Dark Mantle Research Articles

Volcanic glass signatures in spectroscopic survey of newly proposed lunar pyroclastic deposits

Moon Mineralogy Mapper spectroscopic observations are used to assess the mineralogy of five sites that have recently been proposed to include lunar dark mantle deposits (DMDs). Volcanic glasses have, for the first time, clearly been identified at the location of three of the proposed pyroclastic deposits. This is the first time that volcanic glasses have been identified at such a small scale on the lunar surface from remote sensing observations. Deposits at Birt E, Schluter, and Walther A appear to be glassy DMDs. Deposits at Birt E and Schluter show (1) morphological evidence suggesting a likely vent and (2) mineralogical evidence indicative of the presence of volcanic glasses. The Walther A deposits, although they show no morphological evidence of vents, have the spectroscopic characteristics diagnostic of volcanic glasses. The deposits of the Freundlich-Sharonov basin are separated in two areas: (1) the Buys-Ballot deposits lack mineralogical and morphological evidence and thus are found to be associated with mare volcanism not with DMDs and (2) the Anderson crater deposits, which do not exhibit glassy DMD signatures, but they appear to be associated with possible vent structures and so may be classifiable as DMDs. Finally, dark deposits near the crater Kopff are found to be associated with likely mare volcanism and not associated with DMDs. The spectral identification of volcanic glass seen in many of the potential DMDs is a strong indicator of their pyroclastic origin.

A new type of pyroclastic deposit on the Moon containing Fe‐spinel and chromite

We present details of the identification of sites that show an absorption band at visible wavelengths and a strong 2 μm band using the SELENE Spectral Profiler. All the sites exhibiting the visible feature are found on the regional dark mantle deposit (DMD) at Sinus Aestuum. All the instances of the visible feature show a strong 2 μm band, suggestive of Fe‐ and Cr‐rich spinels, which are different from previously detected Mg‐rich spinel. Since no visible feature is observed in other DMDs, the DMD at Sinus Aestuum is unique on the Moon. The occurrence trend of the spinels at Sinus Aestuum is also different from that of the Mg‐rich spinels, which are associated with impact structures. This may suggest that the spinel at Sinus Aestuum is a different origin from that of the Mg‐rich spinel.

Mineralogy and stratigraphy of phyllosilicate‐bearing and dark mantling units in the greater Mawrth Vallis/west Arabia Terra area: Constraints on geological origin

Analyses of MRO/CRISM images of the greater Mawrth Vallis region of Mars affirm the presence of two primary phyllosilicate assemblages throughout a region ∼1000 × 1000 km. These two units consist of an Fe/Mg‐phyllosilicate assemblage overlain by an Al‐phyllosilicate and hydrated silica assemblage. The lower unit contains Fe/Mg‐smectites, sometimes combined with one or more of these other Fe/Mg‐phyllosilicates: serpentine, chlorite, biotite, and/or vermiculite. It is more than 100 m thick and finely layered at meter scales. The upper unit includes Al‐smectite, kaolin group minerals, and hydrated silica. It is tens of meters thick and finely layered as well. A common phyllosilicate stratigraphy and morphology is observed throughout the greater region wherever erosional windows are present. This suggests that the geologic processes forming these units must have occurred on at least a regional scale. Sinuous ridges (interpreted to be inverted channels) and narrow channels cut into the upper clay‐bearing unit suggesting that aqueous processes were prevalent after, and possibly during, the deposition of the layered units. We propose that layered units may have been deposited at Mawrth Vallis and then subsequently altered to form the hydrated units. The Fe/Mg‐phyllosilicate assemblage is consistent with hydrothermal alteration or pedogenesis of mafic to ultramafic rocks. The Al‐phyllosilicate/hydrated silica unit may have formed through alteration of felsic material or via leaching of basaltic material through pedogenic alteration or a mildly acidic environment. These phyllosilicate‐bearing units are overlain by a darker, relatively unaltered, and indurated material that has probably experienced a complex geological history.

