¹J.J. Bellucci, ^1,2A.A. Nemchin, ¹M.J. Whitehouse, ¹J.F. Snape, ²P. Bland, ²G.K. Benedix, ³J. Roszjar
Earth and Planetary Science Letters 485, 79-87 Link to Article [https://doi.org/10.1016/j.epsl.2017.12.039]
¹Department of Geosciences, Swedish Museum of Natural History, SE-104 05, Stockholm, Sweden
²Department of Applied Geology, Curtin University, Perth, WA 6845, Australia
³Department of Mineralogy and Petrography, Natural History Museum Vienna, Burgring 7, 1010, Vienna, Austria
Copyright Elsevier

The initial Pb compositions of one enriched shergottite, one intermediate shergottite, two depleted shergottites, and Nakhla have been measured by Secondary Ion Mass Spectrometry (SIMS). These values, in addition to data from previous studies using an identical analytical method performed on three enriched shergottites, ALH 84001, and Chassigny, are used to construct a unified and internally consistent model for the differentiation history of the Martian mantle and crystallization ages for Martian meteorites. The differentiation history of the shergottites and Nakhla/Chassigny are fundamentally different, which is in agreement with short-lived radiogenic isotope systematics. The initial Pb compositions of Nakhla/Chassigny are best explained by the late addition of a Pb-enriched component with a primitive, non-radiogenic composition. In contrast, the Pb isotopic compositions of the shergottite group indicate a relatively simple evolutionary history of the Martian mantle that can be modeled based on recent results from the Sm–Nd system. The shergottites have been linked to a single mantle differentiation event at 4504 Ma. Thus, the shergottite Pb isotopic model here reflects a two-stage history 1) pre-silicate differentiation (4504 Ma) and 2) post-silicate differentiation to the age of eruption (as determined by concordant radiogenic isochron ages). The μ-values (²³⁸U/²⁰⁴Pb) obtained for these two different stages of Pb growth are μ₁ of 1.8 and a range of μ₂ from 1.4–4.7, respectively. The μ₁-value of 1.8 is in broad agreement with enstatite and ordinary chondrites and that proposed for proto Earth, suggesting this is the initial μ-value for inner Solar System bodies. When plotted against other source radiogenic isotopic variables (Sr_i, γ¹⁸⁷Os, ε¹⁴³Nd, and ε¹⁷⁶Hf), the second stage mantle evolution range in observed mantle μ  -values display excellent linear correlations (r²>0.85) and represent a spectrum of Martian mantle mixing-end members (depleted, intermediate, enriched).

^1,2Yunzhao Wu, ³Bruce Hapke
Earth and Planetary Science Letters 484, 145-153 Link to Article [https://doi.org/10.1016/j.epsl.2017.12.003]
¹Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210034, China
²Space Science Institute, Macau University of Science and Technology, Macau, China
³Department of Geology and Environmental Science, University of Pittsburgh, Pittsburgh, PA, USA
Copyright Elsevier

The Moon’s reflectance spectrum records many of its important properties. However, prior to Chang’E-3 (CE-3), no spectra had previously been measured on the lunar surface. Here we show the in situ reflectance spectra of the Moon acquired on the lunar surface by the Visible-Near Infrared Spectrometer (VNIS) onboard the CE-3 rover. The VNIS detected thermal radiation from the lunar regolith, though with much shorter wavelength range than typical thermal radiometer. The measured temperatures are higher than expected from theoretical model, indicating low thermal inertia of the lunar soil and the effects of grain facet on soil temperature in submillimeter scale. The in situ spectra also reveal that 1) brightness changes visible from orbit are related to the reduction in maturity due to the removal of the fine and weathered particles by the lander’s rocket exhaust, not the smoothing of the surface and 2) the spectra of the uppermost soil detected by remote sensing exhibit substantial differences with that immediately beneath, which has important implications for the remote compositional analysis. The reflectance spectra measured by VNIS not only reveal the thermal, compositional, and space-weathering properties of the Moon but also provide a means for the calibration of optical instruments that view the surface remotely.

