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Spicuzza, MJ, Day JMD, Taylor LA, Valley JW.  2007.  Oxygen isotope constraints on the origin and differentiation of the Moon. Earth and Planetary Science Letters. 253:254-265.   10.1016/j.epsl.2006.10.030   AbstractWebsite

We report new high-precision laser fluorination three-isotope oxygen data for lunar materials. Terrestrial silicates with a range of delta O-18 values (-0.5 to 22.9 parts per thousand) were analyzed to independently determine the slope of the terrestrial fractionation line (TFL; lambda = 0.5259 +/- 0.0008; 95% confidence level). This new TFL determination allows direct comparison of lunar oxygen isotope systematics with those of Earth. Values of Delta O-17 for Apollo 12, 15, and 17 basalts and Luna 24 soil samples average 0.01 parts per thousand and are indistinguishable from the TFL. The delta O-18 values of high- and low-Ti lunar basalts are distinct. Average whole-rock delta O-18 values for low-Ti lunar basalts from the Apollo 12 (5.72 +/- 0.06 parts per thousand) and Apollo 15 landing sites (5.65 +/- 0.12 parts per thousand) are identical within error and are markedly higher than Apollo 17 high-Ti basalts (5.46 +/- 0.11 parts per thousand). Evolved low-Ti LaPaz mare-basalt meteorite delta O-18 values (5.67 +/- 0.05 parts per thousand) are in close agreement with more primitive low-Ti Apollo 12 and 15 mare basalts. Modeling of lunar mare-basalt source composition indicates that the high- and low-Ti mare-basalt mantle reservoirs were in oxygen isotope equilibrium and that variations in delta O-18 do not result from fractional crystallization. Instead, these differences are consistent with mineralogically heterogeneous mantle sources for mare basalts, and with lunar magma ocean differentiation models that result in a thick feldspathic crust, an olivine-pyroxene-rich mantle, and late-stage ilmenite-rich zones that were convectively mixed into deeper portions of the lunar mantle. Higher average delta O-18 (WR) values of low-Ti basalts compared to terrestrial mid ocean ridge basalts (Delta=0.18 parts per thousand) suggest a possible oxygen isotopic difference between the terrestrial and lunar mantles. However, calculations of the delta O-18 of lunar mantle olivine in this study are only 0.05 parts per thousand higher than terrestrial mantle olivine. These observations may have important implications for understanding the formation of the Earth-Moon system. (c) 2006 Elsevier B.V. All rights reserved.

Day, JMD, Taylor LA, Floss C, Patchen AD, Schnare DW, Pearson DG.  2006.  Comparative petrology, geochemistry, and petrogenesis of evolved, low-Ti lunar mare basalt meteorites from the LaPaz Icefield, Antarctica. Geochimica Et Cosmochimica Acta. 70:1581-1600.   10.1016/j.gca.2005.11.015   AbstractWebsite

New data is presented for five evolved, low-Ti lunar mare basalt meteorites from the LaPaz Icefield, Antarctica, LAP 02205, LAP 02224, LAP 02226, LAP 02436, and LAP 03632. These basalts have nearly identical mineralogies, textures, and geochemical compositions, and are therefore considered to be paired. The LaPaz basalts contain olivine (Fo(64-2)) and pyroxene (Fs(32)Wo(8)En(60) to Fs(84-86)Wo(15)En(2-0)) crystals that record extreme chemical fractionation to Fe-enrichment at the rims, and evidence for silicate liquid immiscibility and incompatible element enrichment in the mesostasis. The basalts also contain FeNi metals with unusually high Co and Ni contents, similar to some Apollo 12 basalts, and a single-phase network of melt veins and fusion crusts. The fusion crust has similar chemical characteristics to the whole rock for the LaPaz basalts, whereas the melt veins represent localized melting of the basalt and have an endogenous origin. The crystallization conditions and evolved nature of the LaPaz basalts are consistent with fractionation of olivine and chromite from a parental liquid similar in composition to some olivine-phyric Apollo 12 and Apollo 15 basalts or lunar low-Ti pyroclastic glasses. However, the young reported ages for the LaPaz mare basalts (similar to 2.9 Ga) and their relative incompatible element enrichment compared to Apollo mare basalts and pyroclastic glasses indicate they cannot be directly related. Instead, the LaPaz mare basalts may represent fractionated melts from a magmatic system fed by similar degrees of partial melting of a mantle source similar to that of the low-Ti Apollo mare basalts or pyroclastic glasses, but which possessed greater incompatible element enrichment. Despite textural differences, the LaPaz basalts and mare basalt meteorite NWA 032 have similar ages and compositions and may originate from the same magmatic system on the Moon. (c) 2005 Elsevier Inc. All rights reserved.

