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A J Irving - One of the best experts on this subject based on the ideXlab platform.
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the density and porosity of Lunar Rocks
Geophysical Research Letters, 2012Co-Authors: Walter S Kiefer, Robert J Macke, D T Britt, A J Irving, Guy J ConsolmagnoAbstract:[1] Accurate Lunar Rock densities are necessary for constructing gravity models of the Moon's crust and lithosphere. Most Apollo-era density measurements have errors of 2–5% or more and few include porosity measurements. We report new density and porosity measurements using the bead method and helium pycnometry for 6 Apollo samples and 7 Lunar meteorites, with typical grain density uncertainties of 10–30 kg m−3 (0.3–0.9%) and porosity uncertainties of 1–3%. Comparison between igneous grain densities and normative mineral densities show that these uncertainties are realistic and that the helium fully penetrates the pore space. Basalt grain densities are a strong function of composition, varying over at least 3270 kg m−3 (high aluminum basalt) to 3460 kg m−3 (high titanium basalt). Feldspathic highland crust has a bulk density of 2200–2600 kg m−3 and porosity of 10–20%. Impact basin ejecta has a bulk density of 2350–2600 kg m−3 and porosity of ∼20%.
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petrogenesis and chronology of Lunar meteorite northwest africa 4472 a kreepy regolith breccia from the moon
Geochimica et Cosmochimica Acta, 2011Co-Authors: K H Joy, I A Crawford, V A Fernandes, R Burgess, Richard Hinton, A T Kearsley, A J IrvingAbstract:Northwest Africa (NWA) 4472 is a polymict Lunar regolith meteorite. The sample is KREEP-rich (high concentrations of potassium, rare earth elements and phosphorus) and comprises a heterogeneous array of lithic and mineral fragments. These clasts and mineral fragments were sourced from a range of Lunar Rock types including the Lunar High Magnesian Suite, the High Alkali Suite, KREEP basalts, mare basalts and a variety of impact crater environments. The KREEP-rich nature of NWA 4472 indicates that the sample was ejected from regolith on the nearside of the Moon in the Procellarum KREEP Terrane and we have used Lunar Prospector gamma-ray remote sensing data to show that the meteorite is most similar to (and most likely sourced from) regoliths adjacent to the Imbrium impact basin. U–Pb and Pb–Pb age dates of NWA 4472 phosphate phases reveal that the breccia has sampled Pre-Nectarian (4.35 Ga) Rocks related to early episodes of KREEP driven magmatism. Some younger phosphate U–Pb and Pb–Pb age dates are likely indicative of impact resetting events at 3.9–4 Ga, consistent with the suggested timing of basin formation on the Moon. Our study also shows that NWA 4472 has sampled impact melts and glass with an alkali-depleted, incompatible trace element-rich (high Sc, low Rb/Th ratios, low K) compositional signature not related to typical Apollo high-K KREEP, or that sampled by KREEPy Lunar meteorite Sayh al Uhaymir (SaU) 169. This provides evidence that there are numerous sources of KREEP-rich protoliths on the Moon.
Paul H. Warren - One of the best experts on this subject based on the ideXlab platform.
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Lunar Rock rain diverse silicate impact vapor condensates in an apollo 14 regolith breccia
Geochimica et Cosmochimica Acta, 2008Co-Authors: Paul H. WarrenAbstract:Abstract Apollo 14 regolith breccia 14076, long known to be uniquely endowed with high-alumina, silica-poor (HASP) material of evaporation-residue origin, has been found to contain a diverse suite of complementary condensates, dubbed GASP (gas-associated spheroidal precipitates). GASP occurs in two forms: as glassy or extremely fine grained quenched-melt spheroids, mostly less than 5 μm across; and as quenched textured clasts up to 200 μm across. In two of the clasts, origin by aggregation of spheroidal GASP is confirmed by the presence of relict spheroids. GASP is distinctively depleted in the same refractory major oxides that are characteristically enriched in HASP: Al 2 O 3 and CaO. Among the larger GASP spheroids, Al 2 O 3 is seldom >1 wt%; among the clasts, excluding two instances of apparent contamination by Na- and K-rich substrate-derived melt, bulk Al 2 O 3 averages 0.3 wt%. Depletion of Al 2 O 3 and CaO is also manifested by pyroxene compositions in some clasts; e.g., in the largest clast, En 82 Wo 0.45 with 0.07 wt% Al 2 O 3 . Although GASP bulk compositions are nearly pure SiO 2 + MgO + FeO, they are nonetheless highly diverse. Spheroid compositions range in mg from 7 to 84 mol%, and in FeO/SiO 2 (weight ratio) from 0.002 to 0.67. Bulk compositions and textures of many GASP spheroids suggest that liquid immiscibility occurred prior to quenching; implying that these materials were, some time after condensation, at temperatures of ∼1680 °C. Textural evidence for immiscibility includes lobate boundaries between silicic and mafic domains, and a general tendency for quenched mafic silicates to be concentrated into a few limited patches rather than evenly dispersed. The parent melt of the largest clast’s pyroxene is inferred to have formed as a partial melt within the parent aggregation of GASP matter, compositionally near the pyroxene + cristobalite + melt eutectic and thus at ∼1500 °C. A few GASP spheroids show possible signs of in-flight collision-coalescence, but aggregation of the much larger clasts probably took place in mushy puddles on the Lunar surface. Little mixing took place between these GASP puddles and the related HASP, probably because GASP condensation did not commence until after an intermediate stage during which, while neither net evaporation nor net condensation took place, expansion of the vapor cloud carried the eventual GASP matter well apart from the HASP. Considering the characteristic length-scale of Lunar regolith mixing, the concentration of both GASP and HASP into this single unique regolith sample (14076) is most consistent with a parent crater size (diameter) of 10–100 km. I speculate that the 14076 regolith may have been unusually situated, almost directly uprange from an unusually oblique large impact. Mercurian analogs of the 14076 impact condensates may have significant implications for remote sensing.
