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Day, JMD, Neal CR.  2019.  To the Moon: A scientific tribute to Lawrence A. Taylor. Geochimica et Cosmochimica Acta. 266:1-8.   https://doi.org/10.1016/j.gca.2019.08.033   Abstract

Professor Lawrence (Larry) Taylor (September 14, 1938 to September 18, 2017) was a true ‘lunatic’: a term coined to describe one of the early pioneers who served as part of the science teams for the Apollo missions to the Moon. He later advocated for a return to the Moon to both improve our understanding of the formation of our nearest neighbor and to support the further exploration of space. Larry’s larger-than-life personality is matched by his scientific legacy of launching the careers of over 50 post-doctoral scholars and graduate students, present authors included, and authoring a staggering number of peer-reviewed publications (>540 at last count). Lunar science has lost one of its greatest science advocates for returning to the Moon and building a permanent human settlement on its surface. Amongst many of Larry’s memorable sayings, his epitaph should surely be: “To the Moon”. This special issue of Geochimica et Cosmochimica Acta is a tribute to Larry’s scientific achievements. The manuscripts within the volume provide a flavor of the wide range of research in which he was engaged.

Day, JMD, Macpherson CG, Lowry D, Pearson DG.  2012.  Oxygen isotope heterogeneity of the mantle beneath the Canary Islands: a discussion of the paper of Gurenko et al. Contributions to Mineralogy and Petrology. 164:177-183.   10.1007/s00410-012-0755-3   AbstractWebsite

Gurenko et al. (Contrib Mineral Petrol 162:349-363, 2011) report laser-assisted fluorination (LF) and secondary ionization mass spectrometry (SIMS) O-18/O-16 datasets for olivine grains from the Canary Islands of Gran Canaria, Tenerife, La Gomera, La Palma and El Hierro. As with prior studies of oxygen isotopes in Canary Island lavas (e.g. Thirlwall et al. Chem Geol 135:233-262, 1997; Day et al. Geology 37:555-558, 2009, Geochim Cosmochim Acta 74:6565-6589, 2010), these authors find variations in delta O-18(ol) (similar to 4.6-6.0 aEuro degrees) beyond that measured for mantle peridotite olivine (Mattey et al. Earth Planet Sci Lett 128:231-241, 1994) and interpret this variation to reflect contributions from pyroxenite-peridotite mantle sources. Furthermore, Gurenko et al. (Contrib Mineral Petrol 162:349-363, 2011) speculate that delta O-18(ol) values for La Palma olivine grains measured by LF (Day et al. Geology 37:555-558, 2009, Geochim Cosmochim Acta 74:6565-6589, 2010) may be biased to low values due to the presence of altered silicate, possibly serpentine. The range in delta O-18(ol) values for Canary Island lavas are of importance for constraining their origin. Gurenko et al. (Contrib Mineral Petrol 162:349-363, 2011) took a subset (39 SIMS analyses from 13 grains from a single El Hierro lava; EH4) of a more extensive dataset (321 SIMS analyses from 110 grains from 16 Canary Island lavas) to suggest that delta O-18(ol) is weakly correlated (R (2) = 0.291) with the parameter used by Gurenko et al. (Earth Planet Sci Lett 277:514-524, 2009) to describe the estimated weight fraction of pyroxenite-derived melt (Xpx). With this relationship, end-member delta O-18 values for HIMU-peridotite (delta O-18 = 5.3 +/- A 0.3 aEuro degrees) and depleted pyroxenite (delta O-18 = 5.9 +/- A 0.3 aEuro degrees) were defined. Although the model proposed by Gurenko et al. (Contrib Mineral Petrol 162:349-363, 2011) implicates similar pyroxenite-peridotite mantle sources to those proposed by Day et al. (Geology 37:555-558, 2009, Geochim Cosmochim Acta 74:6565-6589, 2010) and Day and Hilton (Earth Planet Sci Lett 305:226-234, 2011), there are significant differences in the predicted delta O-18 values of end member components in the two models. In particular, Day et al. (Geochim Cosmochim Acta 74:6565-6589, 2010) proposed a mantle source for La Palma lavas with low-delta O-18 (< 5 aEuro degrees), rather than higher-delta O-18 (c.f. the HIMU-peridotite composition of Gurenko et al. in Contrib Mineral Petrol 162:349-363, 2011). Here we question the approach of using weakly correlated variations in delta O-18(ol) and the Xpx parameter to define mantle source oxygen isotope compositions, and provide examples of why this approach appears flawed. We also provide reasons why the LF datasets previously published for Canary Island lavas remain robust and discuss why LF and SIMS data may provide complementary information on oxygen isotope variations in ocean island basalts (OIB), despite unresolved small-scale uncertainties associated with both techniques.

Day, JMD, Maria-Benavides J, McCubbin FM, Zeigler RA.  2018.  The potential for metal contamination during Apollo lunar sample curation. Meteoritics and Planetary Science. 53:1283-1291.   https://doi.org/10.1111/maps.13074   Abstract

Curation and preparation of samples for chemical analysis can occasionally lead to significant contamination. This issue is of concern in the study of lunar samples, especially those from the Apollo sample collection, where available masses are finite. Here we present compositional data for stainless steels that have commonly been used in the processing of Apollo lunar samples at NASA Johnson Space Center, including a chisel and a vessel typically used to transfer Apollo samples to principal investigators. The Type 304 stainless steels are Cr-rich, with high concentrations of Mn (4000–18,000 ug g1), Cu (1000–22,900 ug g1), Mo (1030–1120 ug g1), and W (72-193 ug g1). They have elevated highly siderophile element (HSE) concentrations (up to 92 ng g1 Os), 187Os/188Os ranging from 0.1310 to 0.1336, and negligible lithophile element abundances. We find that, while metal contamination is possible, significant (≫0.01% by mass) addition of stainless steel is required to strongly affect the composition of the HSE, W, Mo, Cr, or Cu for most Apollo lunar samples. Nonetheless, careful appraisal on a case-by-case basis should take place to ensure contamination introduced through sample processing during curation is at acceptably low levels. A survey of lunar mare basalts and crustal rocks indicates that metal contamination plays a negligible role in the compositional variability of the HSE and W compositions preserved in these samples. Further work to constrain contamination for other properties of Apollo samples is required (e.g., organics, microbes, water, noble gases, and magnetics), but the effect of metal contamination can be well-constrained for the Apollo lunar collection.

