Mineralogy of northern nearside mare basalts

The mineralogy of mare basalts reflects the chemical composition of the magma source, as well as the physical and chemical environment of the rocks' formation. This is significant for understanding the thermal evolution of the Moon. In this study, the spatial distribution of mineralogy on the lunar northern nearside basalts was mapped using the Moon Mineralogy Mapper(M^3) data. The study area, which is an elongated mare, Mare Frigoris and northern Mare Imbrium, was mapped and characterized into 27 units based on multi-source data, including spectrum, terrain and element abundance. We extracted 177 M^3 spectra from fresh craters. Spectral parameters such as absorption center and band area ratio(BAR)were obtained through data processing. The variation of mafic minerals in this region was acquired by analyzing these parameters. The basaltic units in eastern Mare Frigoris, which are older, have been found to be dominated by clinopyroxene with lower CaO compared to the returned lunar samples; this is similar to older basaltic units in Mare Imbrium. The basaltic units of western Mare Frigoris and Sinus Roris which are younger have been found to be rich in olivine. The late-stage basalts in Oceanus Procellarum and Mare Imbrium show the same feature. These widespread olivine-rich basalts suggest uniqueness in the evolution of the Moon. Geographically speaking, Mare Frigoris is an individual mare, but the magma source region has connections with surrounding maria in consideration of mineral differences between western and eastern Frigoris, as well as mineral similarities with maria at the same location.     

Lunar mare volcanism in the eastern nearside region derived from Clementine UV/VIS data

Abstract— Clementine UV/VIS multi‐spectral data were used to map mare deposits in the eastern lunar nearside region (Mare Tranquillitatis, Mare Fecunditatis, Mare Serenitatis, Mare Crisium, Mare Nectaris) to understand the volcanic history of this region. An array of Clementine and Clementine‐derived data were used to classify mare basalts; these include: 750 nm albedo, UV/VIS ratio, 1 μm absorption signatures, and Clementine derived FeO and TiO₂ contents. We have successfully identified several new geological units and have determined their spectral characteristics. For example, the relatively younger low‐Ti basalts were recognized in the eastern part of Mare Tranquillitatis. The central low‐Ti basalts in Mare Serenitatis, which had been classed as mISP, were divided into 2 groups. In Mare Nectaris, 2 types of mare basalts were identified, while only 1 group was recognized in the previous study. The stratigraphy constructed from the spectral analysis indicates that the mare deposits tend to become younger in the northern maria, including Serenitatis and Crisium, and older in the southern maria, including Tranquillitatis, Fecunditatis, and Nectaris. According to the relationship between the titanium contents of the mare units and their stratigraphy, the titanium content decreases with time in the early stage but increases toward the end of volcanism in the Serenitatis and Crisium region, while it increases with time but finally decreases in the Tranquillitatis and Fecunditatis region. In connection with the distribution of mare basalts, a large amount of high‐Ti mare basalts are found in Mare Tranquillitatis, especially in the western part, while other maria are covered by low‐Ti basalts. The iron contents show a similar distribution to that of titanium.     

Geologic context of in situ rocky exposures in Mare Serpentis, Mars: Implications for crust and regolith evolution in the cratered highlands

Global acquisition of infrared spectra and high-resolution visible and infrared imagery has enabled the placement of compositional information within stratigraphic and geologic context. Mare Serpentis, a low albedo region located northwest of Hellas Basin, is rich in spectral and thermophysical diversity and host to numerous isolated exposures of in situ rocky material. Most martian surfaces are dominated by fine-grained particulate materials that bear an uncertain compositional and spatial relationship to their source. Thus location and characterization of in situ rock exposures is important for understanding the origin of highland materials and the processes which have modified those materials. Using spectral, thermophysical and morphologic information, we assess the local and regional stratigraphy of the Mare Serpentis surface in an effort to reconstruct the geologic history of the region. The martian highlands in Mare Serpentis are dominated by two interspersed surface units, which have distinct compositional and thermophysical properties: (1) rock-dominated surfaces relatively enriched in olivine and pyroxene, and depleted in high-silica phases, and (2) sediment or indurated material depleted in olivine and pyroxene, with relatively higher abundance of high-silica phases. This is a major, previously unrecognized trend which appears to be pervasive in the Mare Serpentis region and possibly in other highland areas. The detailed observations have led us to form two hypotheses for the relationship between these two units: either (1) they are related through a widespread mechanical and/or chemical alteration process, where less-mafic plains materials are derived from the mafic bedrock, but have been compositionally altered in the process of regolith formation, or (2) they are stratigraphically distinct units representing separate episodes of upper crust formation. Existing observations suggest that the second scenario is more likely. In this scenario, plains materials represent older, degraded, and possibly altered, “basement” rock, whereas the rocky exposures represent later additions to the crust and are probably volcanic in origin. These hypotheses should be further testable with decimeter-resolution imagery and meter-resolution short wavelength infrared spectra.     

