嫦娥一号干涉成像光谱仪数据再校正与全月铁钛元素反演

月球表面的元素和物质成分分布是理解月球成岩与地质演化历史的重要线索。嫦娥一号干涉成像光谱仪(IIM)是我国首台月球探测成像光谱仪器,其获得的大量月球高光谱数据已成为我国未来探测月球成分与地质演化研究的宝贵基础数据。本文利用探月工程地面应用系统发布的IIM B版本2C级数据,开发出一套数据再定标流程,获得了较为可靠的月表相对反射率数据。我们在新校正数据的基础上开展月球表面FeO、TiO_2的反演建模,获得了全月FeO和TiO_2分布图,这些图件是进行月球地质填图的基础。校正数据反演的FeO和TiO_2分布与前人对Clementine UVVIS数据的反演结果相近,表明干涉成像光谱仪数据具有较大的应用潜力。高地的低铁岩石成分(一般小于8%)佐证了月球月壳形成的过程中的岩浆洋分异假说,而月海玄武岩的TiO_2成分变化范围较大(0~13%)则表明月海玄武岩来源于不同的月幔源区。根据嫦娥一号干涉成像光谱仪全月FeO分布图,可将月球表面物质类型总体划分为高地斜长岩和月海玄武岩,而根据TiO_2分布可以进一步将月海玄武岩划分为5种不同钛含量的玄武岩岩石类型。FeO和TiO_2在全月范围内的分布表明Apollo和Luna返回的月球样品不能够代表全月范围内的矿物成分多样性,月球岩浆演化历史比前人认为的要复杂。未来月球样品返回任务(如嫦娥五号)如能赴这些特殊地区进行取样,将很有可能返回重要的月球科学研究发现和成果。     

Feldspathic lunar meteorites and their implications for compositional remote sensing of the lunar surface and the composition of the lunar crust

We present new compositional data for six feldspathic lunar meteorites, two from cold deserts (Yamato 791197 and 82192) and four from hot deserts (Dhofar 025, Northwest Africa 482, and Dar al Gani 262 and 400). The concentrations of FeO (or Al₂O₃) and Th (or any other incompatible element) together provide first-order compositional information about lunar polymict samples (breccias and regoliths) and regions of the lunar surface observed from orbit. Concentrations of both elements on the lunar surface have been determined from data acquired by orbiting spacecraft, although the derived concentrations have large uncertainties and some systematic errors compared to sample data. Within the uncertainties and errors in the concentrations derived from orbital data, the distribution of FeO and Th concentrations among lunar meteorites, which represent ∼18 source regions on the lunar surface, is consistent with that of 18 random samples from the surface. Approximately 11 of the lunar meteorites are low-FeO and low-Th breccias, consistent with large regions of the lunar surface, particularly the northern farside highlands. Almost all regoliths from Apollo sites, on the other hand, have larger concentrations of both elements because they contain Fe-rich volcanic lithologies from the nearside maria and Th-rich lithologies from the high-Th anomaly in the northwestern nearside. The feldspathic lunar meteorites thus offer our best estimate of the composition of the surface of the feldspathic highlands, and we provide such an estimate based on the eight most well-characterized feldspathic lunar meteorites. The variable but high (on average) Mg/Fe ratio of the feldspathic lunar meteorites compared to ferroan anorthosites confirms a hypothesis that much of the plagioclase at the surface of the feldspathic highlands is associated with high-Mg/Fe feldspathic rocks such as magnesian granulitic breccia, not ferroan anorthosite. Geochemically, the high-Mg/Fe breccias appear to be unrelated to the mafic magnesian-suite rocks of the Apollo collection. Models for the formation of the upper lunar crust as a simple flotation cumulate composed mainly of ferroan anorthosite do not account for the complexity of the crust as inferred from the feldspathic lunar meteorites.     