Day, JMD, Walker RJ, Warren JM.  2017.  Os-186-Os-187 and highly siderophile element abundance systematics of the mantle revealed by abyssal peridotites and Os-rich alloys. Geochimica et Cosmochimica Acta. 200:232-254.   10.1016/j.gca.2016.12.013   Abstract

Abyssal peridotites are oceanic mantle fragments that were recently processed through ridges and represent residues of both modern and ancient melting. To constrain the nature and timing of melt depletion processes, and the composition of the mantle, we report high-precision Os isotope data for abyssal peridotites from three ocean basins, as well as for Os-rich alloys, primarily from Mesozoic ophiolites. These data are complemented by whole-rock highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re), trace- and major-element abundances for the abyssal peridotites, which are from the Southwest Indian (SWIR), Central Indian (CIR), Mid-Atlantic (MAR) and Gakkel Ridges. The results reveal a limited role for melt refertilization or secondary alteration processes in modifying abyssal peridotite HSE compositions. The abyssal peridotites examined have experienced variable melt depletion (2% to >16%), which occurred >0.5 Ga ago for some samples. Abyssal peridotites typically exhibit low Pd/Ir and, combined with high-degrees of estimated total melt extraction, imply that they were relatively refractory residues prior to incorporation into their present ridge setting. Recent partial melting processes and mid-ocean ridge basalt (MORB) generation therefore played a limited role in the chemical evolution of their precursor mantle domains. The results confirm that many abyssal peridotites are not simple residues of recent MORB source melting, having a more complex and long-lived depletion history.

Peridotites from the Gakkel Ridge, SWIR, CIR and MAR indicate that the depleted MORB mantle has 186Os/188Os of 0.1198356 ±21 (2SD). The Phanerozoic Os-rich alloys yield an average 186Os/188Os within uncertainty of abyssal peridotites (0.1198361 ±20). Melt depletion trends defined between Os isotopes and melt extraction indices (e.g., Al2O3) allow an estimate of the primitive mantle (PM) composition, using only abyssal peridotites. This yields 187Os/188Os (0.1292 ±25), and 186Os/188Os of 0.1198388 ±29, both of which are within uncertainty of previous primitive mantle estimates. The 186Os/188Os composition of the PM is less radiogenic than for some plume-related lavas, with the latter requiring sources with high long-term time-integrated Pt/Os. Estimates of primitive mantle HSE concentrations using abyssal peridotites define chondritic Pd/Ir, which differs from previous supra-chondritic estimates for Pd/Ir based on peridotites from a range of tectonic settings. By contrast, estimates of PM yield non-chondritic Ru/Ir. The cause of enhanced Ru in the mantle remains enigmatic, but may reflect variable partitioning behaviour of Ru at high pressure and temperature.

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, Tait KT, Udry A, Moynier F, Liu Y, Neal CR.  2018.  Martian magmatism from plume metasomatized mantle. Nature Communications. 9:4799.   10.1038/s41467-018-07191-0   Abstract

Direct analysis of the composition of Mars is possible through delivery of meteorites to Earth. Martian meteorites include ∼165 to 2400 Ma shergottites, originating from depleted to enriched mantle sources, and ∼1340 Ma nakhlites and chassignites, formed by low degree partial melting of a depleted mantle source. To date, no unified model has been proposed to explain the petrogenesis of these distinct rock types, despite their importance for understanding the formation and evolution of Mars. Here we report a coherent geochemical dataset for shergottites, nakhlites and chassignites revealing fundamental differences in sources. Shergottites have lower Nb/Y at a given Zr/Y than nakhlites or chassignites, a relationship nearly identical to terrestrial Hawaiian main shield and rejuvenated volcanism. Nakhlite and chassignite compositions are consistent with melting of hydrated and metasomatized depleted mantle lithosphere, whereas shergottite melts originate from deep mantle sources. Generation of martian magmas can be explained by temporally distinct melting episodes within and below dynamically supported and variably metasomatized lithosphere, by long-lived, static mantle plumes.

Dhaliwal, JK, Day JMD, Moynier F.  2018.  Volatile element loss during planetary magma ocean phases. Icarus. 300:249-260.   10.1016/j.icarus.2017.09.002   Abstract

