^1,2Travis J.Tenner,^1,3Daisuke Nakashima,^1,4Takayuki Ushikubo,⁴Naotaka Tomioka,^5,6Makoto Kimura,^7,8Michael K.Weisberg,¹Noriko T.Kita
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.06.023]
¹WiscSIMS, Department of Geoscience, University of Wisconsin-Madison, Madison, WI 53706, USA
²Chemistry Division, Nuclear and Radiochemistry, Los Alamos National Laboratory, MSJ514, Los Alamos, NM 87545, USA
³Department of Earth and Planetary Material Sciences, Faculty of Science, Tohoku University, Aoba, Sendai, Miyagi 980-8578, Japan
⁴Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 200 Monobe Otsu, Nankoku, Kochi 783-8502, Japan
⁵Faculty of Science, Ibaraki University, Mito 310-8512, Japan
⁶National Institute of Polar Research, Tokyo 190-8518, Japan
⁷Kingsborough Community College and Graduate Center, The City University of New York, 2001 Oriental Boulevard, Brooklyn, NY 11235-2398, USA
⁸American Museum of Natural History, Central Park West at 79th Street, New York, NY, 10024-5192, USA
Copyright Elsevier

Al-Mg isotope systematics of twelve FeO-poor (type I) chondrules from CR chondrites Queen Alexandra Range 99177 and Meteorite Hills 00426 were investigated by secondary ion mass spectrometry (SIMS). Five chondrules with Mg#’s of 99.0 to 99.2 and Δ¹⁷O of −4.2‰ to −5.3‰ have resolvable excess ²⁶Mg. Their inferred (²⁶Al/²⁷Al)₀ values range from (3.5 ± 1.3) × 10⁻⁶ to (6.0 ± 3.9) × 10⁻⁶. This corresponds to formation times of 2.2 (–0.5/+1.1) Myr to 2.8 (−0.3/+0.5) Myr after CAIs, using a canonical (²⁶Al/²⁷Al)₀ of 5.23 × 10^-5, and assuming homogeneously distributed ²⁶Al that yielded a uniform initial ²⁶Al/²⁷Al in the Solar System. Seven chondrules lack resolvable excess ²⁶Mg. They have lower Mg#’s (94.2 to 98.7) and generally higher Δ¹⁷O (−0.9‰ to −4.9‰) than chondrules with resolvable excess ²⁶Mg. Their inferred (²⁶Al/²⁷Al)₀ upper limits range from 1.3 × 10⁻⁶ to 3.2 × 10⁻⁶, corresponding to formation >2.9 to >3.7 Myr after CAIs. Al-Mg isochrons depend critically on chondrule plagioclase, and several characteristics indicate the chondrule plagioclase is unaltered: (1) SIMS ²⁷Al/²⁴Mg depth profile patterns match those from anorthite standards, and SEM/EDS of chondrule SIMS pits show no foreign inclusions; (2) transmission electron microscopy (TEM) reveals no nanometer-scale micro-inclusions and no alteration due to thermal metamorphism; (3) oxygen isotopes of chondrule plagioclase match those of coexisting olivine and pyroxene, indicating a low extent of thermal metamorphism; and (4) electron microprobe data show chondrule plagioclase is anorthite-rich, with excess structural silica and high MgO, consistent with such plagioclase from other petrologic type 3.00-3.05 chondrites. We conclude that the resolvable (²⁶Al/²⁷Al)₀ variabilities among chondrules studied are robust, corresponding to a formation interval of at least 1.1 Myr.

Using relationships between chondrule (²⁶Al/²⁷Al)₀, Mg#, and Δ¹⁷O, we interpret spatial and temporal features of dust, gas, and H₂O ice in the FeO-poor chondrule-forming environment. Mg# ≥ 99, Δ¹⁷O ∼−5‰ chondrules with resolvable excess ²⁶Mg initially formed in an environment that was relatively anhydrous, with a dust-to-gas ratio of ∼100×. After these chondrules formed, we interpret a later influx of ¹⁶O-poor H₂O ice into the environment, and that dust-to-gas ratios expanded (100× to 300×). This led to the later formation of more oxidized Mg# 94-99 chondrules with higher Δ¹⁷O (−5‰ to –1‰), with low (²⁶Al/²⁷Al)₀, and hence no resolvable excess ²⁶Mg.