The Luna 20 lithic fragments,and the composition and origin of the lunar highlands

Luna 20 soil 22003,1 (250–500 μ) is similar to Apollo 16 soil 61501,47 (250–500 μ) in terms of the percentage of different types of particles. However, among the lithic fragments, the Apollo 16 sample contains a greater percentage of fragments with more than 70 wt. % modal plagioclase and a significantly greater proportion of KREEP-rich particles. Modal analyses of non-mare lithic fragments in Luna 20 and Apollo 11, 14, 15 and 16 indicate that the KREEP-poor highland regions (the bulk of the lunar terrae), though relatively feldspathic, are compositionally inhomogeneous, ranging in plagioclase content from approximately 35 to 100 wt. %. The average plagioclase content lies in the range 45–70 wt.%. Luna 20 pyroxene analyses cluster in two groups, one more magnesian than the other. The groups persist when pyroxene analyses from KREEP-poor noritic, troctolitic and anorthositic lithic fragments from Apollo 11, 14, 15 and 16 and Luna 20 are included. Olivine compositions mimic these pyroxene groups.Within each pyroxene group Cr₂O₃ and TiO₂ decrease as $\text{Fe}\text{(Fe + Mg)}$ increases, suggesting a relationship by fractional crystallization. The two groups suggest that at least two magma compositions were involved. To account for these observations we envisage a Moon-wide magma system in which initial accretionary heterogeneities were imperfectly erased by diffusion and convection. During the cooling of this magma system fractional crystallization was effected by the flotation of plagioclase and sinking of pyroxene, olivine and perhaps ilmenite. The endproduct was an upper layer enriched in plagioclase and a lower layer enriched in mafic silicates. KREEP-rich rocks, which are predominantly noritic in major element composition, may be mechanical mixtures of KREEP-poor norite and material residual after fractional crystallization of the surface magma system.     

Lunar geochemistry as told by lunar meteorites

About 36 lunar meteorites have been found in cold and hot deserts since the first one was found in 1979 in Antarctica. All are random samples ejected from unknown locations on the Moon by meteoroid impacts. Lithologically and compositionally there are three extreme types: (1) brecciated anorthosites with high Al₂O₃ (26–31%), low FeO (3–6%), and low incompatible elements (e.g., <1 μg/g Th), (2) basalts and brecciated basalts with high FeO (18–22%), moderately low Al₂O₃ (8–10%) and incompatible elements (0.4–2.1 μg/g Th), and (3) an impact-melt breccia of noritic composition (16% Al₂O₃, 11% FeO) with very high concentrations of incompatible elements (33 μg/g Th), a lithology that is identified as KREEP on the basis of its similarity to Apollo samples of that designation. Several meteorites are polymict breccias of intermediate composition because they contain both anorthosite and basalt. Despite the large range in compositions, a variety of compositional parameters together distinguish lunar meteorites from terrestrial materials. Compositional and petrographic data for lunar meteorites, when combined with mineralogical and compositional data obtained from orbiting spacecraft in the 1990s, suggest that Apollo samples identified with the magnesian (Mg-rich) suite of nonmare rocks (norite, troctolite, dunite, alkali anorthosite, and KREEP) are all products of a small, geochemically anomalous (noritic, high Th) region of crust known as the Procellarum KREEP Terrane and are not, as generally assumed, indigenous to the vast expanse of typical feldspathic crust known as the Feldspathic Highlands Terrane. Magnesian-suite rocks such as those of the Apollo collection do not occur as clasts in the feldspathic lunar meteorites. The misconception is a consequence of four historical factors: (1) the Moon has long been viewed as simply bimodal in geology, mare or highlands, (2) one of the last, large basin-forming bolides impacted in the Procellarum KREEP Terrane, dispersing Th-rich material, (3) although it was not known at the time, the Apollo missions all landed in or near the anomalous Procellarum KREEP Terrane and collected many Th-rich samples formed therein, and (4) the Apollo samples were interpreted and models for lunar crust formation developed without recognition of the anomaly because global data provided by orbiting missions and lunar meteorites were obtained only years later.     

Major element compositions of Luna 20 glass particles

Major element analyses of nineteen Luna 20 glass particles indicate that most of the Luna 20 glasses have Al₂O₃ contents greater than 21 wt.% and compositions similar to Apollo 10 and Luna 20 rocks and soils. Three of the glass particles have low Al₂O₃ (< 13 wt.%) and high FeO (> 18 wt.%) contents and were probably derived from one of the adjacent maria. The low glass content of the Luna 20 soil indicates that it is relatively young or less mature than most mare soils that have been studied.     