A new view of dark Martian regions from geomorphic and spectroscopic analysis of Syrtis Major

New analysis of Mars Observer Camera (MOC) images and Thermal Emission Imaging System (THEMIS) data focussed on West Syrtis Major show that this region, usually interpreted as typical of in-situ bedrocks, is covered by a dark mantle which could result from a transient deposition of suspended fine particles still active until a few million years ago. To help address the questions of the nature of these low albedo regions covered by blankets, we revisited the surface composition by modelling Imaging Spectrometer (ISM) spectra with a radiative transfer model, the strength of such a modelling method being to aid in determining appropriate endmembers as well as their relative abundance, their grain size, and the type of mixtures (sand/dust). Two distinct surface compositions (basaltic sand vs. sand/dust mixture of pyroxenes and oxides) are possible. The solution more consistent with the geomorphic analysis is the sand/dust mixture with a large proportion of dusty grains of oxides and/or pyroxenes (about 50-60%). This implies that Type 1 plagioclase-rich lithology derived from Thermal Emission Spectrometer (TES) is not required by NIR data. This work gives new evidence of the presence of dark dust on the surface of Mars.

Remote sensing studies of the Lomonosov‐Fleming region of the Moon

Lomonosov‐Fleming is a 620 km, pre‐Nectarian impact basin centered at 19°N, 105°E. Clementine multispectral images and a variety of spacecraft photographs were used to investigate the composition and origin of geologic units in the region. Mare basalt deposits in the Lomonosov‐Fleming region are small and exhibit varying degrees of highlands contamination. Four previously unrecognized dark mantle deposits of probable pyroclastic origin were identified and mapped. A major expanse of cryptomare was mapped in and around the Lomonosov‐Fleming basin. Spectral and chemical data obtained for dark‐haloed craters (DHC) established that these impact craters excavated mare basalt from beneath higher‐albedo highlands‐rich surface units. The buried basalts exposed by DHCs in the region exhibit a variety of compositions, which range from very low titanium basalt to intermediate TiO2 mare basalt. Nectarian‐aged units with subjacent cryptomare are much more extensive than Imbrian‐aged deposits with underlying basalt. At least some of the buried mare basalts in the region may have been emplaced during pre‐Nectarian time. While both impact basins and craters played a role in cryptomare formation by transporting highlands material to mare surfaces, the evidence indicates that most of the cryptomare inside the basin are of the distal basin ejecta type. The enhanced FeO and TiO2 abundances exhibited by these cryptomare surfaces, usually light plains units, demonstrate that ballistic erosion and sedimentation played an important role in their formation.

Highland contamination in lunar mare soils: Improved mapping with multiple end‐member spectral mixture analysis (MESMA)

Multiple end‐member spectral mixture analysis (MESMA) was applied to the Clementine UVVIS global 1 km multispectral data set, and the resulting highland material fraction image was used to investigate highland contamination of mare surfaces by impact cratering. MESMA decomposes each pixel with the number of end‐members fewer than the number of the spectral bands of Clementine UVVIS data. This allows the use of variable end‐member combinations to accommodate global spectral variance. A 13‐end‐member set of lunar soil components that spans the lunar spectral diversity was selected from the UVVIS data and included 1 mature and 4 fresh highland soils, 4 mature and 2 fresh mare soils, and 2 soils of dark mantling materials. This set was applied to the lunar data through MESMA, and an aggregated global highland abundance was derived. Comparison of the highland fraction results from MESMA and traditional spectral mixture analysis (SMA) demonstrated that MESMA better accommodates the compositional variation of mare soils, resulting in a greater accuracy in the measurement of highland. With the derived products, we investigated highland contamination in Mare Nectaris, Mare Fecunditatis, and Mare Crisium. These mare surfaces are proximal to the large craters Theophilus, Taruntius, Langrenus, and Proclus and provided an opportunity to investigate highland contamination by large impacts. The analyses indicated that Theophilus impact resulted in highland contamination of 20–80% on most of Mare Nectaris, while Taruntius and Langrenus impacts caused 5–40% contamination of Mare Fecunditatis. The trend of minimal highland abundance in Mare Fecunditatis correlates poorly with basalt thickness, suggesting an efficient lateral mixing due to the large craters Taruntius and Langrenus. Additionally, Proclus, combining with other craters, was responsible for highland contamination in most of the Mare Crisium surface, and some basalt classification in this mare reflects highland contamination of the spectral properties. MESMA significantly reduces uncertainty in calculating global composition variations due to mixing, and these analyses demonstrate that large impacts played a dominant role in delivering highland materials onto three mare surfaces.