We refine the mean CR chondrite chondrule formation age via mass balance, by considering that Mg# ≥ 99 chondrules generally have resolved positive (²⁶Al/²⁷Al)₀ and that Mg# < 99 chondrules generally have no resolvable excess ²⁶Mg, implying lower (²⁶Al/²⁷Al)₀. We obtain a mean chondrule formation age of 3.8 ± 0.3 Myr after CAIs, which is consistent with Pb-Pb and Hf-W model ages of CR chondrite chondrule aggregates. Overall, this suggests most CR chondrite chondrules formed immediately before parent body accretion.

¹T.J.Barrett,^1,2J.J.Barnes,^1,3M.Anand,¹I.A.Franchi,¹R.C.Greenwood,^1,4B.L.A.Charlier,¹X.Zhao,⁵F.Moynier,^1,3M.M.Grady
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.06.024]
¹School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
²Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX 77058, USA
³Department of Earth Sciences, Natural History Museum, London, SW7 5BD, UK
⁴Victoria University of Wellington, Wellington 6140, NZ
⁵Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Univeristé Paris Diderot, 75005 Paris, France
Copyright Elsevier

Generally, terrestrial rocks, martian and chondritic meteorites exhibit a relatively narrow range in bulk and apatite Cl isotope compositions, with δ³⁷Cl (per mil deviation from standard mean ocean chloride) values between − 5.6 and + 3.8 ‰. Lunar rocks, however, have more variable bulk and apatite δ³⁷Cl values, ranging from ∼ − 4 to + 40 ‰. As the Howardite-Eucrite-Diogenite (HED) meteorites represent the largest suite of crustal and sub-crustal rocks available from a differentiated basaltic asteroid (4 Vesta), studying them for their volatiles may provide insights into planetary differentiation processes during the earliest Solar System history.

Here the abundance and isotopic composition of Cl in apatite were determined for seven eucrites representing a broad range of textural and petrological characteristics. Apatite Cl abundances range from ∼ 25 to 4900 ppm and the δ³⁷Cl values range from − 3.98 to + 39.2 ‰. Samples with lower apatite H₂O contents were typically also enriched in ³⁷Cl but no systematic correlation between δ³⁷Cl and δD values was observed across samples. Modelled Rayleigh fractionation and a strong positive correlation between bulk δ⁶⁶Zn and apatite δ³⁷Cl support the hypothesis that Cl degassed as metal chlorides from eucritic magmas, in a hydrogen-poor environment. In the case of lunar samples, it has been noted that δ³⁷Cl values of apatite positively correlate with bulk La/Yb ratio. Interestingly, most eucrites show a negative correlation with bulk La/Yb ratio. Recently, isotopically light Cl values have been suggested to record the primary solar nebular signature. If this is the case then 4 Vesta, which accreted rapidly and early in Solar System history, could also record this primary nebular signature corresponding to the lightest Cl values measured here. The significant variation in Cl isotope composition observed within the eucrites are likely related to degassing of metal chlorides.

¹Josh Wimpenny et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.06.016]
¹Lawrence Livermore National Laboratory, Livermore, CA, 94550
Copyright Elsevier

Zinc isotopes fractionate during evaporation, and thus can potentially be used to calculate the proportion of volatile elemental loss from objects such as tektites, nuclear fallout melt glasses formed from silicate soils, and rocks from the Moon. The utility of the Zn isotope system in constraining the magnitude of volatile loss depends on accurate knowledge of its fractionation behavior during evaporation, i.e., the Zn isotope fractionation factor. Here, we present new results of Zn isotope analyses of experimentally heated soil samples, together with analyses of environmentally derived fallout melt glasses, and australite tektites, to better constrain how and to what extent Zn isotopes fractionate during thermally-driven evaporation.