The geochemistry and provenance of Apollo 16 mafic glasses

The regolith of the Apollo 16 lunar landing site is composed mainly of feldspathic lithologies but mafic lithologies are also present. A large proportion of the mafic material occurs as glass. We determined the major element composition of 280 mafic glasses (>10 wt% FeO) from six different Apollo 16 soil samples. A small proportion (5%) of the glasses are of volcanic origin with picritic compositions. Most, however, are of impact origin. Approximately half of the mafic impact glasses are of basaltic composition and half are of noritic composition with high concentrations of incompatible elements. A small fraction have compositions consistent with impact mixtures of mare material and material of the feldspathic highlands. On the basis of major-element chemistry, we identified six mafic glass groups: VLT picritic glass, low-Ti basaltic glass, high-Ti basaltic glass, high-Al basaltic glass, KREEPy glass, and basaltic-andesite glass. These glass groups encompass 60% of the total mafic glasses studied. Trace-element analyses by secondary ion mass spectroscopy for representative examples of each glass group (31 total analyses) support the major-element classifications and groupings. The lack of basaltic glass in Apollo 16 ancient regolith breccias, which provide snapshots of the Apollo 16 soil just after the infall of Imbrium ejecta, leads us to infer that most (if not all) of the basaltic glass was emplaced as ejecta from small- or moderate-sized impacts into the maria surrounding the Apollo 16 site after the Imbrium impact. The high-Ti basaltic glasses likely represent a new type of basalt from Mare Tranquillitatis, whereas the low-Ti and high-Al basaltic glasses possibly represent the composition of the basalts in Mare Nectaris. Both the low-Ti and high-Al basaltic glasses are enriched in light-REEs, which hints at the presence of a KREEP-bearing source region beneath Mare Nectaris. The basaltic andesite glasses have compositions that are siliceous, ferroan, alkali-rich, and moderately titaniferous; they are unlike any previously recognized lunar lithology or glass group. Their likely provenance is within the Procellarum KREEP Terrane, but they are not found within the Apollo 16 ancient regolith breccias and therefore were likely deposited at the Apollo 16 site post-Imbrium. The basaltic-andesite glasses are the most ferroan variety of KREEP yet discovered.     

Feldspathic lunar meteorites Pecora Escarpment 02007 and Dhofar 489: Contamination of the surface of the lunar highlands by post-basin impacts

PCA (Pecora Escarpment) 02007 and Dhofar 489 are both meteorites from the feldspathic highlands of the Moon. PCA 02007 is a feldspathic breccia consisting of lithified regolith from the lunar surface. It has concentrations of both incompatible and siderophile elements that are at the high end of the ranges for feldspathic lunar meteorites. Dhofar 489 is a feldspathic breccia composed mainly of impact-melted material from an unknown depth beneath the regolith. Concentrations of incompatible and siderophile elements are the lowest among brecciated lunar meteorites. Among 19 known feldspathic lunar meteorites, all of which presumably originate from random locations in the highlands, concentrations of incompatible elements like Sm and Th tend to increase with those of siderophile elements like Ir. Feldspathic meteorites with high concentrations of both suites of elements are usually regolith breccias. Iridium derives mainly from micrometeorites that accumulate in the regolith with duration of surface exposure. Micrometeorites have low concentrations of incompatible elements, however, so the correlation must reflect a three-component system. We postulate that the correlation between Sm and Ir occurs because the surface of the Feldspathic Highlands Terrane has become increasingly contaminated with time in Sm-rich material from the Procellarum KREEP Terrane that has been redistributed across the lunar surface by impacts of moderate-sized, post-basin impacts. The most Sm-rich regolith breccias among feldspathic lunar meteorites are about 3× enriched compared to the most Sm-poor breccias, but this level of enrichment requires only a few percent Sm-rich material typical of the Procellarum KREEP Terrane. The meteorite data suggest that nowhere in the feldspathic highlands are the concentrations of K, rare earths, and Th measured by the Lunar Prospector mission at the surface representative of the underlying “bedrock;” all surfaces covered by old regolith (as opposed to fresh ejecta) are at least slightly contaminated. Dhofar 489 is one of 15 paired lunar-meteorite stones from Oman (total mass of meteorite: 1037 g). On the basis of its unusually high Mg/Fe ratio, the meteorite is likely to have originated from northern feldspathic highlands.     

