Oxide minerals in lithic fragments from Luna 20 fines

One hundred and seventy-six oxide mineral grains in the Luna 20 samples were analyzed by electron microprobe. Spinel is the most abundant oxide, occurring in troctolite fragments. Next most abundant is ilmenite, which occurs in all rock types except those containing spinel. Chromite also occurs in all rock types except those containing spinel. Minor amounts of ulvöspinel, armalcolite, zirkelite, baddeleyite and an unidentified TiO₂-rich phase were also found.Spinel grains are predominantly spinel-hercynite solid solutions, commonly with very minor chromite. The $\text{Fe}\text{(Fe + Mg)}$ ratio is generally lower than in spinel from Apollo 14 rocks. Chromites in non-mare rocks are similar to those from mare rocks. Ilmenite of mare origin is Mg-poor and Zr-rich compared to non-mare ilmenite; these elements may therefore be useful in determining the origin of ilmenite grains.Phase equilibria considerations suggest that spinel troctolite crystallized from a melt high in alumina; a likely candidate is the high-alumina basalt of Prinzet al. (1973a).Sub-micron wide rods of metallic Fe occur in plagioclase grains and may have formed by sub-solidus reduction processes.     

Petrology of some lithic fragments of alkalic high-alumina basalt composition from Apollo 12 coarse fines

Summary The mineralogy and petrology of three lithic fragments of alkalic highalumina basalt (Kreep) composition from the Apollo 12 coarse fines was studied in detail, using an electron microprobe, in order to gain insight into their crystallization histories. Most rocks of this composition are brecciated and our study indicates that a variety of environments of crystallization can be distinguished for mineral fragments and matrices. Mineral fragments are derived from members of the ANT suite (probably troctolites) in fragments 2 and 5, and the alkalic high-alumina basalt suite in fragment 3. The rocks from which they were derived were coarse-grained, recrystallized and equilibrated, as indicated by major, and especially, minor elements. Minor elements in plagioclase, olivine, pyroxene, and zircon are consistently lower in mineral fragments as compared with matrix minerals. The origin of large zircon fragments is problematic but they are probably from the alkalic high-alumina basalt suite. Mineral fragments may have been derived from plutonic rocks (none have yet been recognized from the alkalic high-alumina basalt suite), but possibly also from breccia fragments which were recrystallized in hot, thick ejecta blankets. The matrix of the lithic fragments is of alkalic high-alumina basalt composition and is either igneous or metamorphic, or both. Hence, lithic fragments 2 and 5 are polymict breccias whereas fragment 3 is a monomict breccia. Matrix glasses in fragments 2 and 3 represent melts fractionated along the orthopyroxeneplagioclase cotectic in the olivine-anorthite-silica pseudoternary system. If these liquids could be separated from the residuum and crystallized they would be, as yet, unrecognized members of the alkalic high-alumina basalt suite. The alkalic high-alumina basalt mixing component of fragment 5 (a polymict breccia) has such a composition and may be derived from such a fractionated rock. A mineral fragment of pyroxene intergrown with ilmenite, approximately parallel to (001), is interpreted as decorated shock lamellae rather than as a deep-seated intergrowth, as found in kimberlites. A glass coating on one side of fragment 3 has SiO₂-rich and feldspathic schlieren and appears to be derived, by impact melting, from a rock of granite composition.

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Petrologie einiger Gesteinsfragmente mit alkalic high-alumina basalt Chemismus aus dem Grobanteil von Apollo 12 Bodenproben

