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  • 1
    Publication Date: 2019-06-28
    Description: We identify the lithologic and compositional components of soil 76503 based on INAA of 243 2-4-mm particles and 72 thin sections from these and associated 1-2-mm particles (76502). We present a statistical distribution of the major compositional types as the first step of a detailed comparative study of the North and South Massifs. The soil sample was collected well away from any boulder and is more representative of typical North Massif material than any single large rock or boulder sample. So far, our examination of the 76503 particles has provided a better definition of precursor igneous lithologies and their petrogenetic relationships. It has enabled us to refine the nature of mixing components for the North Massif less than 1-mm fines. It has confirmed the differences in lithologies and their proportions between materials of the North and South Massifs; e.g., the North Massif is distinguished by the absence of a 72275-type KREEP component, the abundance of a highly magnesian igneous component, and the absence of certain types of melt compositions found in the South Massif samples.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar Science Inst., Workshop on Geology of the Apollo 17 Landing Site; p 2-4
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  • 2
    Publication Date: 2019-06-28
    Description: Studies of Apollo 17 highland igneous rocks and clasts in breccias from the North and South Massifs have described magnesian troctolite, norite, anorthositic gabbro, dunite, spinel cataclasites, and granulitic lithologies that may have noritic anothosite or anorthositic norite/gabbro as igneous precursors, and have speculated on possible petrogenetic relationships among these rock types. Mineral compositions and relative proportions of plagioclase and plagioclase-olivine particles in samples 76503 indicate that the precursor lithology of those particles were troctolitic anorthosite, not troctolite. Mineral and chemical compositions of more pyroxene-rich, magnesian breccias and granulites in 76503 indicate that their precursor lithology was anorthositic norite/gabbro. The combination of mineral compositions and whole-rock trace-element compositional trends supports a genetic relationship among these two groups as would result from differentiation of a single pluton. Although highland igneous lithologies in Apollo 17 materials have been described previously, the proportions of different igneous lithologies present in the massifs, their frequency of association, and how they are related are not well known. We consider the proportions of, and associations among, the igneous lithologies found in a North Massif soil, which may represent those of the North Massif or a major part of it.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar Science Inst., Workshop on Geology of the Apollo 17 Landing Site; p 24-26
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  • 3
    Publication Date: 2019-06-28
    Description: Among the highland lithologies of 2-4 mm rock fragments in North Massif soil 76503, we have found a compositional group, low in incompatible element concentrations, that we interpret as representing the pre-Serenitatis surface. A component of these materials is an igneous-textured lithology that we believe formed in large impact melts. These are compositionally similar to, and possibly precursors of, many of the granulitic breccias that appear to be mixtures of ferroan and magnesian-suite rocks. The polymict, or old, upper-crustal breccias, along with granulitic breccias and the endogenous igneous lithologies found particularly at the North Massif stations, constitute the poorly consolidated portions of North Massif. Highland samples from the South Massif, on the other hand, are enriched in materials of the competent, impact-melt breccias formed by the Serenitatis impact. The competent melt-breccias contain clasts of most of the pre-existing surface materials, but they also contain components not found in the rocks of the poorly consolidated massif materials.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Twenty-Fourth Lunar and Planetary Science Conference. Part 2: G-M; p 727-728
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  • 4
    Publication Date: 2019-06-28
    Description: A phosphate-rich clast in a pigeonite-plagioclase mineral assemblage occurs in Apollo 17 impact-melt breccia 76503,7025. The clast, measuring 0.9 x 0.4 mm in thin section, contains 3.3 percent (volume) apatite (Ca5P3O12(F,Cl)), 0.8 percent whitlockite (Ca16(Mg,Fe)2REE2P14O56), and trace monazite ((LREE)PO4). Major minerals include 26 percent pigeonite, En53-57FS34-35W08-13, and 69 percent plagioclase, An84-92Ab7-15Oro.6-1.1. Troilite, ilmenite, and other accessory minerals constitute less than 1 percent of the assemblage and Fe-metal occurs along fractures. Also present in the melt breccia as a separate clast is a fragment of felsite. Based on the association of these clasts and their assemblages, a parent lithology of alkali-anorthositic monzogabbro is postulated. Monazite occurs in the phosphate-bearing clast as two less than 10 micron grains intergrown with whitlockite. The concentration of combined REE oxides in monazite is 63.5 percent and the chondrite-normalized REE pattern is strongly enriched in LREE, similar to lunar monazite in 10047,68 and terrestrial monazite. Thorium concentration was not measured in monazite, but based on oxide analyses of approximately 100 percent (including interpolated values for REE not measured), substantial Th concentration is not indicated, similar to monazite in 10047,68. Measured monazite/whitlockite REE ratios are La: 11, Ce: 8, Sm: 3.6, Y: 0.9, and Yb: 0.5. Compositions of monazite and coexisting whitlockite and apatite are given.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Twenty-Fourth Lunar and Planetary Science Conference. Part 2: G-M; p 725-726
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  • 5
    Publication Date: 2019-07-13
    Description: Compositions, including REEs determined by ion microprobe, of apatite and whitlockite in lunar rock assemblages rich in incompatible trace elements, are presented. Concentrations of REEs in lunar whitlockites are high, ranging from about 1.2 to 2.1 REEs (lanthanides + Y) per 56 oxygens. This slightly exceeds the level of two REE atoms per 56 oxygens at which the dominant substitution theoretically becomes saturated. This saturation effect leads to whitlockite REE(3+) D values at typical lunar whitlockite REE concentrations which are 30-40 percent lower than the D values at low concentrations. The halogen-to-phosphorous ratio in lunar melts is a key factor determining the REE distribution with crystalline assemblages. As long as P and REE concentrations of melts are in KREEP-like proportions, one or both of the phosphates will saturate in melts at similar REE concentrations.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 57; 16; p. 4069-4094.
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  • 6
    Publication Date: 2019-07-12
    Description: MAC88104 and 88105, paired meteorites of noritic anorthosite composition, are examined. Results indicate that these meteorites contain a variety of materials including impact-melt breccias, igneous and metamorphosed bressia clasts, glass clasts and veins, mineral clasts, and extralunar meteoritic debris. Compositions of the bulk meteorite and its components suggest that it came from a region of the moon's crust that was highly aluminous, low in incompatible trace elements, and ferroan in character.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 55; 3051-307
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