Major and trace element analyses of melt glass derived from the experimental heating of rhyolitic and arkosic soils demonstrates that elemental fractionation progressively becomes more important with increasing temperature and time. Initial Zn isotope ratios in the rhyolitic and arkosic soils are similar to upper continental crustal (UCC) values but become increasingly isotopically heavy as more Zn is lost from the heated glass, with a maximum δ⁶⁶Zn value of +1.49 ± 0.05 ‰. The progressive loss of Zn from the rhyolitic soil is consistent with a fractionation factor (α) of 0.99879 ± 13. After loss of a labile component from the arkosic soil further evaporative loss of Zn from the silicate rich residue is also consistent with an α of ∼0.9988. This fractionation factor is not sensitive to either the heating temperature or duration.

The fallout melt glass, derived from near surface nuclear weapons tests, and natural tektite samples are both relatively enriched in isotopically heavy Zn compared to the UCC. Although the fallout melt glass is largely comprised of the same rhyolitic soil used in our experiments the extent of Zn isotope fractionation is lower; consistent with an α of 0.9997. This is similar to estimated values of α associated with loss of Zn from Trinitite and lunar rocks. It is more difficult to constrain a value for α from australite tektites because the location of the impact site is not well constrained. Based on our analyses, we estimate a range of α values between 0.9988-0.9997, which is broadly consistent with experimental data and analyses of fallout melt glass.

In all cases the measured Zn isotope fractionation factors are much lower than would be expected from evaporative loss of Zn in a high vacuum. We hypothesize that, for Zn, the value of α is dependent on the localized gas pressure and composition, with the degree of isotopic fractionation decreasing from high vacuum (< 1×10^-9 bar) to atmospheric pressure. This would have consequences for the interpretation of Zn systematics on the Moon. Recent studies suggest that Zn loss from the Moon was dominantly caused by the Giant Impact and proceeded with an α of ∼0.9997. If correct, and taken together with our experimental data, this suggests that evaporative loss of Zn from the Moon is unlikely to have occurred in high vacuum and is more likely to have taken place at pressures similar to or higher than the current terrestrial atmosphere.

¹Pechersky,¹D.M., Markov, G.P.
Izvestiya, Physics of the Solid Earth 55, 287-297 Link to Article [DOI: 10.1134/S1069351319020083]
¹Schmidt Institute of Physics of the Earth, Russian Academy of Sciences (IPE RAS), Moscow, 123242, Russian Federation

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

^1,2F. Thiessen,^1,3A. A. Nemchin,^1,4J. F. Snape,^1,2M. J. Whitehouse
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13310]
¹Department of Geosciences, Swedish Museum of Natural History, SE‐104 05 Stockholm, Sweden
²Department of Geological Sciences, Stockholm University, SE‐106 91 Stockholm, Sweden
³Department of Applied Geology, Curtin University, Perth, WA, 6845 Australia
⁴Faculty of Earth and Life Sciences, VU Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, the Netherlands
Published by arrangement with John Wiley & Sons

U‐Pb ages of zircon in four different Apollo 14 breccias (14305, 14306, 14314, and 14321) were obtained by secondary ion mass spectrometry. Some of the analyzed grains occur as cogenetic, poikilitic zircon grains in lithic clasts, revealing magmatic events at ~4286 Ma, ~4200–4220 Ma, and ~4150 Ma. The age distribution of the crystal clasts in the breccias exhibits a minor peak at ~4210 Ma, which can be attributed to a magmatic event, as recorded in zircon grains located in noritic clasts. An age peak at ~4335 Ma is present in all four breccias, as well as zircon grains from different Apollo landing sites, enhancing the confidence that these grains recorded a global zircon‐forming event. The overall age distribution among the four breccias exhibits minor differences between the breccias collected farther away from the Cone Crater and the ones collected within the continuous ejecta blanket of the Cone Crater. A granular zircon grain yielded a ²⁰⁷Pb/²⁰⁶Pb age of 3936 ± 8 Ma, which is interpreted as an impact event. A similar age of 3941 ± 5 Ma (n = 17, MSWD = 0.89, P = 0.58) was obtained for a large zircon grain (~430 × 340 μm in size). This grain might have crystallized in the same impact melt sheet which formed the granular zircon or the age is representative of the final extrusion of KREEP magma. The majority of zircon grains, however, occur as isolated crystal clasts within the matrix and their ages cannot be correlated with any real events (impact or magmatic) nor can the possibility be excluded that these ages represent partial resetting of the U‐Pb system.