Day, JMD, Floss C, Taylor LA, Anand M, Patchen AD.  2006.  Evolved mare basalt magmatism, high Mg/Fe feldspathic crust, chondritic impactors, and the petrogenesis of Antarctic lunar breccia meteorites Meteorite Hills 01210 and Pecora Escarpment 02007. Geochimica Et Cosmochimica Acta. 70:5957-5989.   10.1016/j.gca.2006.05.001   AbstractWebsite

Antarctic lunar meteorites Meteorite Hills 01210 and Pecora Escarpment 02007 are breccias that come from different regolith lithologies on the Moon. MET 01210 is composed predominantly of fractionated low-Ti basaltic material and is classified as an immature, predominantly basaltic glassy matrix regolith breccia. PCA 02007 is a predominantly feldspathic regolith breccia consisting of metamorphosed feldspathic, noritic, troctolitic and noritic-anorthosite clasts, agglutinate and impact-glasses, as well as a number of basaltic clasts with mare and possible non-mare affinities. The basalt clasts in MET 0 12 10 have undergone 'Fenner' trend enrichments in iron and may also have witnessed late-stage crystallization of zircon or a zirconium-rich mineral. Some of the features of MET 0 1210 are similar to other basaltic lunar breccia meteorites (e.g., Northwest Africa 773; Elephant Moraine 87521/96008; Yamato 793274/981031), but it is not paired with them. The presence of metamorphic anorthositic clasts as well as agglutinates indicates a small regolith component. Similarities with previously discovered evolved (e.g., LaPaz Icefield 02205; Northwest Africa 032) and ferroan (e.g., Asuka 881757; Yamato 793169) basaltic lunar meteorites suggest a similar mare source region for MET 01210. Despite lack of evidence for pairing, PCA 02007 shares many features with other feldspathic regolith breccias (e.g., Yamato 791197, Queen Alexandra Range 94281), including a high Mg/Fe whole-rock composition, glass spherules, agglutinate fragments and a diverse clast inventory spanning the range of ferroan anorthosite and high magnesium suite rocks. Some of the basalt fragments in this sample are fractionated and have an igneous origin. However, the majority of the basalt fragments are impact melt clasts. PCA 02007 supports previous studies of feldspathic lunar meteorites that have suggested an aluminous crust for the Moon, with compositions more similar to magnesium granulite breccias than ferroan anorthosites. A 'chondrule-like' fragment found in PCA 02007 and unlike any previously described lunar material is described and tentatively identified as the remnants of a chondritic lunar impactor. This clast is porphyritic with equant olivines that have forsterite-rich cores (Fo(> 98)), extreme normal zonation to more fayalitic rims (Fo(> 44)), and a mineral assemblage with rare earth element abundances distinct from described lunar material and more similar to chondrules found in ordinary or carbonaceous chondrites. Its discovery and description is significant for understanding the composition of lunar impactors. Previously, the main evidence for chondritic lunar impactors was from chondritic relative abundances and near chondritic ratios of highly siderophile elements in lunar impact melt breccias. However, the presence of this clast, along with two other chondritic clasts from Apollo soils 12037 and 15602, provides clues to the identity of ancient meteorite impactors on the Moon. (c) 2006 Elsevier Inc. All rights reserved.

Day, JMD, Taylor LA, Floss C, McSween HY.  2006.  Petrology and chemistry of MIL 03346 and its significance in understanding the petrogenesis of nakhlites on Mars. Meteoritics & Planetary Science. 41:581-606. AbstractWebsite

Antarctic meteorite Miller Range (MIL) 03346 is a nakhlite composed of 79% clinopyroxene, similar to 1% olivine, and 20% vitrophyric intercumulus material. We have performed a petrological and geochemical study of MIL 03346, demonstrating a petrogenetic history similar to previously discovered naklilites. Quantitative textural study of MIL 03346 indicates long (> 1 x 10(1) yr) residence times for the Cumulus augite, whereas the skeletal Fe-Ti oxide, fayalite, and sulfide in the vitrophyric intercumulus matrix suggest rapid cooling, probably as a lava flow. From the relatively high forsterite contents of olivine (up to Fo(43)) compared with other nakhlites and compositions of augite cores (Wo(38-42)En(35-40)Fs(22-28)) and their hedenbergite rims, we suggest that MIL 03346 is part of the same or a similar Martian Cumulate-rich lava flow as other nakhlites. However, MIL 03346 has experienced less equilibration and faster cooling than other nakhlites discovered to date. Calculated trace element concentrations based upon modal abundances of MIL 03346 and its constituent minerals are identical to whole rock trace element abundances. Parental melts for augite have REE patterns that are approximately parallel with whole rock and intercumulus melt using experimentally defined partition coefficients. This parallelism reflects closed-system crystallization for MIL 03346, where the only significant petrogenetic process between formation of augite and eruption and emplacement of the nakhlite flow has been fractional crystallization. A model for the petrogenesis of MIL 03346 and the naklilites (Nakhla, Governador Valadares, Lafayette, Yamato-000593, Northwest Africa (NWA) 817, NWA 998) Would include: 1) partial melting and ascent of melt generated from a long-term LREE depleted mantle Source, 2) crystallization of cumulus augite (+/- olivine, +/- magnetite) in a shallow-level Martian magma chamber, 3) eruption of the crystal-laden naklilite magma onto the surface of Mars, 4) cooling, crystal settling, overgrowth, and partial equilibration to different extents within the flow, 5) secondary alteration through hydrothermal processes, possibly immediately succeeding or during emplacement of the flow. This model might apply to single-or multiple-flow models for the nakhlites. Ultimately, MIL 03346 and the other nakhlites preserve a record of magmatic processes in volcanic rocks oil Mars with analogous petrogenetic histories to pyroxene-rich terrestrial lava flows and to komatiites.

