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  • 1980-1984  (16)
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  • 1
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    The bulk-Moon MgO/FeO ratio: A highlands perspective (1984)
    In:  Other Sources
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    Publikationsdatum: 2019-01-25
    Beschreibung: Compositional data for nonmare (highlands) samples suggest that the Moon's mg ratio (MgO/FeO) is higher than general estimates. Geochemically representative highlands soils have mg ratios of 0.66 (Apollo 16), 0.69 (Luna 20) and 0.73 (ALHA81005). These soils are mixtures of unrelated pristine nonmare rocks, of which there are at least three groups: Mg-rich rocks, ferroan anorthosites, and KREEP. Other than Mg-rich rocks, virtually all pristine rocks have mg 0.65. Thus, assuming the mixing process that sampled Mg-rich materials was random, the average mg of Mg-rich parent magmas was probably at least 0.70. More direct evidence can be derived from the Mg-rich rocks themselves. Nine of them have bulk-rock mg 0.87. Two (15445 A and 67435 PST) contain Fo(92) olivine. Production of melts that crystallized Fo(92) olivine implies that the mg ratios of source regions in lunar mantle were commensurably high. A quantification of this constraint is developed assuming that the parent melts formed by equilibrium (batch) partial melting. Implications of the model are discussed.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Lunar Planetary Inst. Conf. on the Origin of the Moon; p 19
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  • 2
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    Megaregolith thickness, heat flow, and the bulk composition of the Moon (1984)
    In:  Other Sources
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    Publikationsdatum: 2019-01-25
    Beschreibung: Models developed to assess the effects of megaregolith on lunar thermal evolution are discussed. It is confirmed that the two sites where lunar heat flow was measured are probably unrepresentative, with heat flows about 25% higher than regional averages, due to focussing of heat flow towards regions with thin megaregolith. Numerous lines of evidence indicate that the megaregolith is generally 2 to 3 km thick under highlands (which cover about 83% of the total lunar surface), and 1 km thick under maria. In most models, megaregolith thickness is assumed to be roughly 6x greater over highlands than over maria. Based on sparse data for porosity among lunar rock types, and the correlation between thermal conductivity and porosity, it is assumed that megaregolith conductivity is roughly 20 kiloerg s(-1)cm(-1)K(-1), and bedrock conductivity is roughly 7x greater. It is also found that insulation by megaregolith exacerbates the problem of reconciling modest temperatures inferred for the (present) matle with a high rate of heat production; an upper limit of 30 ng/g for the bulk-Moon U content can be derived from this constraint alone.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Lunar Planetary Inst. Conf. on the Origin of the Moon; p 18
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  • 3
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    The origin of the Moon (1984)
    In:  Other Sources
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    Publikationsdatum: 2019-01-25
    Beschreibung: Bulk density alone shows that the Moon is depleted in metallic FeNi relative to the Earth or to chondritic meteorites. This depletion implies that the Moon formed not from chondrites but from differentiated material. Origin of the Moon by fission from the Earth offers a simple explanation for its depletion in FeNi, but this mechanism seems unlikely because of associated dynamical difficulties. Lunar volatile element depletions were invoked in support of fission, but volatile contents of eucritic meteorites are similarly low and the eucrites did not form by Earth fission. A more plausible origin of the Moon is accretion from the circumterrestrial swarm. The low FeNi content of the Moon is understood if the mean size of interplanetary silicate particles was much smaller than that for metal particles, since this would have led to preferential capture of silicates into Earth orbit, but the question arises whether the mean particle size of the metallic particles was great enough to prevent their capture into the swarm.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Lunar Planetary Inst. Conf. on the Origin of the Moon; p 57
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  • 4
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    Petrology and chemistry of two 'large' granite clasts from the moon (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Pristine granite clasts in Apollo-14 breccias 14321 and 14303 have estimated masses of 1.8 and 0.17 g, respectively. The 14321 clast is about 60 percent K-feldspar and 40 percent quartz, with traces of extremely Mg-poor mafic silicates and ilmenite. The 14303 clast is roughly 33 percent plagioclase, 32 percent K-feldspar, 23 percent quartz, 11 percent pyroxene, and 1 percent ilmenite; pyroxene and ilmenite are moderately Mg-rich; plagioclase and pyroxene are strongly zoned. Both clasts are severely brecciated, but monomict (pristine). Both have abundant graphic integrowths of K-feldspar with quartz. Unlike the majority of similar earth rocks, both clasts are devoid of hydrous phases. The bulk composition of the 14321 clast is similar to those of several other lunar granitic samples, but the 14303 clast is unique: it bears as close a resemblance to KREEP as it does to other lunar granites. Silicate liquid immiscibility may explain why the granites are low in REE relative to KREEP.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Earth and Planetary Science Letters (ISSN 0012-821X); 64; 2 Au; Aug. 198
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  • 5
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    Seventh Foray - Whitlockite-rich lithologies, a diopside-bearing troctolitic anorthosite, ferroan anorthosites, and KREEP (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Seventeen nonmare samples, most of them pristine, are characterized, and implications of the new data are discussed. Five pristine samples are from Apollo 14, near the center of the KREEP-rich zone in the moon's western hemisphere. Three of them are alkali anorthosites rich in Ca-phosphate (whitlockite), which apparently crystallized from magmas with REE contents roughly 6 x those of high-K KREEP. The alkali anorthosites probably formed from Mg-rich magmas that assimilated large amounts of urKREEP, but some might have formed by metasomatism of ferroan anorthosite by urKREEP. The gabbronorite/norite classification scheme is not well suited to western hemisphere lithologies, probably due mainly to the overriding effects of longitude-petrochemistry correlations. A diopside-bearing Mg-rich lithology indicates that a low degree of melting was not a prerequisite for producing gabbroic (high-Ca pyroxene-rich) Mg-rich magmas, and suggests that some source regions of Mg-rich magmas were relatively Ca-rich. Several pristine KREEP fragments from Apollo 15 station 2 are texturally and compositionally much like other pristine KREEP, and thus reinforce the evidence that KREEP is highly uniform. The pristine anorthosites, on the other hand, demonstrate further that lunar anorthosites are diverse.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research, Supplement (ISSN 0148-0227); 88; B151-B16
