Aristarchus Plateau Research Articles

Ancient primary crust beneath the Aristarchus plateau: Constraints from gravity and topography data

The Moon's Aristarchus Plateau, proposed to be a complex proto-shield volcano, has relatively well-localized gravity and topography in the northwestern region, where homogenous pyroclastic deposits occur on the surface. We applied a localized admittance analysis in this region to constrain its subsurface structure. A thin lithospheric flexure model that considers both surface and subsurface loads is used to predict the gravity signal. Our results indicate no obvious dense materials in the subsurface and a thin elastic lithosphere of this region. The best-fit crustal density is 2590kgm−3 with 1−σ limits of 2400 and 2690kgm−3, and the best-fit density of the load is constrained to be 2480kgm−3, ranging from 2430 to 2530kgm−3. Both the crustal and load densities are consistent with the bulk density of lunar highlands crust, suggesting a possible ancient primary crust beneath this northwestern area. Our results indicate that ancient primary crusts existed at some locations contemporarily with the emplacement of mare basalts in Oceanus Procellarum.

The compositional distribution and rock types of the Aristarchus region on the Moon

The Aristarchus region is the brightest part for the lunar nearside. It includes diverse material types, such as the largest amount of volcanic pyroclastic deposits, very young impact ejecta from the Aristarchus crater and mare basalts surrounding the Aristarchus plateau. This region also experienced complex geologic processes including volcanic, impact and tectonic activities. In this study, we combine the ChangE-1 IIM, Lunar Prospector and Clementine UVVIS datasets to investigate the elemental distribution, mineral properties and rock types in this region. The Aristarchus region has the most variable materials including volcanic pyroclastic deposits, mare basalts, highland anorthosite, KREEP and some rare evolved rock types, which makes it one of the most scientific valuable regions for the future lunar missions (e.g., the third phase of Chinese Lunar Exploration Program).

Lunar sinuous rilles: Distribution, characteristics, and implications for their origin

Lunar sinuous rilles (SRs) are enigmatic features interpreted to have formed as the result of lava erosion into the lunar surface. While specific SRs have been studied in detail over the past few decades, the most recent general survey of these features was conducted in 1969 using Lunar Orbiter IV and V photographs. The current global study updates the catalog of SRs, using higher resolution SELENE and LRO image and topography data to provide detailed observations and measurements of the rilles observed across the lunar surface. The new survey catalogs more than 200 SRs that vary in length from 2km to 566km (median length 33.2km), in width from 160m to 4.3km (median width 480m), in depth from 4.8m to 534m (median depth 49m), in slope from −1.4° to 0.5° (median slope −0.2°), and in sinuosity index from 1.02 to 2.1 (median sinuosity 1.19). Oceanus Procellarum contains 48% of the rilles mapped in this survey, and these rilles are typically associated with the known centers of volcanism within the Procellarum-KREEP Terrain, the Aristarchus Plateau and the Marius Hills. The current study also constrains the timing of the formation of lunar SRs, using the assumptions that the incised unit represents an upper age limit and the terminal or embaying unit represents a lower age limit. Results indicate that the distribution of ages of rille formation is highly correlated with the emplacement ages of mare units, where the majority of rilles are observed to have formed between 3.0Ga and 3.8Ga ago, though some of the features associated with the Aristarchus Plateau may have formed as recently as 1.0Ga to 1.5Ga ago. The documented observations can be used to better understand how SRs formed; for example, the range of slopes observed for all rilles (−1.4° to 0.5°) indicates that thermal erosion is likely dominant during the formation of the 78% of rilles that are observed to have formed in solidified mare basalt material, though mechanical erosion is likely to have been a more significant process during the formation of the 25% of observed rilles that originate in the highlands (20% of the mapped rilles crossed from the highlands into the mare), where a thicker regolith is expected to have been more easily eroded.