^1,2Makiko K. Haba,¹Jörn-Frederik Wotzlaw,^1,3Yi-Jen Lai,⁴Akira Yamaguchi,¹Maria Schönbächler
Nature Geoscience (in Press) Link to Article [DOI
https://doi.org/10.1038/s41561-019-0377-8]
¹ETH Zürich, Institute of Geochemistry and Petrology, Zürich, Switzerland
²Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo, Japan
³Macquarie GeoAnalytical, Department of Earth and Planetary Sciences, Macquarie University, Sydney, New South Wales, Australia
⁴National Institute of Polar Research, Tokyo, Japan

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

^1,2Ninja Braukmüller,^1,2Frank Wombacher,^1,2Claudia Funk,^1,2Carsten Münker
Nature Geoscience (in Press) Link to Article [DOI
https://doi.org/10.1038/s41561-019-0375-x]
¹Institut für Geologie und Mineralogie, Universität zu Köln, Köln, Germany
²Steinmann Institut für Geologie, Mineralogie und Paläontologie, Universität Bonn, Poppelsdorfer Schloss, Bonn, Germany

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

^1,2Cheng Zhu,^1,2Parker B. Crandall,³Jeffrey J. Gillis-Davis,³Hope A. Ishii,⁴John P. Bradley,³Laura M. Corley,¹Ralf I. Kaiser
Proceeding sof the National Academy of Sciences of the United States of America 116, 11165-11170 Link to Article [https://doi.org/10.1073/pnas.1819600116]
¹Department of Chemistry, University of Hawai‘i at Mānoa, Honolulu, HI 96822;bW. M. Keck Laboratory in Astrochemistry, University of Hawai‘i at Mānoa, Honolulu, HI 96822;
²W. M. Keck Laboratory in Astrochemistry, University of Hawai‘i at Mānoa, Honolulu, HI 96822;
³Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, HI 96822

The source of water (H₂O) and hydroxyl radicals (OH), identified on the lunar surface, represents a fundamental, unsolved puzzle. The interaction of solar-wind protons with silicates and oxides has been proposed as a key mechanism, but laboratory experiments yield conflicting results that suggest that proton implantation alone is insufficient to generate and liberate water. Here, we demonstrate in laboratory simulation experiments combined with imaging studies that water can be efficiently generated and released through rapid energetic heating like micrometeorite impacts into anhydrous silicates implanted with solar-wind protons. These synergistic effects of solar-wind protons and micrometeorites liberate water at mineral temperatures from 10 to 300 K via vesicles, thus providing evidence of a key mechanism to synthesize water in silicates and advancing our understanding on the origin of water as detected on the Moon and other airless bodies in our solar system such as Mercury and asteroids.

^1,2Alex W. R. Bevan,¹Peter J. Downes,³Dermot A. Henry,⁴Michael Verrall,⁵Peter W. Haines
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13307]
¹Department of Earth and Planetary Sciences, Western Australian Museum, Locked Bag 49, Welshpool DC, Western Australia, 6986 Australia
²Department of Imaging and Applied Physics, Curtin University, GPO Box U1987, Western Australia, 6845 Australia
³Geosciences Department, Museum Victoria, GPO Box 666, Melbourne, Victoria, 3001 Australia
⁴CSIRO Mineral Resources, Australian Resources Research Centre, 26 Dick Perry Avenue, Technology Park, Kensington, Western Australia, 6151 Australia
⁵Geological Survey of Western Australia, Department of Mines, Industry Regulation and Safety, 100 Plain Street, East Perth, Western Australia, 6004 Australia
Published by arrangement with John Wiley & Sons

