) Pasteur crater, (5) terrain northwest of Milne basin, (6) northeast of Mendeleev basin, (7) north and northeast of Korolev basin, (8) terrain north of Taruntius crater, and (9) terrain north of Orientale basin. The anomalies are commonly associated with Imbrian- or Nectarian-aged light plains units which exhibit dark-haloed impact craters. The results of recent spectral reflectance studies of dark-haloed impact craters plus consideration of the surface chemistry of the anomalies strongly indicate that those geochemical anomalies associated with light plains deposits which display dark-haloed impact craters result from the presence of basaltic units that are either covered by varying thickness of highland debris or have a surface contaminated with significant amounts of highlands material. The burial or contamination of ancient volcanic surfaces by varying amounts of highland material appears to have been an important (though not the dominant) process in the formation of lunar light plains. Basaltic volcanism on the eastern limb and farside of the Moon was more extensive in both space and time than has been accepted.

The distribution of titanium on the lunar surface

Titanium concentrations have been derived from measurements with the lunar-orbiting gamma-ray experiment on Apollo 15 and 16 by analyzing a spectral interval in which the titanium signal is relatively enhanced. Landing site soil values provide the reference for a regression curve from which Ti concentrations in 137 regions of adequate counting statistics are calculated. Among the mare regions overflown, the southern portion of Mare Tranquillitatis contains the highest Ti concentration (4.4%), Mare Serenitatis, Mare Fecunditatis, and Mare Smythii have intermediate values corresponding to low-Ti basalts, and Mare Crisium is conspicuously low in Ti (0.9%). Regional values in the western maria range from 1.1% to 4.1%, somewhat higher in the north than in the south, with the highest values seen south and west of Aristarchus. The Aristarchus Plateau appears chemically distinct from the surrounding mare. The younger western basalts mapped by the experiment do not appear to be identical to the Apollo 11 and Apollo 17 high-Ti basalts. Low-Ti basalts predominate in the observed mare regions. Highland Ti concentrations range from undetectable to 1.5% with several exceptions; accuracy is limited by the relatively large uncertainty. Highland results suggest a north-south asymmetry which is not consistent with previously reported results for Fe and Th. Comparisons with telescopic spectral reflectance studies of the maria do not show complete agreement and suggest that effects due to Fe may not have been fully removed from the reflectance data.

Detection of Radon Emission at the Edges of Lunar Maria with the Apollo Alpha-Particle Spectrometer

The distribution of radioactive polonium-210, a decay product of radon-222, shows enhanced concentrations at the edges of lunar maria. Enhancements are seen at the edges of Mare Fecunditatis, Mare Crisium, Mare Smythii. Mare Tranquillitatis, Mare Nubium, Mare Cognitum, and Oceanus Procellarum. The observation is indicative of the transient emission of radon gas from the perimeters of lunar maria.

Oxygen and bulk element abundances in Luna 20 fines

Abundances of O, Si, Al and Mn have been determined in Luna 20 fines sample 22001,9 by instrumental neutron activation analysis. The abundances of O, Si and Al are among the highest we have observed in lunar samples and reflect a highlands origin for much of this regolith sample. The Luna 20 abundances reported here most closely resemble those we have determined in four samples of two Apollo 16 fines, rock 14310, and a clast from breccia 15459. The Luna 20 O Si ratio of 1.96 ± 0.05 is similar to that in most other lunar samples, but the Al Si ratio of 0.532 ± 0.024 is exceeded only by our data on the Apollo 16 fines. This Al Si ratio is in agreement with the value of 0.55 ± 0.06 determined by the remote X-ray fluorescence experiment for the highlands between Mare Crisium and Mare Smythii which lie near the Luna 20 site ( Adler et al., 1972).