The Distribution of Craters Within Craters

Photometric correction is a necessary step in planetary image pre-processing since the images of planetary surfaces are acquired by orbiting spacecraft at various observational geometries. In this study, visible (748 nm) and near-infrared (948 nm) bands of Hyper Spectral Imager (HySI) onboard Chandrayaan-1 have been used to derive a preliminary photometric correction for lunar data. The purpose of the proposed photometric correction for HySI is to convert observations taken at solar incidence (i), sensor emission (e), and the solar phase angles (α) to a fixed geometry by applying i?=?α?=?30° and e?=?0° to each image. The Lommel–Seeliger function was used to model the lunar limb darkening effect, while topography data from the merged Digital Elevation Model of Lunar Reconnaissance Orbiter—Lunar Orbiter Laser Altimeter (LRO-LOLA) and SELENE Terrain Camera (TC) was used to correct local topographic effects. Data from Moon Mineralogy Mapper (M³), SELENE Multiband Imager (MI) and Clementine Ultraviolet and Visible Camera (UV/VIS) were also used to compare radiance, reflectance and phase functions derived from HySI. Our analysis reveals that HySI is darker than M³ primarily due to low surface radiance conditions observed by HySI. The derived phase functions for the two HySI bands indicate a good correlation between the derived reflectance and phase angle as well as with the phase functions derived for the empirically corrected M³ data. This approach led to the derivation of a photometric correction for maria regions. Finally, it is expected that the proposed correction would be applicable to all HySI images covering the lunar mare region.

     

Searching the Sinus Amoris: Using profiles of geological units,impact and volcanic features to characterize a major terrane interface on the Moon

Geochemical profiles of surface units, impact, and volcanic features are studied in detail to determine the underlying structure in an area of extensive mare/highland interface, Sinus Amoris. This study region includes and surrounds the northeastern embayment of Mare Tranquillitatis. The concentrations of two major rock-forming elements (Mg and Al), which were derived from the Apollo 15 orbital geochemical measurements, were used in this study. Mapped units and deposits associated with craters in the northwestern part of the region tend to have correlated low Mg and Al concentrations, indicating the presence of KREEP-enriched basalt. Found along the northeastern rim of Tranquillitatis were areas with correlated high Mg and Al concentration, indicating the presence of troctolite. Distinctive west/east and north/south trends were observed in the concentrations of Mg and Al, and, by implication, in the distribution of major rock components on the surface. Evidence for a systematic geochemical transition in highland or basin-forming units may be observed here in the form of distinctive differences in chemistry in otherwise similar units in the western and eastern portions of the study region.     

Reflectance spectra of analog basalts; implications for remote sensing of lunar geology

Lunar mare basalts, highland anorthosites and KREEP are the three major lunar rock types reported from the lunar surface. In the present study, we interpret the reflectance spectral behavior of lunar analog basalts including massive basalt, vesicular basalt and amygdaloidal basalt collected from the Deccan basaltic region, which are considered as equivalent of lunar mare basalts. Reflectance spectra of analog basalts were measured at three different environments: in the field, under controlled field conditions and in the lab. In field conditions the reflectance spectra were measured under 350-1050 nm spectral range. During controlled field and lab condition, reflectance spectra were measured under 350-2500 nm range covering the UV, visible, NIR, and SWIR regions. The spectral characteristics of basalts measured under different environments and their merits and demerits were discussed. However, lab spectra have given clear, reliable diagnostic spectral information for our present objective. The major oxides and minerals of analog basalts were compared with lunar mare basalts. The presence of Ca-pyroxene, ferrous and ferric iron and their diagnostic spectral features in basalts are discussed for study of lunar mare region.     