Moderately volatile elements (MVE) are key tracers of volatile depletion in planetary bodies. Zinc is an especially useful MVE because of its generally elevated abundances in planetary basalts, relative to other MVE, and limited evidence for mass-dependent isotopic fractionation under high-temperature igneous processes. Compared with terrestrial basalts, which have δ66Zn values (per mille deviation of the 66Zn/64Zn ratio from the JMC-Lyon standard) similar to some chondrite meteorites (∼+0.3‰), lunar mare basalts yield a mean δ66Zn value of +1.4 ± 0.5‰ (2 st. dev.). Furthermore, mare basalts have average Zn concentrations ∼50 times lower than in typical terrestrial basaltic rocks. Late-stage lunar magmatic products, including ferroan anorthosite, Mg- and Alkali-suite rocks have even higher δ66Zn values (+3 to +6‰). Differences in Zn abundance and isotopic compositions between lunar and terrestrial rocks have previously been interpreted to reflect evaporative loss of Zn, either during the Earth-Moon formatting Giant Impact, or in a lunar magma ocean (LMO) phase. To explore the mechanisms and processes under which volatile element loss may have occurred during a LMO phase, we developed models of Zn isotopic fractionation that are generally applicable to planetary magma oceans. Our objective was to identify conditions that would yield a δ66Zn signature of ∼ +1.4‰ within the lunar mantle. For the sake of simplicity, we neglect possible Zn isotopic fractionation during the Giant Impact, and assumed a starting composition equal to the composition of the present-day terrestrial mantle, assuming both the Earth and Moon had zinc ‘consanguinity’ following their formation. We developed two models: the first simulates evaporative fractionation of Zn only prior to LMO mixing and crystallization; the second simulates continued evaporative fractionation of Zn that persists until ∼75% LMO crystallization. The first model yields a relatively homogenous bulk solid LMO δ66Zn value, while the second results in a stratification of δ66Zn values within the LMO sequence. Loss and/or isolation mechanisms for volatiles are critical to these models; hydrodynamic escape was not a dominant process, but loss of a nascent lunar atmosphere or separation of condensates into a proto-lunar crust are possible mechanisms by which volatiles could be separated from the lunar interior. The results do not preclude models that suggest a lunar volatile depletion episode related to Giant Impact. Conversely, LMO models for volatile loss do not require loss of volatiles prior to lunar formation. Outgassing during planetary magma ocean phases likely played a profound part in setting the volatile inventories of planets, particularly for low mass bodies that experienced the greatest volatile loss. In turn, our result suggest that the initial compositions of planets that accreted from smaller, highly differentiated planetesimals were likely to be severely volatile depleted.

Dhaliwal, JK, Day JMD, Corder CA, Tait KT, Marti K, Assayag N, Cartigny P, Rumble D, Taylor LA.  2017.  Early metal-silicate differentiation during planetesimal formation revealed by acapulcoite and lodranite meteorites. Geochimica et Cosmochimica Acta. 216:115-140.   10.1016/j.gca.2017.06.042   AbstractWebsite

In order to establish the role and expression of silicate-metal fractionation in early planetesimal bodies, we have conducted a highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundance and 187Re-187Os study of acapulcoite-lodranite meteorites. These data are reported with new petrography, mineral chemistry, bulk-rock major and trace element geochemistry, and oxygen isotopes for Acapulco, Allan Hills (ALHA) 81187, Meteorite Hills (MET) 01195, Northwest Africa (NWA) 2871, NWA 4833, NWA 4875, NWA 7474 and two examples of transitional acapulcoite-lodranites, Elephant Moraine (EET) 84302 and Graves Nunataks (GRA) 95209. These data support previous studies that indicate that these meteorites are linked to the same parent body and exhibit limited degrees (<2–7%) of silicate melt removal. New HSE and osmium isotope data demonstrate broadly chondritic relative and absolute abundances of these elements in acapulcoites, lower absolute abundances in lodranites and elevated (>2 × CI chondrite) HSE abundances in transitional acapulcoite-lodranite meteorites (EET 84302, GRA 95209). All of the meteorites have chondritic Re/Os with measured 187Os/188Os ratios of 0.1271 ± 0.0040 (2 St. Dev.). These geochemical characteristics imply that the precursor material of the acapulcoites and lodranites was broadly chondritic in composition, and were then heated and subject to melting of metal and sulfide in the Fe-Ni-S system. This resulted in metallic melt removal and accumulation to form lodranites and transitional acapulcoite-lodranites. There is considerable variation in the absolute abundances of the HSE, both among samples and between aliquots of the same sample, consistent with both inhomogeneous distribution of HSE-rich metal, and of heterogeneous melting and incomplete mixing of silicate material within the acapulcoite-lodranite parent body. Oxygen isotope data for acapulcoite-lodranites are also consistent with inhomogeneous melting and mixing of accreted components from different nebular sources, and do not form a well-defined mass-dependent fractionation line. Modeling of HSE inter-element fractionation suggests a continuum of melting in the Fe-Ni-S system and partitioning between solid metal and sulfur-bearing mineral melt, where lower S contents in the melt resulted in lower Pt/Os and Pd/Os ratios, as observed in lodranites. The transitional meteorites, EET 84302 and GRA 95209, exhibit the most elevated HSE abundances and do not follow modelled Pt/Os and Pd/Os solid metal-liquid metal partitioning trends. We interpret this to reflect metal melt pooling into domains that were sampled by these meteorites, suggesting that they may originate from deeper within the acapulcoite-lodranite parent body, perhaps close to a pooled metallic ‘core’ region. Petrographic examination of transitional samples reveals the most extensive melting, pooling and networking of metal among the acapulcoite-lodranite meteorites. Overall, our results show that solid metal-liquid metal partitioning in the Fe-Ni-S system in primitive achondrites follows a predictable sequence of limited partial melting and metal melt pooling that can lead to significant HSE inter-element fractionation effects in proto-planetary materials.