On the origin of impact glass in the Apollo 16 regolith

This study addresses the issue of what fraction of the impact glass in the regolith of a lunar landing site derives from local impacts (those within a few kilometers of the site) as opposed to distant impacts (10 or more kilometers away). Among 10,323 fragments from the 64-210-μm grain-size fraction of three Apollo 16 regolith samples, 14% are impact glasses, that is, fragments consisting wholly or largely of glass produced in a crater-forming impact. Another 16% are agglutinates formed by impacts of micrometeorites into regolith. We analyzed the glass in 1559 fragments for major- and minor-element concentrations by electron probe microanalysis and a subset of 112 of the fragments that are homogeneous impact glasses for trace elements by secondary ion mass spectrometry. Of the impact glasses, 75% are substantially different in composition from either the Apollo 16 regolith or any mixture of rocks of which the regolith is mainly composed. About 40% of the impact glasses are richer in Fe, Mg, and Ti, as well as K, P, and Sm, than are common rocks of the feldspathic highlands. These glasses must originate from craters in maria or the Procellarum KREEP Terrane. Of the feldspathic impact glasses, some are substantially more magnesian (greater MgO/FeO) or have substantially lower concentrations of incompatible elements than the regolith of the Apollo 16 site. Many of these, however, are in the range of feldspathic lunar meteorites, most of which derive from points in the feldspathic highlands distant from the Procellarum KREEP Terrane. These observations indicate that a significant proportion of the impact glass in the Apollo 16 regolith is from craters occurring 100 km or more from the landing site. In contrast, the composition of glass in agglutinates, on average, is similar to the composition of the Apollo 16 regolith, consistent with local origin.     

Antarctic lunar meteorites Yamato-793169, Asuka-881757, MIL 05035, and MET 01210 (YAMM): Launch pairing and possible cryptomare origin

The Antarctic lunar meteorite Meteorite Hills (MET) 01210 is a polymict regolith breccia, dominantly composed of mare basalt components. One relatively large (2.7 × 4.7 mm) basalt clast in MET 01210 (MET basalt) shows remarkable mineralogical similarities to the lunar-meteorite crystalline mare basalts Yamato (Y)-793169, Asuka (A)-881757, and Miller Range (MIL) 05035. All four basalts have similar rock texture, mineral assemblage, mineral composition, pyroxene crystallization trend, and pyroxene exsolution lamellae. The estimated TiO₂ contents (∼2.0 wt%) of the MET basalt and MIL 05035 are close to the bulk-rock TiO₂ contents of Y-793169 and A-881757. These similarities suggest that Y-793169, A-881757, MIL 05035, and the MET basalt came from the same basalt flow, which we designate the YAMM basalt. The source-basalt pairing of the YAMM is also supported by their similar REE abundances, crystallization ages (approx. 3.8-3.9 Ga), and isotopic compositions (low U/Pb, low Rb/Sr, and high Sm/Nd). The pyroxene exsolution lamellae, which are unusually coarse (up to a few microns) by mare standards, imply a relatively slow cooling in an unusually thick lava and/or subsequent annealing within a cryptomare. Reported noble gas and CRE data with close launch ages (∼1 Ma) and ejection depths (deeper than several meters) among the four meteorites further indicate their simultaneous ejection from the moon. Despite the marginally close terrestrial ages, pairing in the conventional Earth-entry sense seems unlikely because of the remote recovery sites among the YAMM meteorites.The high abundance (68%) of mare components in MET 01210 estimated from a two-component mixing model calculation could have resulted from either lateral mixing at a mare-highland boundary or vertical mixing in a cryptomare. The proportion of mare materials in MET 01210 is greater than in Apollo core samples at the mare-highland boundary. The burial depth (>several meters deep) inferred from the lack of surface irradiation of MET 01210 exceeds the typical mare regolith thickness (a few meters). Thus, the source of the YAMM meteorites is likely a terrain of locally high mare-highland mixing within a cryptomare. We searched for a possible source crater of the YAMM meteorites within the well-defined cryptomare, based on the multiple constraints obtained from this study and published data. An unnamed 1.4 km-diameter crater (53°W, 44.5°S) on the floor of the Schickard crater is the most suitable source for the YAMM meteorites.The ²³⁸U/²⁰⁴Pb (μ) value of the YAMM basalts is extremely low, relative to those of the Apollo mare basalts, but comparable to those of the Luna 24 very low-Ti basalts. The low-μ source indicates a derivation from a less differentiated mantle with a lack of KREEP components. Although the chemical sources of materials and heat source of melting might be independent, the heat source that generated the source magma of the YAMM and Luna 24 basalts may not be related to KREEP, unlike the case of the Apollo basalts. The distinct chemical and isotopic compositions of mantle sources between the Apollo basalts and the YAMM/Lunar 24 basalts imply differences in mantle composition and thermal evolution between the Procellarum KREEP Terrane (PKT) and non-PKT regions of the nearside.     