Reflectance Spectral Characteristics of Lunar Surface Materials

Based on a comprehensive analysis of the mineral composition of major lunar rocks (highland anorthosite, lunar mare basalt and KREEP rock), we investigate the reflectance spectral characteristics of the lunar rock-forming minerals, including feldspar, pyroxene and olivine. The affecting factors, the variation of the intensity of solar radiation with wavelength and the reflectance spectra of the lunar rocks are studied. We also calculate the reflectivity of lunar mare basalt and highland anorthosite at 300 nm, 415 nm, 750 nm, 900 nm, 950 nm and 1000 nm. It is considered that the difference in composition between lunar mare basalt and highland anorthosite is so large that separate analyses are needed in the study of the reflectivity of lunar surface materials in the two regions covered by mare basalt and highland anorthosite, and especially in the region with high Th contents, which may be the KREEP-distributed region.     

Stratigraphy and evolution of basalts in Mare Humorum and southeastern Procellarum

Abstract— We have studied the mare basalts of Mare Humorum and southeastern Procellarum (30°W–50°W, 0°–40°S). One hundred and nine basaltic units have been identified from differences in their FeO wt% and TiO₂ wt% content, and variations in crater densities. Crater counting and reference to isotopically dated Apollo samples have provided an age for 33 major units. Some evidence for three distinct periods of volcanic activity has been found. We found that the large unit in the middle of Mare Humorum is the oldest in the basin. This supports the suggestion that the oldest central unit sank causing the lithosphere to bend and create dykes through which lava flowed to produce the outer units. No evidence of a trend in FeO wt% and TiO₂ wt% content against time is found within Mare Humorum. There appears to be no lateral trend of basalts in terms of FeO and TiO₂ wt% over the entire area with time. An increase in FeO content with time is found in the 33 major units and there is some evidence for an increase in TiO₂ in the same units. A correlation between FeO wt% and TiO₂ wt% content is evident when all 109 units are compared. A notable feature of this correlation is a sharp increase in gradient of TiO₂ wt% content when the FeO wt% content rises above about 17%.     

Mare humorum: An integrated study of spectral reflectivity

A detailed study was made of the spectral reflectivity (0.3–1.1 μm) of 31 areas (10–20 km in diam) in the Humorum basin region. The results are: (1) There are at least two units in the mare portion of Humorum which are distinguishable by spectral properties. One of these units, called T-type, has a spectral reflectivity resembling that of the Apollo 11 site and also some areas in Oceanus Procellarum. The other unit in southwest Mare Humorum, resembles Mare Serenitatis in spectral character (S-type). An additional unit in the central area (I-type) with intermediate spectral properties is possible. (2) These mare units do not correlate with obvious morphological or albedo changes but agree well with shadings distinguishable on color difference photographs. (3) On the basis of studies of previously sampled sites it is suggested that the T-type unit may be higher in Ti content (similar to Apollo 11) than the S-type material (similar to Apollo 12). (4) The continuity of T-type material through the break in the northeast wall of Mare Humorum and its spectral similarity to areas in Procellarum suggest that the T-type material may result from an event that flooded parts of Mare Procellarum at a period later than the original Humorum basin filling (S-type). Relative ages derived from crater morphology studies support this sequence.     