On February 24, 1979, a deeply oxidized mass of iron meteorite was excavated from bauxite at an open cut mine on the Gove Peninsula, Northern Territory, Australia. The meteorite, measuring 0.75–1 m in diameter and of unknown total weight, was found at coordinates 12°15.8′S, 136°50.3′E. On removal from the ground, the meteorite is reported to have disintegrated rapidly. A preliminary analysis at the mine laboratory reportedly gave 8.5 wt% Ni. A modern analysis of oxidized material gave Ni = 32.9, Co = 3.67 (both mg g⁻¹), Cr = 168, Cu = 195, Ga = 22.5, Ge = <70, As = 4.16, W = 1.35, Ir = 10.5, Pt = 21.2, Au = 0.672 (all μg g⁻¹), Sb = <150, and Re = 844 (both ng g⁻¹). Competent fragments of oxidized material retain a fine to medium Widmanstätten pattern with an apparent average bandwidth of 0.5 mm (range 0.2–0.9 mm in plane section). Primary mineralogy includes rare γ–taenite and daubréelite, and secondary minerals produced by weathering include awaruite (with up to 78.5 wt% Ni) and an, as yet, unnamed Cu‐Cr‐bearing sulfide with the ideal formula CuCrS₂ that is hitherto unknown in nature. Deep weathering has masked many of the features of the meteorite; however, the analysis normalized to the analyses of fresh iron meteorites favors chemical group IIIAB. The terrestrial age of the meteorite is unknown, although it is likely to be in the Neogene (2.5–23 Ma), which is widely accepted as the major period of bauxite formation in the Northern Territory of Australia. Gove is the second authenticated relict meteorite found in Australia.

^1,2,3Luke Daly et al. (>10)
Earth and Planetary Science Letters 220-230 Link to Article [https://doi.org/10.1016/j.epsl.2019.05.050]
¹School of Geographical and Earth Sciences, University of Glasgow, Glasgow, G12 8QQ, UK
²Space Science and Technology Centre, School of Earth and Planetary Sciences, Curtin University, GPO Box U1987, Perth, WA 6845, Australia
³Australian Centre for Microscopy and Microanalysis, University of Sydney, Sydney 2006, NSW, Australia
Copyright Elsevier

In order to validate calculated ages of the Martian crust we require precise radiometric dates from igneous rocks where their provenance on the Martian surface is known. Martian meteorites have been dated precisely and quantitatively, but the launch sites are currently unknown. Inferring the formation environment of a correlated suite of Martian meteorites can constrain the nature and complexity of the volcanic system they formed from. The nakhlite meteorites are such a suite of augite-rich rocks that sample the basaltic crust of Mars, and as such can provide unique insights into its volcanic processes. Using electron backscatter diffraction we have determined the shape-preferred and crystallographic-preferred orientation petrofabrics of four nakhlites (Governador Valadares, Lafayette, Miller Range 03346 and Nakhla) in order to understand the conditions under which their parent rocks formed. In all samples, there is a clear link between the shape-preferred orientation (SPO) and crystallographic-preferred orientation (CPO) of augite phenocrysts. This relationship reveals the three-dimensional shape of the augite crystals using CPO as a proxy for 3D SPO, and also enables a quantitative 3-dimensional petrofabric analysis. All four nakhlites exhibit a foliation defined by the CPO of the augite <c> axis in a plane, although individual meteorites show subtle textural variations. Nakhla and Governador Valadares display a weak CPO lineation within their <c> axis foliation that is interpreted to have developed in a combined pure shear/simple shear flow regime, indicative of emplacement of their parent rock as a subaerial hyperbolic lava flow. By contrast, the foliation dominated CPO petrofabrics of Lafayette and Miller Range 03346 suggest formation in a pure shear dominated regime with little influence of hyperbolic flow. These CPO petrofabrics are indicative of crystal settling in the stagnant portion of cooling magma bodies, or the flattening area of spreading lava flows. The CPO foliation of Lafayette’s is substantially weaker than Miller Range 03346, probably due to its higher phenocryst density causing grain-grain interactions that hindered fabric development. The CPO petrofabrics identified can also be used to determine the approximate plane of the Martian surface and the line of magma flow to within ∼20°. Our results suggest that the nakhlite launch crater sampled a complex volcanic edifice that was supplied by at least three distinct magmatic systems limiting the possible locations these rocks could have originated from on Mars.