月球表面多种金属元素的分布特征初探

美国的"克莱门汀"(Clementine)和"月球探测者"(Lunar Prospector)号月球探测器,分别于1994和1998年完成了对月球形貌、水冰以及月球重力和磁场等物理参数的高精度、高分辨率探测。月球探测者号还利用伽马射线仪探测了月表层中铁、钛、铀、钍和钾等元素含量分布,这为进一步研究月球的空间与表面环境,月球的地形、地貌、地层与地质构造,月表土壤与岩石的分布、成分与成因,月球物理场特征,月球的内部结构、演化与成因提供了大量的科学数据和证据。根据"克莱门汀"和"月球探测者"号测得的数据,对月球表面金属钛、铁、镁、铀、钍、钾的分布进行分析,初步研究了这些金属元素分布与月球地貌的关系,计算各金属元素之间空间分布的相关系数,分析蕴藏这些金属资源地区的岩性及各种元素可能的来源。由此推测30亿年前月球内部逐渐固化,大量小行星对月表岩石频繁的撞击导致金属元素分布不均衡,使金属元素在月球高原地带普遍含量低于月海,同时也形成了现在我们看到的遍布月表的环形山。     

A lunar differentiation model in light of new chemical data on Luna 20 and Apollo 16 soils

Fines from a Luna 20 soil sample and from three Apollo 16 deep drill core samples have been analyzed for major-minor element abundances by a combined, semi-micro atomic absorption spectrophotometric and colorimetric method. Both the major element and large ion lithophile trace element abundances in these soils, the first from interior highland sites, are greatly influenced by the very high normative plagioclase content, being distinctly richer in Al and Ca, and poorer in K, P, Cr, Mn, Fe, and Ti, than most bulk soil samples from previous lunar missions. The relatively large compositional variations in the Apollo 16 core can be ascribed almost entirely to decreasing plagioclase with increasing depth. The chemical composition of the Luna 20 soil indicates less plagioclase and less KREEP than in the Apollo 16 soils. A lunar differentiation model is presented in which is made the suggestion that KREEP is the result of a second fusion event in a lunar crust consisting of early feldspathic cumulates and primary aluminous ‘liquid’.     

Inversion of the Main Mineral Compositions and Subdivision of Tectonic Units on Lunar LQ-4 based on Chang’e Data

Spectra are sensitive in detecting main minerals on the lunar surface from visible light to infrared light. Since spectral characteristics of minerals are closely related to their compositions and the maturity level of soil on the Moon, studying the compositions and distribution of elements and minerals on the lunar surface can help to understand the evolution of the Moon through remote sensing technology. The correlation between the spectral characteristics of Chang’e-1 interference imaging spectrometry (IIM) reflectance images and the mineral contents of LSCC (Lunar Soil Characterization Consortium) lunar surface mineral samples was discussed and the spatial distributions of FeO and Al2O3 contained in both pyroxene and plagioclase on LQ-4 were studied using the improved angle parameter method, MNF, and band ratio statistics. A comparison of the mapping results of the optical models by Lucey, Shkuractov and other researchers on Clementine and the gamma ray spectrometry data shows that the content error is within 0.6% for lunar mare areas and close to 1% for the highland areas. The tectonic framework on the lunar surface was also investigated. And based on integrated analysis of previous findings on topography of the lunar surface, Chang’e LAM, CCD and LOLA images and the gravity anomalies data (Clementine GLGM-2), the tectonic unit subdivision was established for LQ-4, the idea of subdividing the lunar tectonic units was proposed, and this will provide a good foundation for studying the lunar tectonic evolution.     