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.

The Morphology of Small Craters and Knobs on the Surface of Jupiter's Satellite Callisto

Using the images of Callisto's surface acquired at 15-km resolution by the Galileo spacecraft during its C21 orbit, we studied the morphology of craters with diameters of less than 1–2 km and knobs. By analogy with other regions of Callisto that have been studied, these craters and knobs are thought to be formed by the sublimation degradation of the rims of larger craters that are also present in the region under study. The small craters closely resemble similar-sized lunar craters and, by analogy with the latter, are also divided into morphological classes. The depths of 42 craters of different morphological classes are estimated using shadow lengths visible in the craters. The fractions of the craters of different classes in the subpopulation are determined as a function of the crater diameter. Evidence has been obtained that larger craters degrade at a slower rate than smaller ones. The mean thickness of the mantle of dark material (∼40 m) is estimated from the sizes of the craters ejecting the blocks of the basement ice material. The shape of the knob shadows shows that the knobs are heights of mostly conical form with slopes whose steepness is close to the angle of repose. Analysis has shown that the observed landforms and material units of the region under investigation have been formed during two successive stages of the geologic history of Callisto. Large craters, knobs, and the mantle of dark material were formed mostly at the end of the period of heavy meteorite bombardment. The leading processes of this period are impact cratering, the sublimation of Callisto's “crustal” ice with the accumulation of residual non-icy material, and downslope mass movement. The next stage, which continues until the present time, involved the formation of the subpopulation of small (<1–2 km) craters. This formation was accompanied by the impact reworking of the upper portion of the dark mantle. The key processes occurring at this stage are impact cratering and downslope mass movement. The mean intensity of resurfacing at this stage is much lower than at the preceding stage.

Imaging spectroscopy of selected regional dark mantle deposits of the Moon

We present the study of four surface units previously identified as dark mantle deposits on the Moon: Taurus Littrow, Sulpicius Gallus, Mare Vaporum and Rima Bode deposits. The data have been obtained at the 1.5 m telescope of Sierra Nevada Observatory (Granada, Spain) by using an imaging spectrometer working in the 0.4– 1.0 μm spectral range. Principal features of these geologic units are: (a) low albedo, (b) localization at the boundaries between highlands and maria, and (c) spectral properties similar to those of the associated mare lavas. The image cubes have been processed by means of two independent statistical methods: the principal components analysis and a supervised clustering technique (spectral angle mapper). Using these methods it has been possible to identify the areas covered by dark mantling material and to compare the different spectral properties of the four deposits. In particular, two different classes of the dark mantle deposits have been detected on the basis of the spectra. New areas in Sulpicius Gallus deposit having intermediate spectral behavior between highland soil and dark mantling material have been identified, probably due to a mixing of the two terrains.

Spectral properties of the Marius Hills volcanic complex and implications for the formation of lunar domes and cones

We have used multispectral data from the Clementine UV‐visible camera to study the volcanic features of the Marius Hills complex and their comparison to other lunar domes and cones. There are several mare units identified in the complex, each with a unique Ti content, as indicated by their 415/750 nm value. The domes in Marius Hills are spectrally identical to the mare plains of the complex, supporting similar compositions. In contrast, most of the volcanic cones of the complex are lower in reflectance, bluer in color, and have weaker mafic absorptions than the mare and domes. The spectral characteristics of the cones can best be explained by fine‐grained crystallization in the spatter that compose the cones. Other lunar cones, such as Mons Esam in northern Tranquillitatis, have spectral properties similar to those at Marius Hills. The Rima Parry cones and their associated dark mantle deposit appear redder with a stronger mafic absorption than the Marius Hills cones. The cones Isis and Osiris in southern Mare Serenitatis, the domes of Rumker Hills, and several domes in northern Mare Tranquillitatis are spectrally similar to adjacent mare units. The Mairan and Gruithuisen domes in northern Oceanus Procellarum have a feldspathic signature characteristic of highland material although they are redder and brighter than adjacent highland soils. They appear to represent highland material that resembles domes rather than actual mare domes, like those at Marius and Rumker Hills. The diversity of lunar volcanic features can best be explained by differences in accumulation rates and cooling of ejected clasts from various eruption styles. Mare domes may have formed at lower effusion rates, thereby allowing lava to construct small shields with slopes &lt;3°. The steeper domes at Marius Hills require higher viscosities resulting from even lower effusion rates and enhanced crystallization in the magmas during the terminal stages of earlier eruptions that emplaced the mare. Cones like Mons Esam, Rima Parry, Isis, and Osiris are aligned along linear rules and are interpreted to result from degassing of near‐surface dikes. In contrast, the cones of Marius Hills show no linear alignment and may result from strombolian eruptions at the terminal stages of earlier effusive eruptions that emplaced the domes and mare in the complex.