Compositional diversity and geologic insights of the Aristarchus crater from Moon Mineralogy Mapper data

[1] The Moon Mineralogy Mapper (M3) acquired high spatial and spectral resolution data of the Aristarchus Plateau with 140 m/pixel in 85 spectral bands from 0.43 to 3.0 μm. The data were collected as radiance and converted to reflectance using the observational constraints and a solar spectrum scaled to the Moon-Sun distance. Summary spectral parameters for the area of mafic silicate 1 and 2 μm bands were calculated from the M3 data and used to map the distribution of key units that were then analyzed in detail with the spectral data. This analysis focuses on five key compositional units in the region. (1) The central peaks are shown to be strongly enriched in feldspar and are likely from the upper plagioclase-rich crust of the Moon. (2) The impact melt is compositionally diverse with clear signatures of feldspathic crust, olivine, and glass. (3) The crater walls and ejecta show a high degree of spatial heterogeneity and evidence for massive breccia blocks. (4) Olivine, strongly concentrated on the rim, wall, and exterior of the southeastern quadrant of the crater, is commonly associated the impact melt. (5) There are at least two types of glass deposits observed: pyroclastic glass and impact glass.

Timing and characteristics of the latest mare eruption on the Moon

Unraveling the timing and duration of mare volcanism on the Moon is essential for understanding its thermal evolution. The end of mare volcanism is poorly constrained, because mare basalts are incompletely sampled. In this study, employing SELENE (Kaguya) high-resolution images, we performed new crater size-frequency measurements for 49 young mare units (<~3.0 Ga) in the Procellarum KREEP Terrane (PKT), in which the latest magma eruption of the Moon occurred. Mare volcanism in this region continued until ~ 1.5 Ga, suggesting that volcanic activity in this region ceased ~ 1.0 Ga after the magma eruption had globally ceased 2.5–3.0 Ga. Volcanic activity may have peaked 1.8–2.2 Ga ago. The youngest basalts occur around the Aristarchus plateau and the Kepler crater, which are located in the central region of the PKT. It is likely that heating in the crust due to the concentration of heat-producing elements in the PKT delayed cooling of a partial-melting zone in the underlying mantle. In contrast with previous basalt dating in this region, our results indicate a higher correlation between ages and spectral types of mare basalts; the young mare units in the PKT tend to have spectral types corresponding to high titanium contents, while low titanium basalts occur mainly in the early stage. The titanium variation in mare basalts may reflect vertical heterogeneity in TiO 2 content in the upper mantle beneath the PKT.

Thorium abundances on the Aristarchus plateau: Insights into the composition of the Aristarchus pyroclastic glass deposits

Thorium (Th) data from the Lunar Prospector gamma ray spectrometer (LP‐GRS) are used to constrain the composition of lunar pyroclastic glass deposits on top of the Aristarchus plateau. Our goal is to use forward modeling of LP‐GRS Th data to measure the Th abundances on the plateau and then to determine if the elevated Th abundances on the plateau are associated with the pyroclastic deposits or with thorium‐rich ejecta from Aristarchus crater. We use a variety of remote sensing data to show that there is a large, homogenous portion of the pyroclastics on the plateau that has seen little or no contamination from the Th‐rich ejecta of Aristarchus crater. Our results show that the uncontaminated pyroclastic glasses on Aristarchus plateau have an average Th content of 6.7 ppm and ∼7 wt % TiO2. These Th and Ti values are consistent with Th‐rich, intermediate‐Ti yellow glasses from the lunar sample suite. On the basis of this information, we use petrologic equations and interelement correlations for the Moon to estimate the composition of the source region from which the Aristarchus glasses were derived. We find that the source region for the Aristarchus glasses contained high abundances of heat‐producing elements, which most likely served as a thermal driver for the prolonged volcanic activity in this region of the Moon.

The Aristarchus Plateau on the Moon: Mineralogical and structural study from integrated Clementine UV–Vis–NIR spectral data