James J Mcgee - One of the best experts on this subject based on the ideXlab platform.
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ion and electron microprobe study of troctolites norite and anorthosites from apollo 14 evidence for urkreep assimilation during petrogenesis of apollo 14 mg suite Rocks
Geochimica et Cosmochimica Acta, 1998Co-Authors: John W Shervais, James J McgeeAbstract:Abstract Most of the Moon’s highland crust formed during the period 4.65–4.45 Ga ago from a vast magma ocean up to 800 km deep (Hess and Parmentier, 1995) . This early Lunar crust comprises Fe-rich anorthosites with calcic plagioclase compositions. Subsequent evolution of the highland crust was dominated by troctolites, anorthosites, and norites of the Mg-suite. This plutonic series is characterized by calcic plagioclase, and mafic minerals with high mg# (=100∗Mg/[Mg + Fe]). These Rocks evidently formed by partial melting of ultramafic Rocks of the Lunar mantle, but their bulk Rock incompatible element characteristics are too enriched to represent such a primitive source. Previous studies have suggested that this enrichment in incompatible trace elements is the result of metasomatism of the crust by fluids rich in REE and P. The products of this suggested metasomatic event are REE-rich phosphates (typically whitlockite) deposited interstitially. Alternatively, the incompatible element-rich nature of these plutonic Rocks may represent a characteristic of their parent magma, acquired prior to crystallization of the plutons. In an effort to distinguish the origin of this important Lunar Rock series, we have analyzed the REE content of primary cumulus phases in ten Mg-suite cumulates using SIMS, along with their major and minor element compositions by electron microprobe analysis. Nine of these samples have high mg#s, consistent with their formation from the most primitive parent melts of the Mg-suite. The data presented here show that Mg-suite troctolites and anorthosites preserve major and trace element characteristics acquired during their formation as igneous cumulate Rocks and that these characteristics can be used to reconstruct related aspects of the parent magma composition. Our data show that primitive cumulates of the Mg-suite crystallized from magmas with REE contents similar to high-K KREEP in both concentration and relative abundance. The highly enriched nature of this parent magma contrasts with its primitive major element characteristics, as pointed out by previous workers. This enigma is best explained by the mixing of residual magma ocean urKREEP melts with ultramagnesian komatiitic partial melts from the deep Lunar interior. The data do not support earlier models that invoke crustal metasomatism to enrich the Mg-suite cumulates after formation, or models which call for a superKREEP parent for the troctolites and anorthosites.
Hisayoshi Yurimoto - One of the best experts on this subject based on the ideXlab platform.
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hydrogen isotope ratios in Lunar Rocks indicate delivery of cometary water to the moon
Nature Geoscience, 2011Co-Authors: James P Greenwood, Lawrence A. Taylor, Shoichi Itoh, Naoya Sakamoto, Hisayoshi YurimotoAbstract:Water has been found in many Lunar Rock samples, but its sources are unknown. Isotopic analyses of Apollo samples of Lunar mare basalts and highlands Rocks suggest that a significant volume of water was delivered to the Moon by comets shortly after its formation by giant impact.
John W Shervais - One of the best experts on this subject based on the ideXlab platform.
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ion and electron microprobe study of troctolites norite and anorthosites from apollo 14 evidence for urkreep assimilation during petrogenesis of apollo 14 mg suite Rocks
Geochimica et Cosmochimica Acta, 1998Co-Authors: John W Shervais, James J McgeeAbstract:Abstract Most of the Moon’s highland crust formed during the period 4.65–4.45 Ga ago from a vast magma ocean up to 800 km deep (Hess and Parmentier, 1995) . This early Lunar crust comprises Fe-rich anorthosites with calcic plagioclase compositions. Subsequent evolution of the highland crust was dominated by troctolites, anorthosites, and norites of the Mg-suite. This plutonic series is characterized by calcic plagioclase, and mafic minerals with high mg# (=100∗Mg/[Mg + Fe]). These Rocks evidently formed by partial melting of ultramafic Rocks of the Lunar mantle, but their bulk Rock incompatible element characteristics are too enriched to represent such a primitive source. Previous studies have suggested that this enrichment in incompatible trace elements is the result of metasomatism of the crust by fluids rich in REE and P. The products of this suggested metasomatic event are REE-rich phosphates (typically whitlockite) deposited interstitially. Alternatively, the incompatible element-rich nature of these plutonic Rocks may represent a characteristic of their parent magma, acquired prior to crystallization of the plutons. In an effort to distinguish the origin of this important Lunar Rock series, we have analyzed the REE content of primary cumulus phases in ten Mg-suite cumulates using SIMS, along with their major and minor element compositions by electron microprobe analysis. Nine of these samples have high mg#s, consistent with their formation from the most primitive parent melts of the Mg-suite. The data presented here show that Mg-suite troctolites and anorthosites preserve major and trace element characteristics acquired during their formation as igneous cumulate Rocks and that these characteristics can be used to reconstruct related aspects of the parent magma composition. Our data show that primitive cumulates of the Mg-suite crystallized from magmas with REE contents similar to high-K KREEP in both concentration and relative abundance. The highly enriched nature of this parent magma contrasts with its primitive major element characteristics, as pointed out by previous workers. This enigma is best explained by the mixing of residual magma ocean urKREEP melts with ultramagnesian komatiitic partial melts from the deep Lunar interior. The data do not support earlier models that invoke crustal metasomatism to enrich the Mg-suite cumulates after formation, or models which call for a superKREEP parent for the troctolites and anorthosites.