Minerals mapping of the lunar surface with Clementine UVVIS/NIR data based on spectra unmixing method and Hapke model

The distribution of minerals on the lunar surface is information which could contribute to studying lunar origin and evolution. In this paper, the distribution of clinopyroxene, orthopyroxene, olivine, ilmenite, and plagioclase on the lunar surface has been mapped based on Hapke radiative transfer model and linear unmixing of spectra with Clementine UVVIS/NIR data. The results have been validated on the basis of minerals modal abundance data of the Apollo samples, and problems in the minerals abundance mapping have been analyzed. The validation based on analysis data of Apollo samples indicates that plagioclase mapped in this paper represents the total abundance of plagioclase and agglutinitic glass. The minerals mapping results show that the lunar surface is mainly composed of pyroxene, plagioclase, agglutinitic glass, and ilmenite. Basalt in the lunar mare is mainly composed of clinopyroxene and ilmenite, and lunar highland is mainly composed of plagioclase and agglutinitic glass. Orthopyroxene is mainly distributed on the north of Mare Imbrium, on the south of Maria and Aitken Basin. According to our results, there is probably no large area of olivine distribution on the lunar surface which is different from earlier published results. Therefore, emphasis should be put on the olivine distribution in the minerals mapping using hyperspectral data such as M³ of Chandrayaan-1 and IIM of ChangE-1.     

Integration and Comparison of Clementine and Lunar Prospector Data: Global Scale Multielement Analysis1 (Fe,Ti, and Th) of the Lunar Surface

In this paper, we present (1) a statistical analysis, based on a systematic clustering method, of a dataset integrating the global abundance maps of the three elements iron, titanium, and thorium derived from Clementine and Lunar Prospector and (2) a comparison of iron abundances between Clementine and Lunar Prospector. Homogeneous geologic units are compositionally characterized and spatially defined in relation to the major rock types sampled on the Moon. With the lowest abundances of Fe, Ti, and Th found on the Moon, the lunar highland terrains are quite homogeneous with two major large feldspathic units, one being slightly more mafic than the other. Two distinct regions with unique compositions are unambiguously identified: the Procellarum KREEP Terrane (PKT) and the South Pole–Aitken (SPA). The PKT, which includes all the units with Th abundances higher than 3.5 ppm (KREEP-rich materials), is delimited by an almost continuous ringlike unit. In particular, it includes the western nearside maria, except for Mare Humorum. With concentrations in Fe, Ti, and Th enhanced relative to the surrounding highlands, the South Pole–Aitken basin floor represents a large mafic anomaly on the far side, suggesting wide deposits of lower crust and possible mantle materials. However, due to indirect residual latitude effects in the CSR (Clementine spectral reflectance) measurements, iron abundances might have been overestimated in SPA, thus implying that crustal materials, rather than mantle materials, might represent the dominant contributor to the mafic component exposed on the basin floor.     

Stratigraphy,evolution, and volume of basalts in Mare Serenitatis

Abstract– Fourteen major basaltic units in Mare Serenitatis have been identified and mapped from differences in TiO₂ wt%. The ages of these units have been inferred from their crater densities and reference to isotopically dated Apollo samples. It has been found that FeO and TiO₂ wt% of the units do not show any apparent trend with time. However, the oldest units have much greater variation in FeO and TiO₂ wt% than younger ones. No lateral trend in the age of the basaltic units is apparent within the basin. A vertical profile of Mare Serenitatis has been produced based on the depth of basalt within impact craters. The minimum depth of basalt has been estimated where craters have not exposed underlying highland material. The profile has been used to estimate the minimum volume of basalt within the basin to be ≈500,000 km³.     

Searching for high alumina mare basalts using Clementine UVVIS and Lunar Prospector GRS data: Mare Fecunditatis and Mare Imbrium