Combining UVVIS and NIR Clementine spectral data, we characterize the mineralogy of the different volcanic and crustal materials occurring on the Aristarchus Plateau and its close vicinity, in order to investigate their stratigraphic relationships and understand the nature of the crust in this region of the Moon. From an iterative linear mixture modeling, we provide a comprehensive description of the distribution and amount of surface mixture of the units, and document the stratigraphic relationships in the region of study. The determination of clear relationships and origin of the different units forming the structure of the Plateau is not obvious as the surface materials (to a depth less than 1 km) represent complex materials from the Imbrium impact event. In the Aristarchus region, we show that the Imbrium ejecta has a norite and anorthosite rich composition, with the presence of a clinopyroxene component in the uppermost layer (AER and NE units in the text). Alternatively, AER may form a rather thick horizon emplaced on an NE-rich unit, or AER and NE form a single thick horizon showing a gradational compositional change from AER to NE, from the south to the north of the Plateau. Due to its size, the Aristarchus crater must have penetrated through the Imbrium ejecta and exposed underlying layers formed by pre-Imbrian ejecta and/or the original crust. The regional crustal unit (AP for “Aristarchus peak” in the text), i.e., the deepest horizon exposed by the Aristarchus crater likely originates from a pluri kilometer depth, and is represented by feldspar-rich materials with clinopyroxene and olivine as mafic components. Other deep crustal units, at a stratigraphic level close to the deepest horizon AP, or intermediate between AP and the uppermost horizon AER, and locally distributed in the Aristarchus crater and its vicinity (Aristarchus A crater, and the scarp forming the southern edge of the Plateau), are represented by pyroxene-bearing anorthosite (SC unit) and olivine-rich (OL unit) composition. Although in low abundance, olivine-rich materials are found to be widespread in this region of the Moon. Volcanic pyroclastic deposits (DMD) are widely exposed on the Plateau, with high abundances and a fairly homogeneous composition. We suggest their emplacement could have possibly lasted up to the Eratosthenian, thus leading to a more important pyroclastic activity in time than previously thought, and a rather voluminous and stable reservoir for their source. Based on their UVVIS and NIR spectral characteristics, SW-type materials characterizing the mare basalts west of the Plateau are not detected as a major component across the Plateau. However, SW-type material is significantly present in the complex ejecta of the Aristarchus crater, probably due to the particular morphology of the target, straddling the edge of the Plateau which rises about 2 km above Oceanus Procellarum. The present study based on the integrated visible–near infrared Clementine dataset paves the way for high spatial resolution surveys based on recent photometric observations (e.g., AMIE/Smart-1) and/or upcoming detailed spectroscopic observations [LISM/Kaguya–Selene; M3 (Moon Mineralogy Mapper)/Chandraayan-1].

Volcanic and impact deposits of the Moon's Aristarchus Plateau: A new view from Earth-based radar images

Lunar pyroclastic deposits reflect an explosive stage of the basaltic volcanism that filled impact basins across the nearside. These fine-grained mantling layers are of interest for their association with early mare volcanic processes, and as possible sources of volatiles and other species for lunar outposts. We present Earth-based radar images, at 12.6 and 70 cm wavelengths, of the pyroclastic deposit that blankets the Aristarchus Plateau. The 70 cm data reveal the outlines of a lava-flow complex that covers a significant portion of the plateau and appears to have formed by spillover of magma from the large sinuous rille Vallis Schroteri. The pyroclastics mantling these flows are heavily contaminated with rocks 10 cm and larger in diameter. The 12.6 cm data confirm that other areas are mantled by 20 m or less of material, and that there are numerous patches of 2 cm and larger rocks associated with ejecta from Aristarchus crater. Some of the radar-detected rocky debris is within the mantling material and is not evident in visible-wavelength images. The radar data identify thick, rock-poor areas of the pyroclastic deposit best suited for resource exploitation.

Global spatial deconvolution of Lunar Prospector Th abundances

We have completed the first global spatial deconvolution analysis of planetary gamma‐ray data for lunar Th abundances as measured by the Lunar Prospector Gamma‐ray Spectrometer. We tested two different spatial deconvolution techniques – Jansson's method and the Pixon method – and determined that the Pixon method provides superior performance. The final deconvolved map results in a spatial resolution improvement of a factor of 1.5–2. The newly deconvolved data allow us to clearly delineate nearside Th enhancements and depressions, validate enhanced Th abundances associated with specific lunar red spots, and reveal new details of the Th distribution at the Aristarchus plateau.