^1,2Philip J.Carter, ¹Zoë M.Leinhardt, ³Tim Elliott, ²Sarah T.Stewart, ³Michael J.Walter
Earth and Planetary Science Letters 484, 276-286 Link to Article [https://doi.org/10.1016/j.epsl.2017.12.012]
¹School of Physics, University of Bristol, H. H. Wills Physics Laboratory, Tyndall Avenue, Bristol BS8 1TL, UK
²Department of Earth and Planetary Sciences, University of California Davis, One Shields Avenue, Davis, CA 95616, USA
³School of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol BS8 1RJ, UK
Copyright Elsevier

Geochemical studies of planetary accretion and evolution have invoked various degrees of collisional erosion to explain differences in bulk composition between planets and chondrites. Here we undertake a full, dynamical evaluation of ‘crustal stripping’ during accretion and its key geochemical consequences. Crusts are expected to contain a significant fraction of planetary budgets of incompatible elements, which include the major heat producing nuclides. We present smoothed particle hydrodynamics simulations of collisions between differentiated rocky planetesimals and planetary embryos. We find that the crust is preferentially lost relative to the mantle during impacts, and we have developed a scaling law based on these simulations that approximates the mass of crust that remains in the largest remnant. Using this scaling law and a recent set of N-body simulations of terrestrial planet formation, we have estimated the maximum effect of crustal stripping on incompatible element abundances during the accretion of planetary embryos. We find that on average approximately one third of the initial crust is stripped from embryos as they accrete, which leads to a reduction of ∼20% in the budgets of the heat producing elements if the stripped crust does not reaccrete. Erosion of crusts can lead to non-chondritic ratios of incompatible elements, but the magnitude of this effect depends sensitively on the details of the crust-forming melting process on the planetesimals. The Lu/Hf system is fractionated for a wide range of crustal formation scenarios. Using eucrites (the products of planetesimal silicate melting, thought to represent the crust of Vesta) as a guide to the Lu/Hf of planetesimal crust partially lost during accretion, we predict the Earth could evolve to a superchondritic 176Hf/177Hf (3–5 parts per ten thousand) at present day. Such values are in keeping with compositional estimates of the bulk Earth. Stripping of planetary crusts during accretion can lead to detectable changes in bulk composition of lithophile elements, but the fractionation is relatively subtle, and sensitive to the efficiency of reaccretion.

¹Qin Zhou,²Qing-Zhu Yin,³Charles K. Shearer,⁴Xian-Hua Li,⁴Qiu-Li Li,⁴Yu Liu,⁴Guo-Qiang Tang,¹Chun-Lai Li
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13026]
¹Key Laboratory of Lunar and Deep Space Exploration, National Astronomical Observatories, Chinese Academy of Sciences, Beijing, China
²Department of Earth and Planetary Sciences, University of California Davis, Davis, California, USA
³Department of Earth and Planetary Sciences, Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico, USA
⁴State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
Published by arrangement with John Wiley & Sons

The Antarctic achondrite Graves Nunataks 06128 (GRA 06128) and Graves Nunataks 06129 (GRA 06129) represent a unique high-temperature, nonbasaltic magmatism in the early solar system. These objects have been interpreted as products of low-degree partial melting of volatile-rich chondritic material, which may have been the asteroid parent bodies of brachinite. Previous studies have investigated their crystallization and metamorphic history with various isotope systematics. Here, we report the U-Pb intercept age of 4466 ± 29 Ma and the weighted-average 207Pb-206Pb age of 4460 ± 30 Ma for the Cl-apatite grains from GRA 06129. Our apatite ages are obviously younger than that of the 26Al-26Mg model age (4565.9 ± 0.3 Ma; Shearer et al. 2010a), but are the same as the 40Ar-39Ar age obtained via step-heating of the bulk rock (4460 ± 28 Ma; Fernandes and Shearer 2010; Shearer et al. 2010a). Based on petrographic observations, merrillites are usually rimmed by apatite and exist as inclusions in apatite. Therefore, the apatite U-Pb age from GRA 06129 probably records a metamorphic event of replacing merrillite with apatite, caused by Cl-rich melts or fluids on their parent body. A collisional event has provided the impact heating for this metamorphic event. Increasing amounts of geochronologic evidence show that the giant impact of the Moon-forming event has affected the asteroid belt at 4450–4470 Ma (Bogard and Garrison 2009; Popova et al. 2013; Yin et al. 2014; Zhang et al. 2016). Considering the contemporary metamorphic events for GRA 06129 (4460 ± 30 Ma), it is likely that the asteroid parent body of GRA 06129 was also affected by the same giant impact as the Moon-forming event.