In the context of sample evidence alone, the high-alumina (HA) basalts appear to be an unique, and rare variety of mare basalt. In addition to their distinct chemistry, radiometric dating reveals these basalts to be among the oldest sampled mare basalts. Yet, HA basalts were sampled by four missions spanning a lateral range of ∼2400 km, with ages demonstrating that aluminous volcanism lasted at least 1 billion years. This evidence suggests that HA basalts may be a widespread phenomenon on the Moon. Knowing the distribution of HA mare basalts on the lunar surface has significance for models of the origin and the evolution of the Lunar Magma Ocean. Surface exposures of HA basalts can be detected with compositional remote sensing data from Lunar Prospector Gamma Ray Spectrometer and Clementine. We searched the lunar surface for regions of interest (ROIs) that correspond to the intersection of three compositional constraints taken from values of sampled HA basalts: 12-18 wt% FeO, 1.5-5 wt% TiO₂, and 0-4 ppm Th. We then determined the “true” (unobscured by regolith) composition of basalt units by analyzing the rims and proximal ejecta of small impacts (0.4-4 km in diameter) into the mare surface of these ROIs. This paper focuses on two ROIs that are the best candidates for sources of sampled HA basalts: Mare Fecunditatis, the landing site of Luna 16; and northern Mare Imbrium, hypothesized origin of the Apollo 14 HA basalts. We demonstrate our technique's ability for delineating discrete basalt units and determining which is the best compositional match to the HA basalts sampled by each mission. We identified two units in Mare Fecunditatis that spectrally resemble HA basalts, although only one unit (Iltm) is consistent with the compositional and relative age of the Luna 16 HA samples. Northern Mare Imbrium also reveals two units that are within the compositional constraints of HA basalts, with one (Iltm) best matching the composition of the basalts sampled by Apollo 14.     

A correlation study based on Al/Si x-ray fluorescence data from Southwestern part of mare serenitatis

The Tacquet Formation in southwestern Mare Serenitatis has unusually low visible albedos for the Al/Si intensity ratios measured by the Apollo 15 X-ray fluorescence experiment. This is a contradiction of the demonstrated good correlation between Al/Si and visible albedo data. To understand why this situation exists, a correlation study has been undertaken. This study is based on Al/Si intensity ratios and includes such other remote sensing data as visible and near IR spectral reflectance, color-difference and color-ratio photography, and broad spectrum visible albedo measurements. The Tacquet unit appears to have: (1) an average Al/Si intensity which is intermediate between mare and highland values (=0.21); (2) visible albedos equivalent to the two darkest mare units in the Tranquillitatis-Serenitatis area; (3) a low titanium content; and (4) a relatively high glass-to-crystal ratio. The evidence indicates that the discrepancy between visible albedos and Al/Si intensities in the vicinity of the Tacquet Formation might be due primarily to the addition of highland-type ejecta from the crater, Menelaus, onto a low albedo mare unit. The possibility that the formation consists of dark, high Al material such as spinel, perhaps extruded from the Menelaus Rilles, cannot be excluded, although no such material has been sampled by the lunar missions.     

The D-CIXS X-ray spectrometer on the SMART-1 mission to the Moon—First results

The SMART-1 mission has recently arrived at the Moon. Its payload includes D-CIXS, a compact X-ray spectrometer. SMART-1 is a technology evaluation mission, and D-CIXS is the first of a new generation of planetary X-ray spectrometers. Novel technologies enable new capabilities for measuring the fluorescent yield of a planetary surface or atmosphere which is illuminated by solar X-rays. During the extended SMART-1 cruise phase, observations of the Earth showed strong argon emission, providing a good source for calibration and demonstrating the potential of the technique. At the Moon, our initial observations over Mare Crisium show a first unambiguous remote sensing of calcium in the lunar regolith. Data obtained are broadly consistent with current understanding of mare and highland composition. Ground truth is provided by the returned Luna 20 and 24 sample sets.     

The magnetic characteristics of returned lunar samples and 5heir implications for regolith processes

Magnetic observations yield information about the amount and nature of the magnetic phases present in a sample. They reveal that the predominant magnetic phase in the lunar samples is metallic iron which is sometimes alloyed with nickel and cobalt. In the mare basalts less than 0.1% of metallic iron is present, whereas in the non-mare crystalline rocks several percent of iron has been found in some samples. The soils have approximately 0.5% of iron, which is fine grain, rather pure iron occurring in impact glass. In the recrystallized breccias and the igneous rocks the iron is coarser. Systematic minor variations in metallic iron content in the soils reveal soil maturity trends. Mixing between highland and mare soils can be traced with the Fe²⁺ content. Mare soils differ from highland soils in having a higher value of reduced remanence. The magnetic characteristics of the Apollo 14 breccias are not consistent with the progressive metamorphism of a common starting material. Shock welding in the range of tens of kbs can account for the characteristics of some of the ‘unmetamorphosed’ breccias. Greater shock accompanied by recovery can account for the magnetic characteristics of the ‘recrystallized’ breccias.     