Zusammenfassung Drei Gesteinsfragmente mit alkalic high-alumina basalt (Kreep) Chemismus aus der Grobraktion von Apollo 12 Bodenproben wurden mittels einer Elektronenstrahl-Mikrosonde einer detaillierten Studie unterzogen, um Einblick in ihre Genese zu gewinnen. Der überwiegende Teil von Gesteinen dieser Zusammensetzung ist brekziös und unsere Studie zeigt, daß unterschiedliche Kristallisationsbedingungen für die Mineralfragmente und Matrizes herrschten. Die Mineralfragmente in den Fragmenten 2 und 5 stammen von Gesteinen der ANT- (Anorthositisch-Noritisch-Troctolitischen) Reihe (wahrscheinlich von Troctoliten) und in Fragment 3 von Gesteinen der alkalic high-alumina basalt-Reihe.Die Verteilung der Haupt- und Nebenelemente in den Mineralfragmenten zeigt, daß diese von rekristallisierten und equilibrierten, grobkörnigen Gesteinen stammen. Die Konzentrationen der Nebenelemente sind in allen Mineralfragmenten (Plagioklas, Olivin und Zirkon) deutlich geringer als in den Mineralen der Matrix. Die Herkunft der großen Zirkon-Fragmente ist nicht genau zu klären. Sie stammen jedoch wahrscheinlich von Gesteinen der alkalic high-alumina basalt-Reihe. Alle Mineralfragmente könnten von plutonischen Gesteinen stammen (solche sind von der alkalic highalumina basalt-Reihe zur Zeit noch nicht bekannt), sie könnten ihren Ursprung jedoch auch in prä-existenten Brekzien haben, welche in dichten, heißen Auswurfdecken rekristallisierten. Die Matrix der Gesteinsfragmente hat durchwegs eine alkalic high-alumina basalt Zusammensetzung und ist entweder magmatisch oder metamorph, oder beides. Die Fragmente 2 und 5 sind daher als polymikte und das Fragment 3 als monomikte Brekzie zu bezeichnen.Die Matrixgläser in den fragmenten 2 und 3 repräsentieren Rest-schmelzen, welche entlang der Orthopyroxen-Plagioklas-Kotektik im Olivin-Anorthit-SiO₂-System fraktionierten. Diese Schmelzen würden-könnten sie vom System getrennt werden-bisher noch nicht bekannte Glieder der alkalic high-alumina basalt-Reihe darstellen. Eine derartige Zusammensetzung hat jedoch die Mischkomponente im Fragment 5 (eine polymikte Brekzie), welche von einem auf diesem Wege fraktioniertem Gestein stammen könnte.Ilmenit-Lamellen [subparallel zu (001)] in einem Pyroxenfragment stellen eher dekorierte Schocklamellen als Verwachsungen, wie sie aus Kimberliten bekannt sind, dar. Fragment 3 ist einseitig mit einem schlierigen Glas bedeckt, dessen Schlieren angenähert die Zusammensetzung von Alkalifeldspat und reinem SiO₂ haben. Dieses Glas ist offensichtlich eine Impakt-Schmelze eines Gesteines von granitischer Zusammensetzung.

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Petrology of fine-grained rock fragments and petrologic implications of single crystals from the Luna 20 soil

Only fine-grained rocks are present in the Luna 20 samples, and coarser grained rocks are represented by fragments of single crystals. A petrologic study has been made of 47 fine-grained crystalline rocks, microbreccias, and glassy aggregates. In addition, a total of 33 single crystals of pyroxene, plagioclase, olivine and spinel, in the size range 125 to 500 μ, have been examined using electron microprobe and single crystal X-ray diffraction techniques.The most abundant fine-grained crystalline rocks in the samples we have examined are recrystallized anorthositic norite and anorthositic troctolite. Gabbroic rocks, anorthosite, and KREEP basalt are present but not common. Most of the single crystals of pyroxene and plagioclase could have been derived from coarser grained noritic, troctolitic and anorthositic rocks. However, three of the 14 pyroxene crystals, and 2 of the 5 olivine crystals have $\text{Fe}\text{(Fe + Mg)}$ contents greater than 0.45 and are believed to have been derived from mare basalts or related rocks. Two relatively sodic crystals of plagioclase were found. One is a crystal zoned at least over the range An₈₅ to An₆₃, and the second is a homogeneous crystal of albite (~An₃).     

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.     

Petrology of Luna 20 regolith from the lunar highlands

The Luna 20 regolith sample contains crystalline lithic fragments of mare basalt, the anorthosite-norite-troctolite group, and feldspathio basalt. Discrete mineral fragments and mineral fragments in regolith breccias can generally be assigned, based on chemical criteria, to one or the other of the first two rock types. A complex history is indicated for the regolith fragments involving repeated metamorphism and melting of the highlands due to impact events. The glass fragments and the feldspathic basalts probably are the result of this melting and their composition may be representative of a large portion of the regolith at this site.     