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: 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.

Crustal diversity of the moon: Compositional analyses of Galileo solid state imaging data

The multispectral images of the lunar limb and farside obtained by the solid state imaging (SSI) system on board the Galileo spacecraft provide the first new pulse of compositional data of the Moon by a spacecraft in well over a decade. The wavelength range covered by SSI filters (0.4–1.0 μm) is particularly sensitive to the composition of mare basalts, the abundance of mafic (ferrous) minerals, and the maturity of the regolith. To a first order, the limb and farside material is consistent with previous characterization of nearside lunar spectral types for mare and highland soils and craters. Most basalts are of an intermediate TiO2 composition and most of the highland crust is feldspathic with local variations in mafic content identified principally at impact craters. Dark mantling material on the farside can be interpreted in terms of known properties of lunar pyroclastic glass. Regions of cryptomare are shown to have spectral properties intermediate between those of highland and mare soils, as would be expected from a mixture of the two. There are several important exceptions and surprises, however. Unlike the basalt types identified on the nearside, limb and farside basalts exhibit an exceptionally weak 1 μm ferrous absorption band. This may indicate a compositionally distinct lunar basalt group that, for example, is more Mg‐rich than most basalts of the nearside. Some of the most notable compositional anomalies are associated with South Pole‐Aitken Basin. This large region has a much lower albedo than surrounding highlands. The inner, darkest, portion of the basin exhibits optical properties indistinguishable from low‐Ti basalts. Deposits to the south exhibit unique properties with a strong and broad ferrous 1 μm absorption, most consistent with abundant olivine. The unusual compositions associated with South Pole‐Aitken and their spatial extent suggests the impact creating this huge lunar basin excavated mafic‐rich lower crust or perhaps mantle material.

Galileo imaging observations of lunar maria and related deposits

The Galileo spacecraft imaged parts of the western limb and far side of the Moon in December 1990. Ratios of 0.41/0.56 μm filter images from the Solid State Imaging (SSI) experiment provided information on the titanium content of mare deposits; ratios of the 0.76/0.99 μm images indicated 1 μm absorptions associated with Fe2+ in mafic minerals. Mare ages were derived from crater statistics obtained from Lunar Orbiter images. Results on mare compositions in western Oceanus Procellarum and the Humorum basin are consistent with previous Earth‐based observations, thus providing confidence in the use of Galileo data to extract compositional information. Mare units in the Grimaldi and Riccioli basins range in age from 3.25 to 3.48 Ga and consist of medium‐ to medium‐high titanium (&lt;4 to 7% TiO2) content lavas. The Schiller‐Zucchius basin shows a higher 0.76/0.99 μm ratio than the surrounding highlands, indicating a potentially higher mafic mineral content consistent with previous interpretations that the area includes mare deposits blanketed by highland ejecta and light plains materials. The oldest mare materials in the Orientale basin occur in south‐central Mare Orientale and are 3.7 Ga old; youngest mare materials are in Lacus Autumni and are 2.85 Ga old; these units are medium‐ to medium‐high titanium (&lt;4 to 7% TiO2) basalts. Thus, volcanism was active in Orientale for 0.85 Ga, but lavas were relatively constant in composition. Galileo data suggest that Mendel‐Rydberg mare is similar to Mare Orientale; cryptomare are present as well. Thus, the mare lavas on the western limb and far side (to 178°E) are remarkably uniform in composition, being generally of medium‐ to medium‐high titanium content and having relatively low 0.76/0.99 μm ratios. This region of the Moon is between two postulated large impact structures, the Procellarum and the South Pole‐Aitken basins, and may have a relatively thick crust. In areas underlain by an inferred thinner crust, i.e., zones within large basins (as at Apollo), titanium content is often higher. However, no mare deposits with titanium abundances approaching those of the high‐titanium (9 to 14% TiO2) Apollo 11 and 17 basalts nor of the high‐titanium regions of central Oceanus Procellarum are seen on the western limb or eastern far side. Light plains deposits are generally indistinct from the surrounding highlands in the SSI data and are inferred to be derived primarily from the same material that forms the highlands. Some of the light plains are too young to be related to basin‐forming impacts, suggesting possible volcanic origin. Dark mantle deposit compositions derived from SSI data are consistent with Earth‐based observations of similar near‐side deposits and are interpreted to be pyroclastic materials. However, the moderate albedo and 1 μm absorption of the dark mantle deposit on the southwest margin of the Orientale basin suggest it is a local pyroclastic deposit contaminated with underlying highland materials from the Orientale impact.