Mare serenitatis: a preliminary definition of surface units by remote observations

There are many surface units in Mare Serenitatis and in the adjacent Montes Haemus that can be defined by remote, Earth-based observations at visual, infrared, and radar wavelengths. These highland and mare surface units are obvious in color-difference photographs and in radar images, while the infrared images have little or no differences. These characteristics are consistent with units having definite chemical differences. However, a better definition of these surfaces requires the synthesis of many more data sets.Paper presented at the Lunar Science Institute Conference on Geophysical and Geochemical Exploration of the Moon and Planets, January 10–12, 1973.This paper presents the results of one phase of research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under Contract No. NAS 7–100, sponsored by the National Aeronautics and Space Administration.     

Compositional and temporal investigation of exposed lunar basalts in the Mare Imbrium region

This paper presents an updated stratigraphical and compositional study of the exposed maria within the Imbrium basin on the Moon. Clementine multispectral data were employed to derive TiO₂ and FeO wt% abundance estimates of potentially distinct basaltic flows. Additionally, NASA Lunar Orbiter images were used to estimate flow ages using crater count statistics. Mare Imbrium shows evidence of a complex suite of low to high-Ti basaltic lava units infilling the basin over an 800 million year timescale. More than a third (37%) of identified mare basalts were found to contain 1-3 wt% TiO₂. Two other major mare lithological units (representing about 25% of the surface each) show TiO₂ values between 3-5 and 7-9 wt%. The dominant fraction (55%) of the sampled maria contain FeO between 16 and 18 wt%, followed by 27% of maria having 18-20 wt% and the remaining 18%, 14-16 wt% FeO. A crater frequency count (for diameters >500 m) shows that in three quarters of the sampled mare crater counts range between 3.5 and 5.5×¹⁰⁻² per km², which translates, according to a lunar cratering model chronology, into estimated emplacement ages between ∼3.3 and 2.5 Ga. A compositional convergence trend between the variations of iron and titanium oxides was identified, in particular for materials with TiO₂ and FeO content broadly above 5 and 17 wt%, respectively, suggesting a related petrogenesis and evolution. According to these findings, three major periods of mare infill are exposed in the Imbrium basin; despite each period showing a range of basaltic compositions (classified according to their TiO₂ content), it is apparent that, at least within these local geological settings, the igneous petrogenesis generally evolved through time towards more TiO₂- and FeO-rich melts.     

Report of the Working Party on the classification of the lunar igneous rocks

Abstract— A report is presented for a possible revised classification of lunar igneous rocks that still uses the division of Moon rocks into mare and highland types. It subdivides the mare rocks into basalts depending on TiO₂ content and glasses depending on colour, and subdivides the highland rocks principally into KREEP basalts and into coarse‐grained igneous rocks comparable to and using terrestrial igneous rock terminology.     

Low crater frequencies and low model ages in lunar maria: Recent endogenic activity or degradation effects?

Recently a number of studies have identified small lunar geologic structures to be <100 Ma in age using standard remote sensing techniques. Here we present new crater size frequency distributions (CSFDs) and model ages using craters D > 10 m for five small target units: one irregular mare patch (IMP) in Mare Nubium and four regions located on lunar wrinkle ridges in Mare Humorum. For comparison we also date another IMP found in a recent study in Mare Tranquillitatis (Braden et al. 2014 ). Absolute model age (AMA) derivation corresponds to 46 ± 5 Ma and 22 ± 1 Ma for Nubium and Sosigenes IMP, respectively. We show that for IMPs and in nearby control mare regions, similar production-like cumulative log–log SFD slopes of −3 are observed. In contrast, control mare regions in Mare Humorum exhibit shallower equilibrium slopes from −1.83 to −2. Three out of four wrinkle ridges appear to be in equilibrium but with crater lifetimes lower than on the corresponding maria. Low crater frequencies on one wrinkle ridge result in an age of 8.6 ± 1 Ma. This study region contains 80% fresh craters, which suggests that the crater population is still in production indicative of a recent resurfacing event.