Luna 16 microbreccia lithic fragments: Samples of an early basalt filling of mare fecunditatis

Summary Thirty five microbreccia fragments from Mare Fecunditatis recovered by the Luna 16 unmanned mission were studied inPTS by optical microscopy. Bulk compositions were determined by scanning electron beam analysis, and microbreccia constituents (pyroxene, olivine, plagioclase, spinel-group minerals, glasses) were analyzed with the electron microprobe. Results: Microbreccia fragments have bulk and mineral compositions distinctly different from those of aluminous basalt fragments from the same site: FeO, alkalis and FeO/MgO are lower and Cr₂O₃ is higher in the microbreccia fragments. Furthermore, microbreccia fragments are predominantly olivine-normative, whereas the basalt fragments are predominantly quartz-normative. In addition, in the microbreccia fragments, pyroxene compositions cover the range typical of pyroxenes from Luna 16 basalts but extend to more Mg-rich and Ca-poor compositions. Pyroxferroites found in aluminous basalt fragments were not observed in the microbreccia fragments. Plagioclase populations cluster at ) An₉₅ in the microbreccia fragments as compared to ) An₉₀ in the basalt fragments. Compositions of basaltic glasses from within the microbreccia fragments are similar to those from the soil. Conclusions: We found evidence that at the Luna 16 site, two major basalt types are present. One is represented by the 3.42 b.y. old aluminous basalt fragments, the other by the dominant component in the microbreccia fragments and basaltic glasses. The microbreccia fragments and basaltic glasses represent a here tofore unknown lunar basalt type for which we calculate a flatREE pattern with abundances approximately 10× chondritic, thus making it one of the most primitive basalt types known from the Moon. We suggest that this basalt type formed by a relatively high degree of partial melting of a plagioclase bearing source rock at about 60–100 km depth. We further suggest that this basalt type represents older mare fillings now largely covered by younger flows. These younger flows are represented by the aluminous basalt fragments, a rock type that may have formed from a similar source rock by a relatively low degree of partial melting.

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Luna 16 mikrobrekzien fragmente: proben eines frühen basaltes aus dem mare foecunditatis