Chemical composition of Luna 20 rocks and soil and Apollo 16 soils

The abundances of 24 major, minor and trace elements have been measured by INAA in Luna 20 metaigneous rocks 22006,1 and 22007,1, breccia 22004 and soil 22001,9 and in Apollo 16 soils 62281, 66041 and 66081. An additional 12 trace meteoritic and non-meteoritic elements have also been determined in 22001 and 62281 soils by RNAA. The bulk compositions of L 20 and Ap 16 rocks and soils show close similarity between the two highland sites. There are appreciable differences in bulk compositions between the L 20 highland and the L 16 mare site (120 km apart), suggesting little intermixing of rocks and soils from either site. Luna 20 rocks 22006 and 22007 are nearly identical in chemical composition to Ap 16 metaigneous rocks 61156 and 66095. Luna 20 rocks are feldspathic and are similar to low K-type Fra Mauro basalts. Such rocks and anorthositic gabbros appear to be the major components in highland soils. Luna 20 soil can be distinguished from Ap 16 soils by lower abundances of Al₂O₃, CaO and large ion lithophilic elements. Luna 20 breccia 22004 probably is compacted soil. All L 20 samples show negative Eu anomalies with $\text{Sm}\text{Eu}$ ratios of 5.8, 7.2, 3.9 and 3.3 for rocks 22006, 22007, breccia 22004 and soil 22001, respectively. Norite-KREEP is insignificant, ≤1 per cent, at the L 20 highland site. The derivation of the L 20 soil may be explained by ≈33 per cent of L 20 metaigneous rocks and ≈ 65 per cent anorthositic gabbroic breccia rocks like 15418 (with a positive Eu anomaly) and ≈ 2 per cent meteoritic contributions. Interelement correlations observed previously for maria are also found in highland samples. Luna 20 and Ap 16 soils are low in alkalis. Both soils show an apparent Cd-Zn rich component similar to that observed at the mare sites and high 11 abundances relative to mare sites. The Ap 16 (62281) soil contains a fractionated meteoritic component (probably ancient) of ≈ 1.5 per cent in addition to ≈ 1.9 per cent Cl like material. Luna 20 soil may simply contain 1.9 per cent Cl equivalent.     

The mineralogy and petrology of the Luna 20 soil sample

Fragments of igneous rocks, glasses and minerals comprise 25 per cent of the studied sample of the Luna 20 soil. Basalt fragments in the Luna 20 soil are similar to basalts from the mare regions of the Moon—in that they are characterized by the presence of iron-rich olivines and pyroxenes. On the basis of the FeO contents of plagioclases, it appears possible to distinguish between the plagioclase of the mare and highland regions of the Moon. Other igneous rock fragments are anorthosite, gabbroic anorthosite and anorthositic gabbro. The most abundant rock type (75 per cent of the sample) is microbreceia. One third of the fragments of microbreccia have undergone thermal metamorphism resulting in the homogenization of phases and the development of poikioblastic and hornfelsic textures. Excluding the basalt fragments, the dominant minerals in the Luna 20 soil are anorthite (An_93–98), magnesium-rich orthopyroxenes, intermediate clinopyroxenes and olivine (< Fa₅₀). Chemically, the Luna 20 and Apollo 16 soil samples are similar, but the Luna 20 soil is slightly depleted in aluminum and calcium and enriched in iron and magnesium relative to the Apollo 16 soils. The slight difference in bulk chemistry of the two soils may be a result of the presence of a minor amount of mare material in the Luna 20 soil and its apparent absence in the Apollo 16 soils.     