¹Timothy M. Hahn Jr.,^1,2Nicole G. Lunning,¹Harry Y. McSween Jr.,³Robert J. Bodnar,¹Lawrence A. Taylor
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13036]
¹Department of Earth and Planetary Sciences and Planetary Geoscience Institute, University of Tennessee, Knoxville, Tennessee, USA
²Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D.C., USA
³Department of Geosciences, Virginia Tech, Blacksburg, Virginia, USA
Published by arrangement with John Wiley & Sons

We describe petrographic, electron microprobe, and laser ablation ICP-MS analyses of Mg-rich harzburgite clasts in the Dominion Range 2010 howardites, and conclude that they are xenolithic samples of the vestan mantle. Key chemical and petrologic characteristics of these rocks provide tests for differentiation models. Our results indicate the mantle of Vesta formed through variable degrees of partial melting, which left behind a harzburgite and possibly dunite residuum. The Mg-rich clasts are composed of orthopyroxene and olivine, with minor clinopyroxene, FeNi metal, and distinctive pyroxene–chromite symplectites. We use mineral chemistry to demonstrate the absence of a genetic link between diogenites and the Mg-rich harzburgites. We propose a secondary origin for the formation of symplectites: interaction of silicate and metallic melts during primordial differentiation and core formation. The occurrence of FeNi metal containing ~1.5 wt% Cr within the assemblage indicates a very reducing environment during mantle differentiation (≪IW). Our study suggests that Vesta did not experience complete melting early in its history, and instead supports the formation of a shallow magma ocean.

¹P. Oliver,¹M. Ralchenko,¹C. Samson,^1,2R. E. Ernst,³P. J. A. McCausland,⁴G. F. West
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13028]
¹Department of Earth Sciences, Carleton University, Ottawa, Ontario, Canada
²Faculty of Geology and Geography, Tomsk State University, Tomsk, Russia
³Western Paleomagnetic and Petrophysical Laboratory, Western University, London, Ontario, Canada
⁴Department of Physics, University of Toronto, Toronto, Ontario, Canada
Published by arrangement with John Wiley & Sons

Ordinary chondrites have previously been nondestructively characterized using bulk magnetic susceptibility, broadly reflecting their Fe-Ni alloy content. We seek to expand the information that can be recovered from magnetic susceptibility by using the University of Toronto Electromagnetic Induction Spectrometer (UTEMIS) to measure the complex magnetic susceptibility tensor of 20 ordinary chondrites samples in addition to 16 Gao–Guenie (H5) chondrites at 35 frequencies from 90 Hz to 64 kHz, at variable low applied field strengths <10 A m−1. Following removal of the field-dependent component of susceptibility, frequency dependence, in- and out-of-phase components, and bulk magnetic susceptibility were interpreted. Most meteorites showed no frequency-dependent in-phase responses, but had a frequency-dependent out-of-phase response attributed to eddy currents induced in conductive minerals. Greater in- and out-of-phase frequency dependence correlated with lower fayalite content in olivine and was, in turn, inversely proportional to Fe-Ni alloy content. The uncertainty in the UTEMIS measurements ranges from approximately 0.05% for low-frequency in-phase measurements to a maximum of 3% for low-frequency out-of-phase measurements. This uncertainty level was far lower than the intra-meteorite variability for the Gao–Guenie suite suggesting inhomogeneity at scales of approximately 10 g.

¹C.M.Pieters et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13008]
¹Brown University, Providence, Rhode Island, USA
Published by arrangement with John Wiley & Sons

The geologic context of red organic-rich materials (ROR) found across an elongated 200 km region on Ceres is evaluated with spectral information from the multispectral framing camera (FC) and the visible and near-infrared mapping spectrometer (VIR) of Dawn. Discrete areas of ROR materials are found to be associated with small fresh craters less than a few hundred meters in diameter. Regions with the highest concentration of discrete ROR areas exhibit a weaker diffuse background of ROR materials. The observed pattern could be consistent with a field of secondary impacts, but no appropriate primary crater has been found. Both endogenic and exogenic sources are being considered for these distinctive organic materials.

^1,2Matthias Ebert,^2,3Astrid Kowitz,²Ralf Thomas Schmitt,^2,4,5Wolf Uwe Reimold,⁶Ulrich Mansfeld,⁶Falko Langenhorst
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12948]
¹Institut für Geo- und Umweltnaturwissenschaften, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
²Museum für Naturkunde – Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany
³Department of Earth Sciences, Freie Universität, Berlin, Germany
⁴Humboldt Universität zu Berlin, Berlin, Germany
⁵Geochronology Laboratory, University of Brasilia, Brasilia, Brazil
⁶Institut für Geowissenschaften, Friedrich-Schiller-Universität Jena, Jena, Germany
Published by arrangement with John Wiley & Sons