Zusammenfassung 35 Mikrobrekzien-Fragmente aus der Bodenprobe von Mar Foecunditatis, die von der unbemannten Sonde Luna 16 aufgesammelt wurde, sind in polierten Dünnschliffen mikroskopisch und mittels Elektronenstrahl-Mikrosonde untersucht worden. Pauschalzusammensetzungen der Mikrobrekzien-Fragmente wurden mittels integrierender Elektronen-Raster-Technik und die zusammensetzungen der Komponenten (Pyroxen, Olivin, Plagioklas, Minerale der Spinell-Gruppe und Gläser) mittels konventioneller Elektronenstrahl-Mikroanalyse bestimmt. Resultate: Die Mikrobrekzien-Fragmente unterscheiden sich in ihrer Pauschalzusammensetzung deutlich von den Aluminiumreichen Basaltfragmenten derselben Bodenprobe: FeO- und Alkaligehalte und das FeO/ MgO-Verhältnis sind niedriger und der Cr₂O₃-Gehalt ist höher in den Mikrobrekzien-Fragmenten. Weiters sind die Mikrobrekzien-Fragmente meist Olivin-normativ, während die Basaltfragmente meist Quarz-normativ sind. Auch die Pyroxenzusammensetzungen in den Mikrobrekzien-Fragmenten unterscheiden sich deutlich von jenen der Basaltfragmente durch einen hohen Anteil an Mg-reichen und Ca-armen Pyroxenen, die in den Basaltfragmenten nicht vorkommen. Weiters konnten Pyroxferroite, die typisch für die Luna 16 Basaltfragmente sind, in den Mikrobrekzien-Fragmenten nicht gefunden werden. Die Plagioklas-Zusammensetzungen in den Mikrobrekzien-Fragmenten zeigen ein ausgeprägtes Häufigkeitsmaximum bei ) An₉₅, wogegen das Maximum der Plagioklase in den Basaltfragmenten bei ) An₉₀ liegt. Die Zusammensetzung der Gläser in den Mikrobrekzien-Fragmenten und in den Bodenproben außerhalb der Fragmente ist identisch. Schlußfolgerungen: Die analytischen Daten zeigen, daß an der Luna 16 Landestelle zwei Basalttypen weit verbreitet sind. Der eine Typ ist durch die 3.42×10⁹ Jahre alten Aluminium-reichen Basaltfragmente vertreten, der andere durch die Hauptkomponente der Mikrobrekzienfragmente und basaltischen Gläser. Letzterer repräsentiert einen bisher nicht bekannten Basalttyp vom Mond, der Olivin- und Plagioklas-reich ist und einen niedrigen Spurenelementgehalt hat. Die errechnete Häufigkeit der Seltenen Erden ist etwa 10× chondritische Häufigkeit und weitesgehend unfraktioniert. Dieser neue Basalttyp scheint somit einer der primitivsten zu sein, den wir bisher vom Monde kennen. Er repräsentiert wahrscheinlich eine Schmelze, die durch einen hohen Grad von partieller Aufschmelzung eines plagioklasführenden Ausgangsgesteins in einer Tiefe von etwa 60–100 km entstand. Dieser Basalttyp stellt wahrscheinlich ältere Füllungen des Mare Foecunditatis dar, welche später durch jüngere Basaltergüsse größtenteils bedeckt wurden. Diese jüngeren Basalte sind durch die Basaltfragmente repräsentiert und sind durch hohe Spurenelementgehalte charakterisiert. Die Zusammensetzung der jüngeren Basalte kann durch eine relativ geringe und jene der älteren (Brekzien-) Basalte durch einen hohen Grad partieller Aufschmelzung eines ähnlichen Ausgangsgesteines erklärt werden.

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Chemical composition of Luna 20 soil and rock fragments

Abundances of 22 elements, including 9 rare earth elements (REE), have been determined by ‘monostandard’ instrumental neutron activation analysis of samples from the Luna 20 soil and in 6 rock fragments, including a crystalline rock of highland origin, a breccia of similar composition, a glass and a feldspar grain. The soil appears to have been contaminated with W and Mo. The REE content of the soil is very low, being close to 2.3 times below the level in the Luna 16 soil. Sampling errors, for most elements, are negligible in the case of analyses performed on one or several tens of mg of soil, but they become significant on crystalline rock fragments in the 1–2 mg range.     

Mineralogy,petrology and chemistry of lithic fragments from Luna 20 fines: origin of the cumulate ANT suite and its relationship to high-alumina and mare basalts

Bulk analyses of 157 lithic fragments of igneous origin and analyses of their constituent minerals (plagioclase, pyroxene, olivine, Mg-Al spinel, chromite, ilmenite, armalcolite, baddeleyite, zirkelite, K-feldspar, interstitial glass high in SiO₂ and K₂O) have been used to characterize the lunar highland rock suites at the Luna 20 site. The predominant suite is composed of ANT (anorthositic-noritic-troctolitic) rocks, as found at previous Apollo and Luna sites. This suite consists of an early cumulate member, spinel troctolite, and later cumulate rocks which are gradational from anorthosite to noritic and troctolitic anorthosite to anorthositic norite and troctolite; anorthositic norite is the most abundant rock type and its composition is close to the average composition for the highland rocks at this site. Spinel troctolite is a distinctive member of this suite and is characterized by the presence of Mg-Al spinel, magnesian olivine (average, Fo₈₃), and plagioclase. High-alumina basalt with low alkali content is another important rock type and melt of this composition may be parental to the cumulate ANT suite. Alkalic high-alumina basalt (KREEP) was not found in our sample, but may be genetically related to the ANT suite in that it may have formed by partial melting of rocks similar to those of the ANT suite. Fractional crystallization of low alkali, high-alumina basalt probably cannot produce alkalic high-alumina basalt because the enrichment in KREEP component is many times greater than the simultaneous change in major element components. Formation of alkalic high-alumina basalt by mechanical mixing of ANT rocks with very KREEP-rich components is not likely because the high-alumina basalt suite falls on a cotectic in the anorthiteolivine-silica system. Mare basalts may also be genetically related in that they may have been derived by remelting of rocks formed from residual liquids of fractional crystallization of parental low-alkali, high-alumina basalt, plus mafic cumulate crystals; the resultant melt would have a negative Eu anomaly and high $\text{Fe}\text{Mg}$ and $\text{pyroxene}\text{plagioclase}$ ratios.     