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Filiberto, J, Chin E, Day JMD, Franchi IA, Greenwood RC, Gross J, Penniston-Dorland SC, Schwenzer SP, Treiman AH.  2012.  Geochemistry of intermediate olivine-phyric shergottite northwest Africa 6234, with similarities to basaltic shergottite northwest Africa 480 and olivine-phyric shergottite northwest Africa 2990. Meteoritics and Planetary Science. 47(8):1256-1273.   10.1111/j.1945-5100.2012.01382.x   Abstract

The newly found meteorite Northwest Africa 6234 (NWA 6234) is an olivine (ol)-phyric shergottite that is thought, based on texture and mineralogy, to be paired with Martian shergottite meteorites NWA 2990, 5960, and 6710. We report bulk-rock major- and trace-element abundances (including Li), abundances of highly siderophile elements, Re-Os isotope systematics, oxygen isotope ratios, and the lithium isotope ratio for NWA 6234. NWA 6234 is classified as a Martian shergottite, based on its oxygen isotope ratios, bulk composition, and bulk element abundance ratios, Fe/Mn, Al/Ti, and Na/Al. The Li concentration and δ7Li value of NWA 6234 are similar to that of basaltic shergottites Zagami and Shergotty. The rare earth element (REE) pattern for NWA 6234 shows a depletion in the light REE (La-Nd) compared with the heavy REE (Sm-Lu), but not as extreme as the known “depleted” shergottites. Thus, NWA 6234 is suggested to belong to a new category of shergottite that is geochemically “intermediate” in incompatible elements. The only other basaltic or ol-phyric shergottite with a similar “intermediate” character is the basaltic shergottite NWA 480. Rhenium-osmium isotope systematics are consistent with this intermediate character, assuming a crystallization age of 180 Ma. We conclude that NWA 6234 represents an intermediate compositional group between enriched and depleted shergottites and offers new insights into the nature of mantle differentiation and mixing among mantle reservoirs in Mars.

Franz, HB, Kim ST, Farquhar J, Day JMD, Economos RC, McKeegan KD, Schmitt AK, Irving AJ, Hoek J, Dottin J.  2014.  Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars. Nature. 508:364-+.   10.1038/nature13175   AbstractWebsite

The geochemistry of Martian meteorites provides a wealth of information about the solid planet and the surface and atmospheric processes that occurred on Mars. The degree to which Martian magmas may have assimilated crustal material, thus altering the geochemical signatures acquired from their mantle sources, is unclear(1). This issue features prominently in efforts to understand whether the source of light rare-earth elements in enriched shergottites lies in crustal material incorporated into melts(1,2) or in mixing between enriched and depleted mantle reservoirs(3). Sulphur isotope systematics offer insight into some aspects of crustal assimilation. The presence of igneous sulphides in Martian meteorites with sulphur isotope signatures indicative of mass-independent fractionation suggests the assimilation of sulphur both during passage of magmas through the crust of Mars and at sites of emplacement. Here we report isotopic analyses of 40 Martian meteorites that represent more than half of the distinct known Martian meteorites, including 30 shergottites (28 plus 2 pairs, where pairs are separate fragments of a single meteorite), 8 nakhlites (5 plus 3 pairs), Allan Hills 84001 and Chassigny. Our data provide strong evidence that assimilation of sulphur into Martian magmas was a common occurrence throughout much of the planet's history. The signature of mass-independent fractionation observed also indicates that the atmospheric imprint of photochemical processing preserved in Martian meteoritic sulphide and sulphate is distinct from that observed in terrestrial analogues, suggesting fundamental differences between the dominant sulphur chemistry in the atmosphere of Mars and that in the atmosphere of Earth(4).

Furi, E, Hilton DR, Murton BJ, Hemond C, Dyment J, Day JMD.  2011.  Helium isotope variations between Reunion Island and the Central Indian Ridge (17 degrees-21 degrees S): New evidence for ridge-hot spot interaction. Journal of Geophysical Research-Solid Earth. 116   10.1029/2010jb007609   AbstractWebsite

We report new helium abundance and isotope results for submarine basaltic glasses from the Central Indian Ridge (CIR) between the Marie Celeste (16.7 degrees S) and Egeria fracture zones (FZ) (20.6 degrees S); the adjacent Gasitao, Three Magi, and Rodrigues ridges; and for olivine separates from lavas and cumulate xenoliths from the Mascarene Islands (Reunion, Mauritius, and Rodrigues). Helium isotope ratios in basaltic glasses range from 7.1 to 12.2 R(A) (where R(A) = air (3)He/(4)He) and lie between values of Mid-Ocean Ridge Basalt (MORB) (8 +/- 1 R(A)) and samples from Reunion Island (11.5 to 14.1 R(A)). The highest (3)He/(4)He values (up to 12.2 R(A)) are found in glasses recovered off axis from the Three Magi and Gasitao ridges. Along the CIR axis, MORB-like (3)He/(4)He ratios are found near the Egeria FZ, and there is a marked increase to values of similar to 11 R(A) between similar to 19 degrees and 20 degrees S. The lowest (3)He/(4)He values (< 8 R(A)) are found immediately south of the Marie Celeste FZ, where incompatible trace element ratios (e. g., La/Sm) are highest. These low (3)He/(4)He ratios can be explained by closed system radiogenic (4)He ingrowth in either (1) a "fossil" Reunion hot spot mantle component, embedded into the subridge mantle when the CIR migrated over the hot spot at similar to 34 Ma or (2) trace element enriched MORB mantle. In contrast, the high (3)He/(4)He ratios observed on the CIR axis adjacent to the Gasitao Ridge, and along the off-axis volcanic ridges, are consistent with flow of hot spot mantle material from Reunion (similar to 1100 km to the west) toward the CIR.