Radiative transfer modeling of compositions of lunar pyroclastic deposits

While over 100 lunar pyroclastic deposits have been identified remotely, their compositions remain poorly constrained. In this work, we determine the compositions of three lunar regional pyroclastic deposits which are likely to contain large amounts of glass and for which we have high‐quality ground‐based spectra: the Aristarchus Plateau, Mare Humorum, and Sulpicius Gallus. We use radiative transfer theory and employ measured optical constants of glasses to predict the bidirectional reflectance of a particulate glass surface as a function of Fe and Ti concentration, particle size, and maturity in order to find the best spectral match to the remotely observed deposits. Tools are not available to model the optical effects of the unusual geometries of the ilmenite laths in the black beads, so we address their effects on spectra of the regional pyroclastic deposits using computational mixing. We find that model spectra of pure glass (as opposed to devitrified black beads) provide good matches to all three regions. Radiative transfer modeling predicts iron contents of 21, 20, and 17 wt% FeO for Aristarchus, Humorum, and Sulpicius Gallus, respectively, and suggests that all three regions are low in titanium, a result supported by Lunar Prospector neutron spectrometer data. However, we find that a moderate Ti glass mixed with a small fraction of black beads cannot be ruled out for the Sulpicius Gallus region.

Big returns on small samples: Lessons learned from the analysis of small lunar samples and implications for the future scientific exploration of the Moon

Samples returned from the surface of planetary bodies are both complementary to orbital and in situ observations and provide a unique perspective for understanding the nature and evolution of that body. This unique perspective is based on the scale the sample is viewed (mm–Å), the ability to manipulate the sample, the capability to analyze the sample at high precision and accuracy, and the ability to significantly modify experiments as logic and technology dictates over an extended period of time (decades). Unlike the Apollo missions, robotic sample return missions in the next decade will result in the return of relatively small sample mass. Such robotically returned samples are scientifically more valuable if they can be placed within a planetary context through orbital observations and if information concerning planetary-scale processes and conditions can be extracted from them. Conversely, samples give remotely sensed data ground truth. That is, they act as a “calibration standard” for these data allowing a much enhanced global view to be constructed. The Moon is an example that illustrates how information can be extracted from small samples and then extended to planetary and solar system scales. Three examples from the Moon illustrate this point. First, multi-analytical and experimental studies of minute (10–500 μm) glass beads representing near-primary magmas provide constraints on the composition and condition of the lunar mantle, the style of early planetary differentiation, the history and character of early mantle dynamics and melting, and the isolation of the lunar mantle from late-stages of lunar accretion. Second, trace element analysis of individual mineral grains via ion microprobe and isotopic analysis of small rock fragments representing some of the oldest and youngest periods of lunar magmatism illustrate their usefulness for both fingerprinting distinct episodes of lunar magmatism and reconstructing the evolution of lunar magmatism. Third, mechanisms for primitive planetary mantles degassing and volatile transport on airless bodies can be understood by the analysis of volatile coatings on glass and mineral fragments in the lunar regolith. As many of our insights about the Moon are based on samples that primarily were collected within a limited lunar terrain, our understanding of the Moon is somewhat biased. Future scientifically strategic sampling targets are young mare basalts (Roris basalt in Oceanus Procellarum), far-side mare basalts (Mare Moscoviense), large pyroclastic deposits and potential mantle xenoliths (Aristarchus plateau, Rima Bode) major unsampled crustal lithologies outside the Procellarum KREEP terrane (central peak in Tsiolkovsky crater, South-pole Aitken basin), basin and crater melt sheets (South-pole Aitken basin, Giordano Bruno) and H deposits in permanently shaded areas (South-pole Aitken basin). Sampling these locations would further our understanding of processes at work during the early evolution of the terrestrial planets, provide a comprehensive history of endogenous (e.g., primary volcanic degassing) and exogenous (e.g., solar wind, galactic cosmic rays, volatiles from comets) volatile reservoirs and volatile transport and would provide unique historical information about events and processes that affected the entire inner solar system, a record obscured on the Earth and Mars.

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.