Petrology of glacial sand: implications for the origin and mechanical durability of lithic fragments

The petrology of first cycle (unmodified) and second cycle (reworked) sand at the termini of eleven valley glaciers eroding coarse- to fine-grained bedrock types is determined in order to evaluate the origin and mechanical durability of lithic sands. First cycle sands are coarse- to medium-grained, poorly sorted, fine-skewed, non-modal lithic sands with an average composition of Q₂₁F₆L₇₃. Grain-size distributions do not vary with composition or source rock types, although sands derived from finer grained source rocks contain more lithic fragments than sands from coarser grained sources. By contrast, second cycle sands are medium-grained, poorly sorted, fine- to coarse-skewed arkosic to lithic sands with an average composition of Q₁₉F₄₀L₄₁, and contain fewer lithic fragments than do first cycle sands. We propose that the origin, mechanical durability and survival potential of lithic fragments are related to the types and abundances of their internal planes of weakness, and the particular stress field of the transporting medium. As a result of abrasion, glacial clasts and lithic fragments are subjected to shear stress so that fractures propagate along intracrystal and intercrystal planes of weakness resulting in a continuous grain-size spectrum of lithic fragments and monomineralic grains irrespective of the type of source rock. Upon subsequent aqueous transport in the proglacial environment lithic fragments are subjected to point-loading during saltation in addition to shear stress. Point-loading produces extensional fractures which preferentially propagate along intercrystal planes of weakness, so the lithic fragments break into smaller monomineralic grains and/or lithic fragments. Lithic fragments of very coarse sand-size are abundant in first cycle sands, thus refuting, at least for glacial sands, the widely held view that grains of this size are deficient in nature. The presence of fewer grains of this size in second cycle sands indicates that very coarse sand-size lithic fragments can survive recycling, but in greatly reduced proportions due to breakage.     

Carbon chemistry of Luna 16 and Luna 20 samples

Luna 16 and Luna 20 samples were analyzed for volatilizable species using vacuum pyrolysis to 1400°C. The major gaseous products evolved (ranging from 10–650 μg/g) were H₂O, CO, CO₂, N₂ and CH₄. Minor components (all < 10 μg/g) included NH₃, HCN, NO, SO₂, H₂S, C₂H₂, C₂H₄, C₂H₆, C₃H₆ and higher hydrocarbons, benzene, toluene, and the polymeric contaminants Teflon^® and silicone oil. The total carbon and nitrogen contents (μg/g) for these sieved samples (< 125 μm) were: Luna 16—C 418, N 134 and Luna 20—C 380, N 80.     

Luna 20: mineralogy and petrology of fragments less than 125 μm size

Two milligrams of less than 125 μm size particles from the Luna 20 soil sample (22001,17) have been examined. The results of the mineral identification and analysis verify earlier assumptions that the nature of the lunar highlands is predominantly anorthositic in composition. The presence of highly magnesian clinopyroxene, orthopyroxene and olivine suggests crystallization of Highland rocks in an ultrabasic environment. No fragments were observed that could be unequivocally assigned to mare basalt types.     

The halogens in Luna 16 and Luna 20 soils

Cl and P₂U₅ do not appear to exhibit the same correlation in soils from the Luna 20 and possibly the Luna 16 sites as they do in samples from the Apollo 11–15 sites. Nevertheless, the coherence between labile Cl and other KREEP-related elements is maintained.     