Composition of the Descartes region,lunar highlands

Analytical data for 40 elements are reported for Apollo 16 soils 60601, 61181, 61501, 64801, 67701, 68501, 65701 and breccias 60015, 60017, 60018, 60315, 61016, 61175, 65015 and 66055. The soils are uniform except for the North Ray Crater rim sample which is richer in Al₂O₃.The breccia components show great diversity in composition. Low-K Fra Mauro basalt, Highland basalt (anorthositic gabbro) and plagioclase are important constituents. Medium-K Fra Mauro basalt is an important constituent of breccias 65015 and 60315.The breccias contain many meteorite fragments and high nickel contents, evidence of the early highland bombardment.Most of the refractory elements (REE, Th, U, Zr, Hf, Nb, Ba) show strong positive correlations, interpreted as resulting from mixing. The REE patterns of the breccias show extreme variation relative to chondrites. There is a good inverse correlation between REE and the europium anomaly ($\text{Eu}\text{Eu}{}^{\mathrm{x}}$). The $\text{La}\text{Yb}$ ratio is constant at 3.1 except in plagioclase. Eu depletion or enrichment is interpreted as due to addition or removal of plagioclase.The Cayley and Descartes formations cannot be distinguished chemically and the differences in surface expression are not due to chemical distinctions. They are interpreted as structural differences, related to early highland cratering and mare basin formation.The complex soil and breccia compositions are related to mixing of four components. These are Low-K Fra Mauro basalt, Highland basalt (anorthositic gabbro) and subordinate plagioclase and Medium-K Fra Mauro basalt. These compositions have been used in a computer program (PETMIX III) to provide fits for the analytical data in terms of the end-members.An average highland composition is proposed, based on the Apollo 15 and 16 orbital data for Si, Al, Mg and Th. Abundances for most other elements are derived from the interelement relationships and correlations, and checked by the mixing program.The resulting composition consists of 69 per cent Highland basalt (anorthositic gabbro) and 31 per cent Low-K Fra Mauro basalt. There is no significant Eu anomaly. The abundances are: SiO₂: 45.2 per cent; TiO₂: 0.68 per cent; Al₂O₃: 24.9 per cent; FeO: 6.3 per cent; MgO: 8.5 per cent; CaO: 13.8 per cent; Na₂O: 0.4 per cent; K₂O: 0.11 per cent; Cr₂O₃: 0.11 per cent; Ba: 144 ppm; Th: 1.8 ppm; U: 0.46 ppm; Pb: 1.6 ppm; Zr: 156 ppm; Hf: 3.2 ppm; Nb: 10.8 ppm; Y: 32 ppm; ΣREE: 85 ppm.     

Feldspathic Mare Basalts at the Apollo 17 Landing Site, Taurus-Littrow

The basalt target rocks that have been converted to regolithacross the lunar maria are everywhere more feldspathic and lessmafic than the basalt hand specimens recovered from four Apollolanding sites, an effect not due to either horizontal or verticalmixing with adjacent highland materials. These crushed targetrocks need to be characterized by direct chemical and petrographicanalysis of the lithic fragments of basalt in the regolithsand by determination of the phase equilibria in and adjacentto these compositions at low pressure. Such data are availablefor the basalts of Mare Crisium and Mare Nubium (Luna 16, 24)and for Very Low Titanium basalt, first defined by three lithicfragments from the Apollo 17 core. These are all feldspathicbasalts, as are those from the Mare Tranquillitatis and OceanusProcellarum soils (Apollo 11, 12). Such data are lacking forthe principal basalt components at Mare Imbrium and Mare Serenitatis(Apollo 15, 17). The thoroughly investigated Apollo 17 landingsite at Taurus–Littrow, SE Mare Serenitatis, providesan example where other published information may be used toarrive at estimates of the composition of the feldspathic marebasalt that was the principal target material for regolith formation.This crushed basalt composition is that of a liquid close tobeing in simultaneous equilibrium with all of olivine, plagioclase,calcium-rich pyroxene, spinel, armalcolite and ilmenite at lowpressure. The simplest explanation would be that the basaltthat dominated the formation of the regolith comes from a differentflow unit than the hand specimens, but it strains credulitythat not a single hand specimen can be positively assigned tothat upper unit, and not a single soil sample can be positivelyidentified as having formed principally from the unit that providesthe hand specimens. KEY WORDS: cotectic; lithic fragment; lunar; target rock; regolith     