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  • 6
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    Contribution of the mantle to the lunar asymmetry (1980)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Evidence of three kinds indicates a lunar compositional asymmetry: mare basalts are much more abundant on the near side; the incompatible rich KREEP component is mainly observed in near-side soils; and materials on the far side are less dense than those of the near side, as indicated by the 2-km offset between the center of mass and center of figure. Recent models to explain the 2-km offset are based on near side-far side differences in the thickness of crustal units. The most widely discussed model calls for a thickness of anorthosite of about 24 km greater on the far side than on the near side, but no satisfactory method of generating such a large difference has been proposed. It is suggested that much of the offset reflects longitudinal differences in mantle composition, primarily resulting from earlier (or more rapid) crystallization of the magma ocean on what is not the far-side hemisphere. As a result, the far-side mantle would be more magnesian and thus less dense than the near-side mantle.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus; 44; Dec. 198
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  • 7
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    Al-Sm-Eu-Sr systematics of eucrites and moon rocks Implications for planetary bulk compositions (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Constraints are placed on the bulk compositions of the eucrite parent body (EPB) and the moon through analysis of the Eu and Sr 'anomalies' of eucrites and lunar rooks. It is noted that the elements Al, REE, and Sr are incompatible with the major minerals of these small, low-f(O2) bodies,except for plagioclase. Predictions can be derived about the concentrations of Al, REE, and Sr in samples affected by plagioclase fractionation, based on the hypothesis that these elements in the EPB and moon are all in proportions close to those in the bulk solar system. It is determined that the predictions are almost idealy fulfilled by eucrites and lunar samples. For the EPB, the ratios REE/Al, Sr/Al, and Sr/REE are found to be constrained probably within 10 percent of the chondritic ratios. For the moon, the constraints are found to be less precise: REE/Al is very probably within 25 percent of chondritic; Sr/Al and Sr/REE are probably within 35 percent of chondritic; Sr/Al and Sr/REE are probably within 35 percent of chondritic. It is concluded that there is a very strong similarity between the bulk compositions of the planets and the compositions of chondritic meteorites.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 47; Sept
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  • 8
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    Compositional implications regarding the lunar origin of the ALHA 81005 meteorite (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Geochemically, ALHA 81005 has all the attributes expected of a regolith sample from the lunar highlands. Most important is its Fe/Mn ratio (77), within an uncertainty the same as the mean lunar ratio. There are significant differences, however, in comparison to previously sampled lunar regoliths. The closest precedents are the Apollo-16 and Luna-20 regoliths, particularly the latter, but ALHA 81005 has lower contents of Na, Ti, and incompatible elements. Feldspathic granulitic breccias such as 72559, which texturally resemble the most abundant type of clast in ALHA 81005, are also similar compositionally. From its low KREEP and Na contents ALHA 81005 is inferred to have originated well away from the K, Th, and U-rich region near the center of the nearside, at least as far away as the eastern limb.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Geophysical Research Letters (ISSN 0094-8276); 10; Sept
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  • 9
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    Regolith breccia Allan Hills A81005 - Evidence of lunar origin, and petrography of pristine and nonpristine clasts (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: It is shown that the ratios of MnO/FeO in pyroxene, texture (abundant brown and swirly glass, which are typical of lunar regolith breccias) and overall composition (approximately 75 percent plagioclase) indicate a lunar origin for the regolith breccia Allan Hills A81005, presumably from an unsampled region of the moon. The rock is found to differ in detail from other regolith samples; for example, it has exceptionally low contents of Na and KREEP. In addition, a pristine clast is found to contain exceptionally coarse augite in comparison with similar Apollo samples. It is found that ALHA81005 is not perceptibly more shocked than typical Apollo regolith breccias. It is concluded that the discovery of this rock on earth strengthens the suggestion that SNC achondrites were derived by impact ejection from Mars.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Geophysical Research Letters (ISSN 0094-8276); 10; Sept
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  • 10
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    Pristine rocks (8th Foray) - 'Plagiophile' element ratios, crustal genesis, and the bulk composition of the moon (1984)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Eu/Al, Sr/Al, Eu/Sr, and similar ratios among pristine lunar nonmare lithologies with implications for nonmare petrogenesis and for the bulk composition of the moon are examined. On a plot of Eu/Al versus mg, ferroan anorthosites are separated from all other pristine nonmare rocks by a considerable gap. A nonrandom process must be invoked to account for the gap in the spectrum of ratios. A single magma probably cannot account for even the Mg-rich pristine rocks subset, based on diversity of plagiophile ratios among samples with similar mg ratios. Plagiophile ratios also constrain the bulk composition of the moon. Plagiophile ratios among ferroan anorthosites exactly match those expected under a model in which ferroan anorthosites formed by flotation of plagioclase cumulates over a primordial 'magmasphere'. Ratios among nonvolatile elements confirm that the moon formed out of materials akin to chondritic meteorites.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research, Supplement (ISSN 0148-0227); 89; C16-C24
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