The age and petrography of two Luna 20 fragments and inferences for widespread lunar metamorphism

Ages were determined by the ⁴⁰Ar-³⁹Ar method on two metaclastic rocks returned from the lunar highlands north of Mare Fecunditatis by the Luna 20 probe. Both samples gave very well-defined argon retention ages of 3.90 ± 0.04 AE which are indistinguishable from each other within a resolution of 0.02 AE. Both fragments, 22006 and 22007, are highly recrystallized polymict breccias; there is no evidence for loss of radiogenic ⁴⁰Ar, and the age almost surely dates the time of recrystallization. The cosmic ray exposure ages of these fragments are similar and high: 900 million years for 22006, 1300 million years for 22007. 22007 also contains substantial trapped argon with a high ${}^{40}\text{Ar}{}^{36}\text{Ar}$ ratio.The Luna 20 results greatly extend the area of the Moon's surface exhibiting a well-defined record of metamorphism at 3.9 AE. So far, lunar history in the interval 4.6?3.9 AE is not preserved in the ages of surface rocks. This obliteration suggests lunar-wide metamorphic conditions occurring or terminating at this time as a result of major impacts.     

U-Th-Pb measurements of Luna 20 soil

The concentrations of uranium, thorium and lead and the lead isotopic composition of Luna 20 soil were determined. The data indicate that the Luna 20 soil is mainly a mixture of highland anorthosites and low-K basalt, but little KREEP basalt. The U-Th-Pb systematics are discussed in comparison with other lunar soils, especially with Apollo 16 soils which were collected from a ‘typical’ highland region. The data fit well in the Apollo 16 soil array on a U-Pb evolution diagram, and they exhibit excess lead relative to uranium. This relationship appears to be a characteristic of highland localities. Considering the previous observations of lunar samples, we infer that lead enrichment in the soil relative to uranium occurred between 3.2 and 3.9 b.y. ago and that the soil was disturbed by ‘third events’ about 2.0 b.y. ago. A lunar evolution model is discussed.     

Radiation damage in Luna 20 soil

Micron-sized soil grains from the Luna 20 mission are the most lightly irradiated we have examined, in contrast to micron-sized grains from the Luna 16 soil, which are the most heavily irradiated. Radiation damage in micron-sized grains is inversely correlated with albedo of the soil. The absence of angular, amorphous grains in Luna 20 supports our previous contention that such grains in Luna 16 were produced by intense radiation damage.     

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.     

Oxygen isotopic composition of the Luna 20 soil

The Luna 20 soil (< 125 μm fraction) has a relatively low δO¹⁸ (5.7%.), compared to other lunar soils (5.8 to 6.3%.). This implies either a low-O¹⁸ source material or an unusually small O¹⁸ enrichment in the processes of soil formation and maturation.     

Compositional and X-ray data for Luna 20 feldspar

Electron-microprobe analyses of 46 feldspar grains from the 125–500 μm Luna 20 soil separate range only from 94.5 to 97.5 An (mol. %). One grain differs significantly—An₈₇. Minor element contents are low: K < 0.15 wt.%; Mg < 0.14 wt.%; Fe < 0.15 wt.%. Singlecrystal X-ray data for two analyzed grains show sharp b and c diffractions characteristic of primitive anorthite. The 46 grains are similar in composition to those in feldspar-rich fragments found in all the Apollo missions.     