Calculating iron contents of lunar highland materials surrounding Tycho crater from integrated Clementine UV‐visible and near‐infrared data

Optical properties of lunar surface materials are modified by exposure to the space environment, including bombardment by solar wind particles and micrometeorites. One of the main problems in the interpretation of lunar spectral observations is to separate the effects of exposure (“space weathering”) and those due to the composition of the soils (mainly iron and titanium content). Here we use Clementine near‐infrared (NIR) data to investigate this problem for highland‐type soils in the Tycho crater area. Our approach is based on the methods developed for an analysis of a mare region near Aristarchus Plateau [Le Mouélic et al., 2000]. We show that the systematic relationships between spectral parameters (1‐μm band depth and continuum slope), which were previously observed in a mare area with varying maturity degree, are also valid for highland‐type soils. This technique aimed at evaluating the iron content of the surface materials from Clementine UV‐visible (UVVIS) and near‐infrared data can therefore be applied globally. This approach complements the widely used method of Lucey and coworkers, which relies on the UV‐visible bands only. The proposed method relies mostly on band ratios. The iron map produced from this method is therefore less dependent on topography than the iron estimates obtained with UV‐visible data alone, where brightness is one of the controlling parameters. Therefore the proposed approach should be particularly useful at middle to high latitudes, where local topography generates large variations in brightness and therefore hampers the interpretation of iron maps produced from UV‐visible bands only.

Dark ring in southwestern Orientale Basin: Origin as a single pyroclastic eruption

A large, 154 km diameter dark annular ring, located in the southwestern part of the Orientale Basin along the Montes Rook ring, was first discovered and documented in Soviet Zond 8 images. Clementine UV‐visible multispectral data indicate that the dark ring consists of material similar to the pyroclastic glasses collected by the Apollo astronauts, with the glasses being more closely related to the orange glass beads that comprise the Aristarchus Plateau than to the crystallized black beads typical of Taurus‐Littrow. This implies relatively rapid cooling times for the eruption products. We propose that the dark ring is the manifestation of a pyroclastic eruption originating at a fissure vent, an elongate 7.5 km by 16 km depression, located near the center of the ring. The event producing the eruption began with a dike rapidly emplaced from subcrustal depths to within ∼3–4 km of the surface. The dike stabilized and degassed over ∼1.7 years to form an upper foam layer which then penetrated to the surface to cause an eruption, lasting ∼1–2 weeks. The eruption produced a ∼38 km high symmetrical spray of pyroclasts into the lunar vacuum at velocities of ∼350 to ∼420 m/s, and the pyroclastic material accumulated in a symmetrical ring around the vent. The geometry of eruption caused the deposits to accumulate preferentially in a ring representing the material ejected at 45°. The paucity of pyroclastic rings of this type on the Moon can be attributed to the low probability of a dike stalling at just the right depth (∼3–4 km) to create these eruption conditions. The detailed characteristics of this ring provide important new insight into the emplacement of pyroclastics in the more regionally continuous lunar dark mantle deposits, suggesting that their sources are dominated by effusive and Hawaiian‐style eruptions. The Orientale dark ring deposit has similarities to the pyroclastic rings on the Galilean satellite Io. Both the Orientale dark ring and Ionian eruptions involve acceleration of small particles to a high velocity in an expanding gas stream, silicate pyroclasts derived from the disrupted foam layer in the lunar case, and a mixture of silicate pyroclasts and “snowflakes” of condensing SO2 solids on Io. In both cases the silicate pyroclasts ejected from the vent are accelerated by the gas until they become decoupled and continue on ballistic trajectories controlled only by gravity. Differences in mass flux and cloud opacity between the Moon and Io are the direct result of the origin and mass fraction of the volatile phase: the accumulation of a magmatic foam layer on top of a silicate intrusion in the lunar case and the intimate mixing on Io of a steadily erupting magma and liquid SO2. The interpretation of the Orientale dark mantle ring as a pyroclastic eruption provides an alternative to the hypothesis that the dark ring represents the presence of an ancient pre‐Orientale impact structure and that the Orientale Basin cavity of excavation must therefore lie within the Outer Rook Mountain ring.

Discrimination between maturity and composition of lunar soils from integrated Clementine UV‐visible/near‐infrared data: Application to the Aristarchus Plateau