Remote sensing of potential lunar resources: 1. Near‐side compositional properties

New telescopic CCD multispectral imaging of the lunar near side and 330–870 nm spectroscopy of selected regions are presented as aids in estimating compositional differences relevant to locating potential lunar resources such as ilmenite (FeTiO3) and solar wind‐implanted 3He and H. Conversion of 400/560 nm CCD ratio images to weight percent TiO2 using a version of the Charette et al. (1974) empirical relation allows construction of a new TiO2 abundance map for the lunar maria accurate to ±2 wt % HO2. This map provides a consistent view of TiO2 distribution among mature mare soils and can be used to estimate areas potentially rich in ilmenite. Western Mare Tranquillitatis exhibits the highest TiO2 abundances (&gt;8 wt %), followed by regions near Flamsteed P and in northern Oceanus Procellarum. A 950/560 nm CCD ratio mosaic of the full Moon provides estimates of relative surface maturity on local scales as defined by the degree of agglutinate production due to micrometeorite impacts. Since high 3He concentrations are correlated with mature ilmenite‐rich soils, a combination of relative surface maturity maps and TiO2 abundance maps may be useful for estimating 3He (and possibly H) distribution on local scales. While dark mantle materials are also potential sources of ilmenite, 3He, and H, their compositional differences from mare soils prevent accurate remote mapping of their TiO2 abundance and relative maturity. Reflectance spectra (relative to a more rigorously defined MS‐2 standard region) of dark mantle materials and high‐TiO2 mare areas exhibit previously undocumented near‐UV (&lt;350 nm) changes in spectral slope apparently related to compositional variations. Determination of the primary lunar sites for resource utilization will be dictated by the future goals and priorities of the lunar resource program.

Moon: Near‐infrared spectral reflectance, A first good look

A positive identification of the minerals olivine, plagioclase, and several types of pyroxenes were made at several locations on the lunar surface by using remote measurements. For example, the crater Aristarchus is found to have an average pyroxene composition of augite, and plagioclase is obviously present. A dark mantle deposit in the crater J. Herschel is at least partly composed of a mixture of 70% olivine and 30% pyroxene. These determinations were possible because the reflectance spectra for 10–20 km diameter lunar areas have been measured for the first time in the IR spectral region (0.65–2.5 μm) with sufficient spectral resolution and photometric precision to define mineral electronic absorption bands. The reflectance for all lunar regions observed (over 100 to present) continues to increase toward longer wavelengths to at least 2.5 μm, and several mineral absorption bands appear. The telescopic spectra are of similar quality and contain features similar to laboratory spectra of lunar samples. The absorption features in several spectra have been quantitatively analyzed using newly developed computer processing techniques, including thermal flux removal and absorption band fitting, to produce these mineral identifications. Detection and quantitative analysis of these absorptions provide a much improved basis for remotely determining and mapping surface mineralogy quantitatively from the ground or using airborne or spacecraft platforms.