Shock-induced recovery experiments were performed to investigate melt formation in porous sandstones in the low shock pressure regime between 2.5 and 17.5 GPa. The sandstone shocked at 2.5 and 5 GPa is characterized by pore closure, fracturing of quartz (Qtz), and compression and deformation of phyllosilicates; no melting was observed. At higher pressures, five different types of melts were generated around pores and alongside fractures in the sandstone. Melting of kaolinite (Kln), illite (Ill), and muscovite (Ms) starts at 7.5, 12, and 15 GPa, respectively. The larger the amount of water in these minerals (Kln ~14 wt%, Ill ~6–10 wt%, and Ms ~4 wt% H₂O), the higher the shock compressibility and the lower the shock pressure required to induce melting. Vesicles in the almost dry silicate glasses attest to the loss of structural water during the short shock duration of the experiment. The compositions of the phyllosilicate-based glasses are identical to the composition of the parental minerals or their mixtures. Thus, this study has demonstrated that phyllosilicates in shocked sandstone undergo congruent melting during shock loading. In experiments at 10 GPa and higher, iron melt from the driver plate was injected into the phyllosilicate melts. During this process, Fe is partitioned from the metal droplets into the surrounding silicate melts, which induced unmixing of silicate melts with different chemical properties (liquid immiscibility). At pressures between 7.5 and 15 GPa, a pure SiO₂ glass was formed, which is located as short and thin bands within Qtz grains. These bands were shown to contain tiny crystals of experimentally generated stishovite.

^1,2,3David Kaeter,¹Martin A. Ziemann,²Ute Böttger,⁴Iris Weber,⁵Lutz Hecht,⁶Sergey A. Voropaev,⁶Alexander V. Korochantsev,⁷Andrey V. Kocherov
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13027]
¹Institute for Earth and Environmental Sciences, University of Potsdam, Potsdam, Germany
²Institute of Optical Sensor Systems, German Aerospace Center, Berlin, Germany
³iCRAG, School of Earth Sciences, University College Dublin, Dublin D04 N2E5, Ireland
⁴Institute of Planetology, University of Münster, Münster, Germany
⁵Museum für Naturkunde, Berlin, Germany
⁶Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, Russia
⁷Chelyabinsk State University, Chelyabinsk, Russia
Published by arrangement with John Wiley & Sons

We present results of petrographic, mineralogical, and chemical investigations of three Chelyabinsk meteorite fragments. Three distinct lithologies were identified: light S3 LL5, dark S4–S5 LL5 material, and opaque fine-grained former impact melt. Olivine–spinel thermometry revealed an equilibration temperature of 703 ± 23 °C for the light lithology. All plagioclase seems to be secondary, showing neither shock-induced fractures nor sulfide-metal veinlets. Feldspathic glass can be observed showing features of extensive melting and, in the dark lithology, as maskelynite, lacking melt features and retaining grain boundaries of former plagioclase. Olivine of the dark lithology shows planar deformation features. Impact melt is dominated by Mg-rich olivine and resembles whole-rock melt. Melt veins (<2 mm) are connected to narrower veinlets. Melt vein textures are similar to pegmatite textures showing chilled margins, a zone of inward-grown elongated crystals and central vugs, suggesting crystallization from supercooled melt. Sulfide-metal droplets indicate liquid immiscibility of both silicate and sulfide as well as sulfide and metal melts. Impact melting may have been an important factor for differentiation of primitive planetary bodies. Graphite associated with micrometer-sized melt inclusions in primary olivine was detected by Raman mapping. Carbon isotopic studies of graphite could be applied to test a possible presolar origin.

¹F. A. J. Abernethy,¹A. B. Verchovsky,¹I. A. Franchi,^1,2M. M. Grady
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13016]
¹Planetary and Space Sciences, The Open University, Walton Hall, Milton Keynes, UK
²Department of Earth Sciences, The Natural History Museum, London, UK
Published by arrangement with John Wiley & Sons

Carbon and nitrogen data from stepped combustion analysis of eight angrites, seven eucrites, and two diogenites, alongside literature data from a further nine eucrites and two diogenites, have been used to assess carbon and nitrogen incorporation and isotope fractionation processes on the angrite parent body (APB), for comparison with volatile behavior on the HED parent body (4 Vesta). A subset of the angrite data has been reported previously (Abernethy et al. 2013). Two separate families of volatile components were observed. They were (1) moderately volatile material (MVM), mostly combusting between ~500 and 750 °C and indistinguishable from terrestrial contamination and (2) refractory material (RM), mainly released above 750 °C and thought to be carbon (as math formula) and nitrogen (as N2 or math formula) dissolved within the silicate lattice, fitting with the slightly oxidized (~IW to IW+2) angrite fO2 conditions. Isotopic fractionation trends for carbon and nitrogen within the plutonic and basaltic (quenched) angrites suggest that the behavior of the two volatile elements is loosely coupled, but that the fractionation process differs between the two angrite subgroups. Comparison with results from eucrites and diogenites implies similarities between speciation of carbon and nitrogen on 4 Vesta and the APB, with the latter being more enriched in volatiles than the former.