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Gannoun, A, Burton KW, Day JMD, Harvey J, Schiano P, Parkinson I.  2016.  Highly Siderophile Element and Os Isotope Systematics of Volcanic Rocks at Divergent and Convergent Plate Boundaries and in Intraplate Settings. Reviews in Mineralogy and Geochemistry. 81:651-724.   10.2138/rmg.2016.81.11   Abstract

Terrestrial magmatism is dominated by basaltic compositions. This definition encompasses mid-ocean ridge basalts (MORB), which account for more than eighty percent of Earth’s volcanic products and which are formed at divergent oceanic plate margins, as well as intraplate volcanic rocks such as ocean island basalts (OIB), continental flood basalts (CFB) and continental rift-related basalts, and highly magnesian ultramafic volcanic rocks that dominantly occur in Archean terranes, termed komatiites. All of these broadly basaltic rocks are considered to form by partial melting of the upper mantle, followed by extraction from their source regions and emplacement at the Earth’s surface. For these reasons, basalts can be used to examine the nature and extent of partial melting in the mantle, the compositions of mantle sources, and the interactions between the crust and mantle. Because much of Earth’s mantle is inaccessible, basalts offer some of the best ‘proxies’ for examining mantle composition, mantle convection and crust–mantle interactions. By contrast, at arcs, volcanism is dominated by andesitic rock compositions. While some arcs do have basaltic and picritic magmatism, these magma types are rare in convergent plate margin settings and reflect the complex fractional crystallization and often associated concomitant assimilation processes occurring in arcs. Despite the limited occurrence of high MgO magmas in arc volcanic rocks, magmas from this tectonic setting are also important for elucidating the behavior of the HSE from creation of basaltic compositions at mid-ocean ridges to the subduction of this crust beneath arcs at convergent plate margins.

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Harvey, J, Day JMD.  2016.  Highly siderophile and strongly chalcophile elements in high temperature geochemistry and cosmochemistry. (81):774pp.: Mineralogical Society of America   10.2138/rmg.2015.81.00  
Herzberg, C, Cabral RA, Jackson MG, Vidito C, Day JMD, Hauri EH.  2014.  Phantom Archean crust in Mangaia hotspot lavas and the meaning of heterogeneous mantle. Earth and Planetary Science Letters. 396:97-106.   10.1016/j.epsl.2014.03.065   Abstract

Lavas from Mangaia in the Cook–Austral island chain, Polynesia, define an HIMU (or high μ , where View the MathML source) global isotopic end-member among ocean island basalts (OIB) with the highest 206,207,208Pb/204Pb. This geochemical signature is interpreted to reflect a recycled oceanic crust component in the mantle source. Mass independently fractionated (MIF) sulfur isotopes indicate that Mangaia lavas sampled recycled Archean material that was once at the Earth's surface, likely hydrothermally-modified oceanic crust. Recent models have proposed that crust that is subducted and then returned to the surface in a mantle plume is expected to transform to pyroxenite/eclogite during transit through the mantle. Here we examine this hypothesis for Mangaia using high-precision electron microprobe analysis on olivine phenocrysts. Contrary to expectations of a crustal component and, hence pyroxenite, results show a mixed peridotite and pyroxenite source, with peridotite dominating. If the isotopic compositions were inherited from subduction of recycled oceanic crust, our work shows that this source has phantom-like properties in that it can have its lithological identity destroyed while its isotope ratios are preserved. This may occur by partial melting of the pyroxenite and injection of its silicic melts into the surrounding mantle peridotite, yielding a refertilized peridotite. Evidence from one sample reveals that not all pyroxenite in the melting region was destroyed. Identification of source lithology using olivine phenocryst chemistry can be further compromised by magma chamber fractional crystallization, recharge, and mixing. We conclude that the commonly used terms mantle “heterogeneities” and “streaks” are ambiguous, and distinction should be made of its lithological and isotopic properties.

Howarth, GH, Udry A, Day JMD.  2018.  Petrogenesis of basaltic shergottite Northwest Africa 8657: Implications for fO2 correlations and element redistribution during shock melting in shergottites. Meteoritics and Planetary Science. 53:249-267.   10.1111/maps.12999   AbstractWebsite

Northwest Africa (NWA) 8657 is an incompatible trace element-enriched, low-Al basaltic shergottite, similar in texture and chemistry to Shergotty, Zagami, and NWA 5298. It is composed of zoned pyroxene, maskelynite, merrillite, and Ti-oxide minerals with minor apatite, silica, and pyrrhotite. Pyroxene grains are characterized by patchy zoning, with pigeonite or augite cores zoned to Fe-rich pigeonite mantles. The cores have rounded morphologies and irregular margins. Combined with the low Ti/Al of the cores, the morphology and chemistry of the pyroxene grains are consistent with initial crystallization at depth (30–70 km) followed by partial resorption en route to the surface. Enriched rare earth element (REE) equilibrium melt compositions and calculated oxygen fugacities (fO2) conditions for pigeonite cores indicate that the original parent melts were enriched shergottite magmas that staged in chambers at depth within the Martian crust. NWA 8657 does not represent a liquid but rather entrained a proportion of pyroxene crystals from magma chambers where fractional crystallization was occurring at depth. Variation between fO2 and bulk-rock (La/Yb)N of the enriched and intermediate shergottites suggests that oxidation conditions and degree of incompatible element enrichment in the source may not be correlated, as thought previously. Shock melt pockets are characterized by an absence of phosphates and oxide minerals. It is likely that these phases were melted during shock. REEs were redistributed during this process into maskelynite and to a lesser extent the shock melt; however, the overall normalized REE profile of the shock melt is like that of the bulk-rock, but at lower absolute concentrations. Overall, shock melting has had a significant effect on the mineralogy of NWA 8657, especially the distribution of phosphates, which may be significant for geochronological applications of this meteorite and other Martian meteorites with extensive shock melt.