Chemistry and surface morphology of soil particles from Luna 20 LRL sample 22003

Six siliceous glass spheres, five siliceous glass-bonded agglutinates and one breccia fragment from Luna 20 LRL sample number 22003 were analyzed by optical microscope, scanning electron microscope, scanning electron microprobe and energy-dispersive techniques. The data suggest that most of the glass spheres were probably derived locally by meteoritic impact processes and that most craters on their surfaces may have occurred from impacts of relatively high velocity particles in the impact-produced debris cloud while the glass sphere was at elevated temperatures. This is suggested by the nature of the craters, the partially buried fragments of plagioclase surrounded by radiating fractures and by the apparent absence of craters on the glass surfaces of the glass-bonded agglutinates. One glass sphere has a surface suggestive of a complex multiple impact origin involving liquid siliceous material and numerous siliceous spherules from 0.1 μm to 1 μm in diameter that may have formed from vaporization and condensation processes possibly in a relatively large scale meteoritic impact event.The surfaces of the siliceous glass spheres have several different types of materials. Concentration of metallic iron spherules on the surfaces of the glass spheres is generally lower than for similar Apollo 11 and 12 glass spheres. This is consistent with reduction processes being of primary importance in the formation of this metallic iron. Surface material composed only of Ca, C and O₂, possibly CaCO₃, is probably derived from carbonaceous chondrites. Splashes of material rich in Ca, Al, Fe, K and Cl occur. The origin of the relatively low temperature chlorine-bearing melt is unknown but it may be related to vaporization and condensation processes, possibly volcanic in nature, or possibly to partial fusion of components of carbonaceous chondrites. Siliceous surface material rich in potassium may represent either fused splash material of granitic composition or material enriched by vaporization and condensation processes.     

Petrology of some Glaucophane Schists and Related Rocks from Taiwan

Detailed laboratory study has been made on pre-Tertiary coarse-grainedglaucophane schist, garnet-epidote amphibolite, and epidoteamphibolite in the eastern slope of the Central Mountain Range,Taiwan. These petrotectonic assemblages are considered to beexotic tectonic blocks emplaced within the feebly metamorphosedin situ graphite and quartzose schists of the Yuli belt. Thinlenses of Mn-rich metamorphosed tuff are intercalated withinthe metabasaltic rocks. Such high MnO (2 wt. per cent) and lowMgO (3–4 wt. per cent) tuffaceous rocks are similar inbulk composition to some volcanic clays collected in deep oceanbasins. They consist of the characteristic assemblage Mn-bearinggarnet (5–7 wt. per cent MnO and 30 volume per cent inthe rock)+muscovite+epidote+hornblende+quartz+ albite+rutile?pyrite. Successive stages of conversion of garnet-epidote amphiboliteto blueschist assemblages were noticed. The most recrystallizedschists display abundant Mn-bearing garnet, zoned amphibole,phengite, zoned epidote, stilpnomelane, chlorite, quartz, minoralbite, magnetite, and sphene. The recrystallization processis nearly isochemical except the glaucophane schists appearto be more oxidized and contain more Na₂O than the relict amphibolites.Intimately associated amphibolites of basaltic composition,in contrast, contain the assemblage hornblende+paragonite+epidote+chlorite+quartz+albite+rutile. Microprobe analyses of the coexisting minerals in glaucophaneschists, garnet-epidote amphibolites and epidote amphibolitesyield the following results: (1) garnets, consisting of almandine,spessartine, and grossular components, are less Mn and Mg-richcompared to those in in situ metabasalts of the Franciscan;(2) rim epidotes of the glaucophane schists are more pistastic(X_Fe=0?27–0?30) than that of the garnet-epidote amphibolite(0?2–0?22) implying higher fO₂ values for the glaucophanization;(3) phengitic micas of the glaucophane schist have less Al₂O₃content (29 wt. per cent) than those of the garnet-epidote amphibolite(32 wt. per cent) whereas micas of epidote amphibolites areparagonites with K/(K+Na) ratio of 0?04; (4) the zoned amphibolesshow glaucophane occurring marginal to cores of calcic amphibole.Sodic amphiboles with Al₂O₃ of 6-? to 10?4 wt. per cent arecrossite-glaucophane whereas all calcic amphiboles analyzedare barroisite-pargasite (Al₂O₃ greater than 10 wt. per cent). The garnet-epidote-rutile bearing glaucophane schist of Taiwanprobably recrystallized at temperatures above 350 ?C (the epidotezone) whereas the lawsonite-sphene glaucophane schists of theFranciscan equilibrated below 350 ?C (the lawsonite zone). TheMn-rich basaltic tuffs and their associated flows appear tohave been metamorphosed at profound depths and at the relativelyhigh temperatures of the epidote amphibolite facies, succeededlater by glaucophane schist facies metamorphism at lower temperatures.