Ascent and eruption of basaltic magma on the Earth and Moon

Geological and physical observations and constraints are applied to the development of a model of the ascent and emplacement of basaltic magma on the earth and moon. Mathematical models of the nature and motion of gas/liquid mixtures are developed and show that gas exsolution from terrestrial and lunar magmas commonly only occurs at shallow depths (less than 2 km); thus the ascent of bubble‐free magma at depth can be treated separately from the complex motions caused by gas exsolution near the surface. Magma ascent is related to dike or conduit width; a lower limit to width is determined by the presence of a finite magma yield strength or by excessive magma cooling effects related to magma viscosity. For terrestrial basalts with negligible yield strengths and viscosities greater than 102 Pa s, widths in the range 0.2–0.6 m are needed to allow eruptions from between depths of 0.5–20 km. Fissure widths of about 4 m would be needed to account for the output rates estimated for the Columbia River flood basalt eruptions. As the magma nears the surface, bubble coalescence will tend to occur, leading to intermittent explosive strombolian‐style activity. For commonly occurring lunar and terrestrial basalts the magma rise speed must be greater than 0.5–1 m/s if strombolian activity is to be avoided and relatively steady fire fountaining is to take place. Terrestrial fire fountain heights are dictated by the vertical velocity of the magma/gas dispersion emerging through the vent, increasing with increasing magma gas content and mass eruption rate, and decreasing with increasing magma viscosity. Terrestrial fire fountain heights up to 500 m imply the release of up to 0.4 wt % water from the magma, corresponding to initial water contents up to 0.6 wt %. The presence of extremely long lava flows and sinuous rules on the moon has often been cited as evidence for very high extrusion rates and thus a basic difference between terrestrial and lunar magmas and crustal environments. However, the differences between terrestrial and lunar magma rheologies and crustal environments do not lead to gross differences between the effusion rates expected on the two planetary bodies, for similar‐sized conduits or fissures. Thus the presence of these features implies only that tectonic and other forces associated with the onset of some lunar eruptions were such as to allow wide fissures or conduits to form. The surface widths of elongate fissure vents need be no wider than 10 m to allow mass eruption rates up to 10 times larger than those proposed for terrestrial flood basalt eruptions; 25‐m widths would allow rates 100 times larger. It therefore appears unlikely that source vents on the moon with widths greater than a few tens of meters represent the true size of the unmodified vent. The main volatile released from lunar magmas was probably carbon monoxide, released in amounts proportionally less than terrestrial magmas by more than an order of magnitude. However, decompression to the near‐zero ambient lunar atmospheric pressure causes much greater energy release per unit mass and this, coupled with vertical and horizontal expansion of the gas, suggests a much more efficient use of the available gas on the moon than on the earth. Some amount of magma disruption must always have taken place in lunar eruptions unless the gas content was truly zero or the magma possessed an appreciable yield strength. Pyroclastic deposits, such as the extensive lunar dark mantling material, could be produced from a single source vent and extend to diameters of up to 200 km. Such deposits could result either from steady eruptions at high effusion rates (with less than 1% of the magma disrupted into submillimeter droplets) or low effusion rate eruptions in which strombolian activity occurred. The wide dispersal of pyroclastic debris is a result of small particles being locked into the expanding gas cloud. Finally, we consider the details of basaltic eruption processes on the moon and predict the nature and geometry of several types of volcanic landforms (flows, pyroclastic blankets and cones, cinder and spatter ridges, etc.) that should result from specific eruption conditions.

Late high‐titanium basalts of the Western Maria: Geology of the Flamsteed REgion of Oceanus Procellarum