Howarth, GH, Day JMD, Pernet-Fisher JF, Goodrich CA, Pearson DG, Luo Y, Ryabov VV, Taylor LA.  2017.  Precious metal enrichment at low-redox in terrestrial native Fe-bearing basalts investigated using laser-ablation ICP-MS. Geochimica et Cosmochimica Acta.   10.1016/j.gca.2017.01.003   Abstract

Primary native Fe is a rare crystallizing phase from terrestrial basaltic magmas, requiring highly reducing conditions (fO2

Hyde, BC, Day JMD, Tait KT, Ash RD, Holdsworth DW, Moser DE.  2014.  Characterization of weathering and heterogeneous mineral phase distribution in brachinite Northwest Africa 4872. Meteoritics and Planetary Science. 49(7):1141-1156.   10.1111/maps.12320   Abstract

Terrestrial weathering of hot desert achondrite meteorite finds and heterogeneous phase distributions in meteorites can complicate interpretation of petrological and geochemical information regarding parent-body processes. For example, understanding the effects of weathering is important for establishing chalcophile and siderophile element distributions within sulfide and metal phases in meteorites. Heterogeneous mineral phase distribution in relatively coarsely grained meteorites can also lead to uncertainties relating to compositional representativeness. Here, we investigate the weathering and high-density (e.g., sulfide, spinel, Fe-oxide) phase distribution in sections of ultramafic achondrite meteorite Northwest Africa (NWA) 4872. NWA 4872 is an olivine-rich brachinite (Fo63.6 ± 0.5) with subsidiary pyroxene (Fs9.7 ± 0.1Wo46.3 ± 0.2), Cr-spinel (Cr# = 70.3 ± 1.1), and weathered sulfide and metal. Raman mapping confirms that weathering has redistributed sulfur from primary troilite, resulting in the formation of Fe-oxide (-hydroxide) and marcasite (FeS2). From Raman mapping, NWA 4872 is composed of olivine (89%), Ca-rich pyroxene (0.4%), and Cr-spinel (1.1%), with approximately 7% oxidized metal and sulfide and 2.3% marcasite-dominated sulfide. Microcomputed tomography (micro-CT) observations reveal high-density regions, demonstrating heterogeneities in mineral distribution. Precision cutting of the largest high-density region revealed a single 2 mm Cr-spinel grain. Despite the weathering in NWA 4872, rare earth element (REE) abundances of pyroxene determined by laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) indicate negligible modification of these elements in this mineral phase. The REE abundances of mineral grains in NWA 4872 are consistent with formation of the meteorite as the residuum of the partial melting process that occurred on its parent body. LA-ICP-MS analyses of sulfide and alteration products demonstrate the mobility of Re and/or Os; however, highly siderophile element (HSE) abundance patterns remain faithful recorders of processes acting on the brachinite parent body(ies). Detailed study of weathering and phase distribution offers a powerful tool for assessing the effects of low-temperature alteration and for identifying robust evidence for parent-body processes.

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Inglis, EC, Moynier F, Creech J, Deng Z, Day JMD, Teng F-Z, Bizzarro M, Jackson M, Savage P.  2019.  Isotopic fractionation of zirconium during magmatic differentiation and the stable isotope composition of the silicate Earth. Geochimica et Cosmochimica Acta. 250:311-323.   10.1016/j.gca.2019.02.010   Abstract

High-precision double-spike Zr stable isotope measurements (expressed as δ94/90ZrIPGP-Zr, the permil deviation of the 94Zr/90Zr ratio from the IPGP-Zr standard) are presented for a range of ocean island basalts (OIB) and mid-ocean ridge basalts (MORB) to examine mass-dependent isotopic variations of zirconium in Earth. Ocean island basalt samples, spanning a range of radiogenic isotopic flavours (HIMU, EM) show a limited range in δ94/90ZrIPGP-Zr (0.046 ± 0.037‰; 2sd, n = 13). Similarly, MORB samples with chondrite-normalized La/Sm of >0.7 show a limited range in δ94/90ZrIPGP-Zr (0.053 ± 0.040‰; 2sd, n = 8). In contrast, basaltic lavas from mantle sources that have undergone significant melt depletion, such as depleted normal MORB (N-MORB) show resolvable variations in δ94/90ZrIPGP-Zr, from −0.045 ± 0.018 to 0.074 ± 0.023‰. Highly evolved igneous differentiates (>65 wt% SiO2) from Hekla volcano in Iceland are isotopically heavier than less evolved igneous rocks, up to 0.53‰. These results suggest that both mantle melt depletion and extreme magmatic differentiation leads to resolvable mass-dependent Zr isotope fractionation. We find that this isotopic fractionation is most likely driven by incorporation of light isotopes of Zr within the 8-fold coordinated sites of zircons, driving residual melts, with a lower coordination chemistry, towards heavier values. Using a Rayleigh fractionation model, we suggest a αzircon-melt of 0.9995 based on the whole rock δ94/90ZrIPGP-Zr values of the samples from Hekla volcano (Iceland). Zirconium isotopic fractionation during melt-depletion of the mantle is less well-constrained, but may result from incongruent melting and incorporation of isotopically light Zr in the 8-fold coordinated M2 site of orthopyroxene. Based on these observations lavas originating from the effect of melt extraction from a depleted mantle source (N-MORB) or that underwent zircon saturation (SiO2 > 65 wt%) are removed from the dataset to give an estimate of the primitive mantle Zr isotope composition of 0.048 ± 0.032‰; 2sd, n = 48. These data show that major controls on Zr fractionation in the Earth result from partial melt extraction in the mantle and by zircon fractionation in differentiated melts. Conversely, fertile mantle is homogenous with respect to Zr isotopes. Zirconium mass-dependent fractionation effects can therefore be used to trace large-scale mantle melt depletion events and the effects of felsic crust formation.