The reflectance spectrum of a lunar soil is mainly dominated by the composition and the degree of exposure to space weathering processes such as micrometeorite bombardment and solar wind implantation. The spectral alteration effects of space weathering should be removed for accurately investigating the composition of the lunar surface using remote sensing data. In this paper we show that the integration of the Clementine UV‐visible (UVVIS) and near‐infrared (NIR) channels provides an improved evaluation of the spectral alteration. The depth of the mafic absorption feature at 0.95 μm is also better defined by combining the UVVIS and NIR data. Laboratory spectra of lunar soil samples indicate that the continuum slope derived from the 1500/750 nm ratio is closely related to the concentration of fine‐grained submicroscopic iron (Is). The continuum slope therefore provides an evaluation of the spectral alteration of the surface, which can be subtracted from the 1 or 2 μm absorption band depths to retrieve compositional information. This method has been applied to the Aristarchus plateau, which exhibits a broad range of mineralogical composition and maturity. A nine‐channel multispectral mosaic of 680 Clementine images of the Aristarchus plateau has been processed. Eight telescopic spectra have been used to check the validity of the reduction process for the near infrared bands. The 1 μm absorption band, once corrected for spectral alteration, provides an evaluation of the initial FeO content in mafic silicates (mafic iron). Lunar soil samples show that it is possible to quantitatively map mafic iron with this technique. Our results are in good agreement with those obtained using the algorithm of Lucey et al. [1995,1998a], which is based on UVVIS bands alone. The mafic iron content and total iron content which can be derived from the combined UVVIS and NIR data sets are less sensitive to local slopes than that derived from Lucey et al.'s method. This new method could therefore be useful for investigating areas at middle to high latitudes. Removing spectral alteration from the 2000/1500 nm ratio also makes possible a better discrimination between olivine and pyroxene within identified mare basalts on the Aristarchus plateau.

Compositional analyses of small lunar pyroclastic deposits using Clementine multispectral data

Clementine ultraviolet‐visible (UVVIS) data are used to examine the compositions of 18 pyroclastic deposits (15 small, three large) at 13 sites on the Moon. Compositional variations among pyroclastic deposits largely result from differing amounts of new basaltic (or juvenile) material and reworked local material entrained in their ejecta upon eruption. Characterization of pyroclastic deposit compositions allows us to understand the mechanisms of lunar explosive volcanism. Evidence for compositional differences between small pyroclastic deposits at a single site is observed at Atlas crater. At all sites, compositional variation among the small pyroclastic deposits is consistent with earlier classification based on Earth‐based spectra: three compositional groups can be observed, and the trend of increasing mafic absorption band strength from Group 1 to Group 2 to Group 3 is noted. As redefined here, Group 1 deposits include those of Alphonsus West, Alphonsus Southeast, Alphonsus Northeast 2, Atlas South, Crüger, Franklin, Grimaldi, Lavoisier, Oppenheimer, Orientale, and Riccioli. Group 1 deposits resemble lunar highlands, with weak mafic bands and relatively high UV/VIS ratios. Group 2 deposits include those of Alphonsus Northeast 1, Atlas North, Eastern Frigoris East and West, and Aristarchus Plateau; Group 2 deposits are similar to mature lunar maria, with moderate mafic band depths and intermediate UV/VIS ratios. The single Group 3 deposit, J. Herschel, has a relatively strong mafic band and a low UV/VIS ratio, and olivine is a likely juvenile component. Two of the deposits in these groups, Orientale and Aristarchus, are large pyroclastic deposits. The third large pyroclastic deposit, Apollo 17/Taurus Littrow, has a very weak mafic band and a high UV/VIS ratio and it does not belong to any of the compositional groups for small pyroclastic deposits. The observed compositional variations indicate that highland and mare materials are also present in many large and small pyroclastic deposits, and they suggest that volcanic glasses or spheres may not be dominant juvenile components in all large pyroclastic deposits.

Lunar regional dark mantle deposits: Geologic, multispectral, and modeling studies