月球水冰探测进展

月球上是否存在水冰是第二次月球探测热潮中的热点问题。 1 994年克莱门汀号 (Clementine)环月探测器搭载的频率为 2 .2 73GHz双基地雷达探测到月球南极一些地区出现同向极化增加等独特的回波特征 ,这些地区正好处于极地永久阴影区 ,表明这些地区可能存在水冰。Arecibo天文台频率为 2 .38GHz的地基雷达对月球极地进行制图 ,也得到类似结论。 1 998年月球勘探者号 (LunarProspec tor)环月探测器搭载的中子探测仪在月球极地永久阴影区探测到高含量的氢信号大多认为是水冰引起的。但雷达探测和中子探测结果均存在多解性。月球表面粗糙度同样可以引起雷达回波呈现出类似水冰的异常特征 ,而中子探测仪测量到的仅仅是氢信号而非水 ,而且月球勘探者号撞击月表之后并没有探测到任何的水蒸气信号。月球极地水冰存在与否、存在形式和存在数量等科学问题的回答需要对月球极地特别是永久阴影区作进一步探索     

基于辐射传输模型的月表铁镁质矿物定量反演:以嫦娥三号着陆区为例

我国嫦娥三号着陆于雨海北部的年轻玄武岩熔岩平原上,该区域的物质成分和矿物组成对于理解月球年轻的火山活动具有重要研究价值。月球全球勘探者(Lunar Prospector,LP)探测的元素数据揭示着陆区附近岩石类型主要为高铁中钛玄武岩(19.5%FeO;5.2%TiO_2)。本研究利用月球矿物绘图仪(Moon Mineralogy Mapper,M~3)获取的嫦娥三号着陆区附近的新鲜撞击坑高光谱数据,采用Hapke辐射传输模型和修正高斯模型(MGM)联合分析,对其年轻月海玄武岩铁镁质矿物进行了定量反演。研究表明该区域玄武岩中矿物组成以单斜辉石矿物为主,存在较高比例的橄榄石。基于光谱库匹配方法和MGM优化分析,我们反演出单斜辉石,斜方辉石,橄榄石和钛铁矿四种矿物的相对体积比为57.6:18.0:15.3:9.1,这一研究结果有待于与嫦娥三号玉兔号月球车上搭栽的红外成像光谱仪数据进行比对,以期从遥感和就位探测两个角度获得对于该地区矿物和岩石类型的全面认识。     

Rare earths,other trace elements and iron in Luna 20 samples

The results of the analysis by neutron activation of six samples from the Luna 20 mission and one sample of < 1 mm fines from Apollo 16 are reported. The concentrations of the rare-earth elements (REE) in the samples of fines from Luna 20 and Apollo 16 are less than those found for corresponding materials from the mare areas but a negative Eu anomaly is still present. The concentrations of the REE in fines from Luna 20 are only about two-thirds as great as in the sample of Apollo 16 fines, but the concentrations of Co, Sc and Cr are greater by factors ranging from 1.5 to 2.3.     

Luna 20 soil: abundance and composition of phases in the 45–125 micron fraction

Glass compositions in the Luna 20 soil indicate a minor contribution of mare rocks and a major contribution of highly feldspathic highland material. Glasses with the composition of Highland basalt (anorthositic gabbro or norite) predominate in a range of highly aluminous glasses.The analyses of minerals in the soil show that the highland rocks have a unique assemblage of minerals that can readily be distinguished from the mineral assemblages of either mare or KREEP basalts. The soils are characterized by abundant anorthitic (An_92–99), low-Fe plagioclase. Highly magnesian orthopyroxenes, pigeonites and augites are the most prominent pyroxenes. Unlike mare basalt pyroxenes, clinopyroxenes with intermediate Ca values are not abundant, but extreme iron enrichment towards pyroxferroite does occur. Olivines are more abundant than at other sites and are Mg-rich, low in Ca and Cr. Spinels with compositions approaching MgAl₂O₄ predominate over pleonastes and chromites. Ilmenite and metal are present but not abundant.These data establish the unique nature of the minerals in the highland soils. The mineral compositions are consistent with derivation from a suite of highly feldspathic rocks in which Highland basalt compositions predominate. Some of the mineral data, particularly from the pyroxenes, are suggestive of surface or near-surface processes, rather than plutonic crystallization.