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Kato, C, Moynier F, Valdes M, Dhaliwal JK, Day JMD.  2015.  Extensive volatile loss during formation and differentiation of the Moon. Nature Communications. 6(7617)   10.1038/ncomms8617   Abstract

Low estimated lunar volatile contents, compared with Earth, are a fundamental observation for Earth–Moon system formation and lunar evolution. Here we present zinc isotope and abundance data for lunar crustal rocks to constrain the abundance of volatiles during the final stages of lunar differentiation. We find that ferroan anorthosites are isotopically heterogeneous, with some samples exhibiting high d66Zn, along with alkali and magnesian suite samples. Since the plutonic samples were formed in the lunar crust, they were not subjected to degassing into vacuum. Instead, their compositions are consistent with enrichment of the silicate portions of the Moon in the heavier Zn isotopes. Because of the difference in d66Zn between bulk silicate Earth and lunar basalts and crustal rocks, the volatile loss likely occurred in two stages: during the proto-lunar disk stage, where a fraction of lunar volatiles accreted onto Earth, and from degassing of a differentiating lunar magma ocean, implying the possibility of isolated, volatile-rich regions in the Moon’s interior.

Korhonen, FJ, Saito S, Brown M, Siddoway CS, Day JMD.  2010.  Multiple Generations of Granite in the Fosdick Mountains, Marie Byrd Land, West Antarctica: Implications for Polyphase Intracrustal Differentiation in a Continental Margin Setting. Journal of Petrology. 51:627-670.   10.1093/petrology/egp093   AbstractWebsite

Production of granite in the middle to lower crust and emplacement into the middle to upper crust at convergent plate margins is the dominant mechanism of crustal differentiation. The Fosdick Mountains of West Antarctica host migmatitic paragneisses and orthogneisses corresponding to the middle to lower crust and granites emplaced as dikes, sills and small plutons, which record processes of intracrustal differentiation along the East Gondwana margin. U-Pb chronology on magmatic zircon from granites reveals emplacement at c. 358-336 Ma and c. 115-98 Ma, consistent with a polyphase tectonic evolution of the region during Devonian-Carboniferous continental arc activity and Cretaceous continental rifting. The gneisses and granites exposed in the Fosdick migmatite-granite complex were derived from Early Paleozoic quartzose turbidites of the Swanson Formation and Ford Granodiorite suite calc-alkaline plutonic rocks, both of which are widely distributed outside the Fosdick Mountains and have affinity with rock elsewhere in East Gondwana. Granites of both Carboniferous and Cretaceous age have distinct chemical signatures that reflect different melting reactions and accessory phase behavior in contrasting sources. Based on whole-rock major and trace element geochemistry and Sr-Nd isotope compositions, Carboniferous granites with low Rb/Sr are interpreted to be products of melting of the Ford Granodiorite suite. Extant mineral equilibria modeling indicates that the Ford Granodiorite suite compositions produce melt volumes > 10 vol. % at temperatures above biotite stability, involving the breakdown of hornblende + plagioclase, consistent with the high CaO and Na(2)O contents in the low Rb/Sr granites. The Carboniferous low Rb/Sr granites show a sequence from near-melt compositions to compositions with increasing amounts of early crystallized biotite and plagioclase and evidence for apatite dissolution in the source. Carboniferous granites derived from the Swanson Formation are scarce, suggesting that the significant quantities of melt produced from the now residual paragneisses were emplaced at shallower crustal levels than are now exposed. The Cretaceous granites are divided into two distinct groups. An older group of granites (c. 115-110 Ma) has compositions consistent with a dominant Ford Granodiorite source, and characteristics that indicate that they may be less evolved equivalents of the regionally exposed Byrd Coast Granite suite at higher crustal levels. The younger group of granites (c. 109-102 Ma) has distinct light rare earth element depleted signatures. The chemical and isotopic data suggest that these granites were derived from partial melting of both fertile and residual Swanson Formation and had low water contents, indicating that the source rocks may have been dehydrated prior to anatexis as the Byrd Coast Granite suite magmas were transferring through and accumulating at higher crustal levels. The Cretaceous granites derived from the Swanson Formation make up a prominent horizontally sheeted leucogranite complex. The accumulation of these melts probably facilitated melt-induced weakening of the crust during a well-documented transition from regional shortening to regional extension, the formation of a detachment structure, and rapid exhumation of the Fosdick migmatite-granite complex. These multiple episodes of melting along the East Gondwana margin resulted in initial stabilization of the continental crust in the Carboniferous and further intracrustal differentiation in the Cretaceous.

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Liu, Y, Spicuzza MJ, Craddock PR, Day JMD, Valley JW, Dauphas N, Taylor LA.  2010.  Oxygen and iron isotope constraints on near-surface fractionation effects and the composition of lunar mare basalt source regions. Geochimica Et Cosmochimica Acta. 74:6249-6262.   10.1016/j.gca.2010.08.008   AbstractWebsite