The Flamsteed region of Oceanus Procellarum is representative of an unsampled volcanic complex on the lunar nearside. The evolution of this region, as portrayed in the current surface, is investigated in detail. A synthesis of remote sensing data, including multispectral images (digital vidicon images and color composite photographs), spectral reflectance measurements, radar topographic maps, and orbital and earth‐based photography, is presented. Additional information is derived from crater degradation studies, radar backscatter, gravity measurements and orbital γ ray data. Seven spectrally distinct basaltic units, which range in age from 2.5±0.5 b.y. to 3.65±0.15 b.y., have been identified. Three have been formally named and related to the Procellarum lithostratigraphic nomenclature scheme. The earliest units within the mapped area are composed of highlands material and include partially flooded impact craters. Another early nonmare unit is spectrally distinct material that occurs as plains and domes and which, in part, is of probable extrusive origin. Small amounts of dark mantle material suggest the presence of an early Ti‐rich basalt (Repsold Formation) beneath the presently exposed mare basalts. The oldest surface exposed mare basalts are very low Ti basalts of the Telemann Formation. These are overlain by low to intermediate Ti basalts of the Hermann Formation. The youngest exposed basalts are the moderately Ti‐rich members of the Sharp Formation. The unsampled Flamsteed basalt, a young Ti‐rich unit defined here, is comparable to Apollo 11 basalts in many measurable parameters except the strength of an absorption feature at 1 μm. This distinction implies a fundamental difference in mineralogy of the two titanium‐rich units; the Flamsteed basalts may be more iron rich than the other lunar basalts. The total mare fill in the Flamsteed region is probably of the order of 400‐m average thickness. Ejecta from young craters such as Kepler and Copernicus overlie some basalts. The major deformation of these units, evidenced by tectonic rules and mare ridges, terminated prior to the emplacement of the youngest mare unit during the emplacement of the Hermann Formation. This complexity of emplacement history and wide variety of observed basalt types, largely unsampled by Apollo and Luna missions, provide additional details of basaltic volcanism on the moon and require models of lunar basalt petrogenesis to be reexamined.

Oxidative stabilization of acrylic fibres

When acrylic fibres are heat treated for various times at 220 to 250° C, they form dark, insoluble structures of uncertain chemical character which are inert to many strong oxidizing and reducing agents. The heat-treated fibres are, however, rapidly decoloured by warm alkaline hypochlorite solutions. When fibres which have undergone short-time heat treatment are subjected to the hypochlorite, incubation periods are observed before decolouration is noted; and a swollen acrylic network remains after decolouration is complete. The acrylic network is primarily unreacted precursor units save for a small amount of hydrolyzed material. The decoloured reaction is zero order, indicating a reaction at the surface. The rate of the decolouration reaction also increases with increasing duration of the stabilization heat treatment. In fibres which have undergone partial diffusion-controlled stabilization, a dark mantle surrounds a lightly coloured core. The rate of decolouration is unaffected as the decolouration interface passes from the mantle to the core, indicating that the decolouration reaction is not influenced by the occurance of any sequent reactions. The existence of the acrylic residue indicates that the prefatory reactions are continuing in both mantle and core during the course of stabilization.13C-NMR spectra of the acrylic residue show the same triad methine peak areas as those obtained on the untreated fibre; hence the stereoregularity of the nitrile groups has no influence on the rate of nitrile polymerization. The mechanisms of nitrile initiation and of decolouration are discussed. The residue obtained by sulphuric acid etch is different from that obtained by hypochlorite treatment. These results suggest that during the early-to-intermediate stages of stabilization, the fibre consists of interpenetrating networks of original material, i.e., fibre which has undergone only the prefatory reactions and fibre which has undergone the sequent reactions.

The Aristarchus-Harbinger region of the moon: Surface geology and history from recent remote-sensing observations

The region including the Aristarchus Plateau and Montes Harbinger is probably the most diverse, geologically, of any area of comparble size on the Moon. This part of the northwest quadrant of the lunar near side includes unique dark mantling material; both the densest concentration and the largest of the sinuous rilles; apparent volcanic vents, sinks, and domes; mare materials of various ages and colors; one of the freshest large craters (Aristarchus) with ejecta having unique colors and albedos; and three other large craters in different states of flooding and degradation (krieger, Herodotus, and Prinz). The three best-authenticated lunar transient phenomena were also observed here. This study is based principally on photographic and remote sensing observations made from Earth and Apollo orbiting space craft. Results include (1) delineation of geologic map units and their stratigraphic relationships; (2) discussion of the complex interrelationships between materials of volcanic and impact origin, including the effects of excavation, redistribution and mixing of previously deposited materials by younger impact craters; (3) deduction of physical and chemical properties of certain of the geologic units, based on both the remote-sensing information and on extrapolation of Apollo data to this area; and (4) development of a detailed geologic history of the region, outlining the probable sequence of events that resulted in its present appearance. A primary concern of the investigation has been anomalous red dark mantle on the Plateau. Based on an integration of Earth- and lunar orbit-based data, this layer seems to consist of fine-grained, block-free material containing a relatively large fraction of orange glass. It is probably of pyroclastic origin, laid down at some time during the Imbrian period of mare flooding.