Day, JMD, Hilton DR, Pearson DG, Macpherson CG, Kjarsgaard BA, Janney PE.  2005.  Absence of a high time-integrated He-3/(U+Th) source in the mantle beneath continents. Geology. 33:733-736.   10.1130/g21625.1   AbstractWebsite

Volcanic rocks from ocean island and continental flood basalt provinces can exhibit He-3/He-4 ratios greatly in excess of those of mid-oceanic-ridge basalts (MORB). High He-3/He-4 ratios must indicate derivation from a mantle source with high time-integrated He-3/(U+Th) relative to depleted MORB-source mantle. The location of the high He-3/He-4 mantle reservoir is a poorly resolved but important issue because of the constraints it places upon the structure and convective style of Earth's mantle. It has been proposed that the high He-3/He-4 reservoir resides in the upper mantle, rather than the lower mantle, because Earth should be volatile poor and highly differentiated, with incompatible elements (such as He) concentrated in the upper mantle and crust. This hypothesis can be tested using continental intraplate alkaline volcanics (CIAV) that are generated at or near the boundary between the conducting lithospheric and convecting asthenospheric mantle. Olivine and clinopyroxene phenocrysts from Cretaceous to Miocene CIAV from Canada, South Africa, and Uganda have He-3/He-4 ratios more radiogenic than MORB, strongly arguing against a widespread high He-3/He-4 source in the continental lithosphere or the underlying convecting upper mantle. Combined with a global data set of CIAV and continental lithosphere mantle xenoliths, these results provide no evidence for high He-3/He-4 in any samples known to originate from this environment. Therefore, volcanic rocks with He-3/He-4 greater than MORB He-3/He-4 are likely to sample a mantle source with high time-integrated He-3/(U+Th) that cannot exist within or below the continents. This reservoir is also unlikely to exist within the upper mantle as defined by the He-3/He-4 distribution in MORB.

Macpherson, CG, Hilton DR, Day JMD, Lowry D, Gronvold K.  2005.  High-He-3/He-4, depleted mantle and low-delta O-18, recycled oceanic lithosphere in the source of central Iceland magmatism. Earth and Planetary Science Letters. 233:411-427.   10.1016/j.epsl.2005.02.037   AbstractWebsite

New helium and oxygen isotope data and trace element concentrations are reported for volcanic rocks from central Iceland. Basalts that are depleted in the most incompatible trace elements possess a wide range in He-3/He-4 but most ratios are similar to or higher than those of mid-ocean ridge basalt (MORB:similar to 8R(A)[1] [D.W. Graham, Noble gas geochemistry of mid-ocean ridge and ocean island basalts: characterisation of mantle source reservoirs, in: D.P. Porcelli, C.J. Ballentine, R. Wieler (Eds.), Noble gases in Geochemistry and Cosmochemistry, Rev. Mineral. Geochem., vol. 47, 2002, pp. 247-317]). The low concentrations of helium in these rocks suggest that significant degassing has made them susceptible to contamination by low-He-3/He-4 crust, therefore all measured He-3/He-4 are considered minimum estimates for their sources. Elevated helium isotope ratios in the source of these rocks result from interaction with high-He-3/He-4 mantle. The highest oxygen isotope ratios in the depleted rocks are similar to those in melts from typical depleted upper mantle and the range of delta(18)O values is consistent with variable, limited amounts of contamination by Icelandic crust. Most of the incompatible trace element-enriched rocks possess He-3/He-4 ratios that are similar to or lower than those in MORB. These rocks were erupted close to the postulated centre of the Iceland plume. This observation contradicts models in which high-He-3/He-4 characterises the focus of mantle upwelling. A source with MORB-like He-3/He-4 ratios may also be common to other parts of the North Atlantic Igneous Province. The highest delta(18)O values in the enriched rocks are lower than those in MORB and do not appear to have been affected by interaction with low-delta(18)O Icelandic crust. Recycling of hydrothermally altered oceanic crust that has been subducted into the mantle provides a plausible mechanism for generating an O-18-poor source with the trace element and isotopic characteristics of the enriched lavas. (C) 2005 Elsevier B.V All rights reserved.

Day, JMD, Pearson DG, Nowell GM.  2003.  High precision rhenium and platinum isotope dilution analyses by plasma ionisation multi-collector mass spectrometry. Plasma Source Mass Spectrometry: applications and emerging technologies. ( Holland G, Tanner SD, Eds.)., London: RSC Publishing   10.1039/9781847551689  
Rutter, GP, Pearson DG, Phillip G, Day JMD, Ottley CJ.  2003.  The use of ICP-MS in provenancing stone artefacts: Examples from the southern Levant. Plasma Source Mass Spectrometry: applications and emerging technologies. , London: RSC Publishing   10.1039/9781847551689