Oxygen and iron isotope analyses of low-Ti and high-Ti mare basalts are presented to constrain their petrogenesis and to assess stable isotope variations within lunar mantle sources. An internally-consistent dataset of oxygen isotope compositions of mare basalts encompasses five types of low-Ti basalts from the Apollo 12 and 15 missions and eight types of high-Ti basalts from the Apollo 11 and 17 missions. High-precision whole-rock delta(18)O values (referenced to VSMOW) of low-Ti and high-Ti basalts correlate with major-element compositions (Mg#, TiO(2), Al(2)O(3)). The observed oxygen isotope variations within low-Ti and high-Ti basalts are consistent with crystal fractionation and match the results of mass-balance models assuming equilibrium crystallization. Whole-rock delta(56)Fe values (referenced to IRMM-014) of high-Ti and low-Ti basalts range from 0.134 parts per thousand to 0.217 parts per thousand. and 0.038 parts per thousand, to 0.104 parts per thousand, respectively. Iron isotope compositions of both low-Ti and high-Ti basalts do not correlate with indices of crystal fractionation, possibly owing to small mineral-melt iron fractionation factors anticipated under lunar reducing conditions. The delta(18)O and delta(56)Fe values of low-Ti and the least differentiated high-Ti mare basalts are negatively correlated, which reflects their different mantle source characteristics (e.g., the presence or absence of ilmenite). The average delta(56)Fe values of low-Ti basalts (0.073 +/- 0.018 parts per thousand), n = 8) and high-Ti basalts (0.191 +/- 0.020 parts per thousand, n = 7) may directly record that of their parent mantle sources. Oxygen isotope compositions of mantle sources of low-Ti and high-Ti basalts are calculated using existing models of lunar magma ocean crystallization and mixing, the estimated equilibrium mantle olivine delta(18)O value, and equilibrium oxygen-fractionation between olivine and other mineral phases. The differences between the calculated whole-rock delta(18)O values for source regions, 5.57 parts per thousand for low-Ti and 5.30 parts per thousand for high-Ti mare basalt mantle source regions, are solely a function of the assumed source mineralogy. The oxygen and iron isotope compositions of lunar upper mantle can be approximated using these mantle source values. The delta(18)O and delta(56)Fe values of the lunar upper mantle are estimated to be 5.5 +/- 0.27. (2 sigma) and 0.085 +/- 0.040 parts per thousand (2 sigma), respectively. The oxygen isotope composition of lunar upper mantle is identical to the current estimate of Earth's upper mantle (5.5 0.2 parts per thousand), and the iron isotope composition of the lunar upper mantle overlaps within uncertainty of estimates for the terrestrial upper mantle (0.044 +/- 0.030 parts per thousand.). (C) 2010 Elsevier Ltd. All rights reserved.

Liu, Y, Floss C, Day JMD, Hill E, Taylor LA.  2009.  Petrogenesis of lunar mare basalt meteorite Miller Range 05035. Meteoritics & Planetary Science. 44:261-284. AbstractWebsite

Miller Range (MIL) 05035 is a low-Ti mare basalt that consists predominantly of pyroxene (62.3 vol%) and plagioclase (26.4 vol%). Pyroxenes are strongly shocked and complexly zoned from augite (Wo(33)) and pigeonite (Wo(17)) cores with Mg# = 50-54 to hedenbergite rims. Coexisting pyroxene core compositions reflect crystallization temperatures of 1000 to 1100 degrees C. Plagioclase has been completely converted to maskelynite with signs of recrystallization. Maskelynite is relatively uniform in composition (An(94)Ab(6)-An(91)Ab(9)), except at contacts with late-stage mesostasis areas (elevated K contents, An(82)Ab(15)Or(3)). Symplectites (intergrowth of Fe-augite, fayalite, and silica) of different textures and bulk compositions in MIL 05035 suggest formation by decomposition of Ferro-pyroxene during shock-induced heating, which is Supported by the total maskelynitization of plagioclase, melt pockets, and the presence of a relict pyroxferroite grain. Petrography and mineral chemistry imply that crystallization of MIL 05035 Occurred in the sequence of Fe-poor pyroxenes (Mg# = 50-54), followed by plagioclase and Fe-rich pyroxenes (Mg# = 20-50), and finally hedenbergite, Fe-Ti oxides, and minor late-stage phases. Petrography, bulk chemistry, mineral compositions, and the age of MIL 05035 Suggest it is possibly Source crater-paired with Asuka (A-) 881757 and Yamato (Y-) 793169, and may also be launch-paired with Meteorite Hills (MET) 01210. MIL 05035 represents an old (similar to 3.8-3.9 Ga), incompatible element-depleted low-Ti basalt that was not sampled during the Apollo or Luna missions. The light-REE depleted nature and lack of Eu anomalies For this meteorite are consistent with an origin distant from the Procellarum KREEP Terrane, and genesis from an early Cumulate mantle-source region generated by extensive differentiation of the Moon.

Lowder, KB, Allen MC, Day JMD, Deheyn DD, Taylor JRA.  2017.  Assessment of ocean acidification and warming on the growth, calcification, and biophotonics of a California grass shrimp. ICES Journal of Marine Science.   doi:10.1093/icesjms/fsw246   Abstract

Cryptic colouration in crustaceans, important for both camouflage and visual communication, is achieved through physiological and morphological mechanisms that are sensitive to changes in environmental conditions. Consequently, ocean warming and ocean acidification can affect crustaceans’ biophotonic appearance and exoskeleton composition in ways that might disrupt colouration and transparency. In the present study, we measured growth, mineralization, transparency, and spectral reflectance (colouration) of the caridean grass shrimp Hippolyte californiensis in response to pH and temperature stressors. Shrimp were exposed to ambient pH and temperature (pH 8.0, 17 °C), decreased pH (pH 7.5, 17 °C), and decreased pH/increased temperature (pH 7.5, 19 °C) conditions for 7 weeks. There were no differences in either Mg or Ca content in the exoskeleton across treatments nor in the transparency and spectral reflectance. There was a small but significant increase in percent growth in the carapace length of shrimp exposed to decreased pH/increased temperature. Overall, these findings suggest that growth, calcification, and colour of H. californiensis are unaffected by decreases of 0.5 pH units. This tolerance might stem from adaptation to the highly variable pH environment that these grass shrimp inhabit, highlighting the multifarious responses to ocean acidification, within the Crustacea.

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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.