Clementine five‐channel UV‐visible (UVVIS) data have been used to study seven regional dark mantle deposits (DMDs) on the Moon. The DMDs were mapped in distribution to determine their extent and stratigraphic relationship to other geologic units. Based upon the spectral properties for each DMD, the crystallization of the beads in each deposit was inferred and used to estimate cooling rates in the volcanic plumes that emplaced the deposits. Deposits with a high concentration of glasses reflect volcanic plumes that had low optical densities and high cooling rates, whereas deposits dominated by crystallized beads indicate plumes with slower cooling rates due to higher optical densities. Spectral data from each of the regional DMDs show that their glass:crystallized bead ratio can be estimated based upon their 415/750 and 750/950 nm values and comparison to laboratory spectra for the beads. Patches of young dark mantle in the Sinus Aestuum DMD represent one extreme with the bluest color (highest 415/750) and weakest glass band absorption (lowest 750/950) of all the DMDs. At the other extreme is the Aristarchus Plateau DMD with the reddest color and strongest glass band absorption. The other nearside DMDs, including Taurus‐Littrow, Sulpicius Gallus, Rima Bode, and Mare Vaporum lie between these two extremes due to intermediate mixtures of the crystallized beads and glasses with other local soils. The Orientale Ring DMD on the western limb is dominated by volcanic glasses and is spectrally similar to the localized DMDs found in Alphonsus crater. We have identified a central vent for the Orientale Ring DMD and model the eruption as degassing of a near‐surface dike to produce a 20‐km‐high umbrella‐shaped plume with ejection velocities of 360 m/s and deposition of the glasses at an average radius of 80 km from the vent. Although we cannot identify the exact sources for the other regional DMDs (probably because they are buried beneath younger mare), the eruptions most likely resulted from dikes breaching the surface and producing a volcanic plume dominated by larger (greater than submillimeter) hot clasts that formed mare and sinuous rules. The small percent of clasts that form the volcanic beads are carried by the expanding gas cloud to large distances, in some cases &gt;100 km, to produce the observed continuous regional DMDs. The lack of basalt samples that can be petrologically related to the volcanic glasses may be a result of their spatial separation, with the basalts flowing into the basins while the beads are deposited both into the basins and on the adjacent highlands.

Imaging spectroscopy of the moon: data reduction-analysis techniques and compositional variability of the Mare Serenitatis-Tranquillitatis region

In this paper we present some data concerning the lunar surface, obtained using a 0.4–1.1 μm imaging spectrometer at the Institute of Astrophysics of Andalucia 1.5m telescope in the Sierra Nevada Observatory. The data set consists of 16 image cubes (approximately 500,000 spectra) covering different lunar regions. Most of the areas imaged concern zones where red spots have been reported by previous authors (Whitaker, 1972; Bruno et al., 1991). They include Aristarchus plateau, Alphonsus, Gambart and Plato craters; Mare Serenitatis was also observed in order to calculate the spectral reflectance from the raw data. In this work we present the procedures we applied to analyze this set of data and we compare our results with those obtained by means of traditional techniques. In particular, we have studied the Mare Serenitatis-Mare Tranquillitatis region using statistical procedures with the objective of obtaining compositional maps. Using the principal component technique, the different composition of maria and highlands is revealed, and fresh craters against the underlying soil become apparent. A clustering technique allowed us to distinguish six spectrally different areas within the study region.

Imaging spectroscopy of the Moon: A study of the Aristarchus region

In this paper we present some results concerning the Aristarchus plateau and Mounts Harbinger regions. The study was conducted using an imaging spectrometer in the 0.4–1.1 μm spectral range at the 1.5 meters Sierra Nevada Observatory telescope. We report the albedo, the UV-VIS continuum and 0.9–1 μm absorption band maps, showing the complex pattern of Aristarchus crater ejecta and the distribution of surrounding materials. The extension of the dark mantling deposits present on Aristarchus plateau is well shown from our data, appearing very red and with a uniform distribution of the 0.9–1 μm band.

Clementine Observations of the Aristarchus Region of the Moon

Multispectral and topographic data acquired by the Clementine spacecraft provide information on the composition and geologic history of the Aristarchus region of the moon. Altimetry profiles show the Aristarchus plateau dipping about 1 degrees to the north-northwest and rising about 2 kilometers above the surrounding lavas of Oceanus Procellarum to the south. Dark, reddish pyroclastic glass covers the plateau to average depths of 10 to 30 meters, as determined from the estimated excavation depths of 100- to 1000-meter-diameter craters that have exposed materials below the pyroclastics. These craters and the walls of sinuous rilles also show that mare basalts underlie the pyroclastics across much of the plateau. Near-infrared images of Aristarchus crater reveal olivine-rich materials and two kilometer-sized outcrops of anorthosite in the central peaks. The anorthosite could be either a derivative of local magnesium-suite magmatism or a remnant of the ferroan anorthosite crust that formed over the primordial magma ocean.