¹Jeremy J. Kent,²Alan D. Brandon,³Katherine H. Joy,⁴Anne H. Peslier,²Thomas J. Lapen,⁵Anthony J. Irving,⁶Daniel M. Coleff
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12898]
¹GeoControl Systems, Jacobs J.E.T.S. Contract, NASA-Johnson Space Center, Houston, Texas, USA
²University of Houston, Department of Earth and Atmospheric Sciences, Houston, Texas, USA
³School of Earth and Environmental Sciences, University of Manchester, Manchester, UK
⁴Jacobs, NASA-Johnson Space Center, Houston, Texas, USA
⁵University of Washington, Department of Earth and Space Sciences, Seattle, Washington, USA
⁶HX5, Jacobs J.E.T.S. Contract, NASA-Johnson Space Center, Houston, Texas, USA
Published by arrangement with john Wiley & Sons

Lunar meteorite Northwest Africa (NWA) 5744 is a granulitic breccia with an anorthositic troctolite composition that may represent a distinct crustal lithology not previously described. This meteorite is the namesake and first-discovered stone of its pairing group. Bulk rock major element abundances show the greatest affinity to Mg-suite rocks, yet trace element abundances are more consistent with those of ferroan anorthosites. The relatively low abundances of incompatible trace elements (including K, P, Th, U, and rare earth elements) in NWA 5744 could indicate derivation from a highlands crustal lithology or mixture of lithologies that are distinct from the Procellarum KREEP terrane on the lunar nearside. Impact-related thermal and shock metamorphism of NWA 5744 was intense enough to recrystallize mafic minerals in the matrix, but not intense enough to chemically equilibrate the constituent minerals. Thus, we infer that NWA 5744 was likely metamorphosed near the lunar surface, either as a lithic component within an impact melt sheet or from impact-induced shock.

¹Alex M. Ruzicka,¹Melinda Hutson,^2,3Jon M. Friedrich,⁴Mark L. Rivers,^3,5Michael K. Weisberg,³Denton S. Ebel,⁶Karen Ziegler,⁷Douglas Rumble III,^2,8Alyssa A. Dolan
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12901]
¹Cascadia Meteorite Laboratory, Department of Geology, Portland State University, Portland, Oregon, USA
²Department of Chemistry, Fordham University, Bronx, New York, USA
³Department of Earth and Planetary Sciences, American Museum of Natural History, New York City, New York, USA
⁴Consortium for Advanced Radiation Sources, University of Chicago, Argonne, Illinois, USA
⁵Department of Physical Sciences, Kingsborough College and Graduate School of the City University of New York, Brooklyn, New York, USA
⁶Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico, USA
⁷Geophysical Laboratory, Carnegie Institution of Washington, Washington, D.C., USA
⁸Georgetown Law Center, Washington, D.C., USA
Published by arrangement with John Wiley & Sons

Miller Range 07273 is a chondritic melt breccia that contains clasts of equilibrated ordinary chondrite set in a fine-grained (<5 μm), largely crystalline, igneous matrix. Data indicate that MIL was derived from the H chondrite parent asteroid, although it has an oxygen isotope composition that approaches but falls outside of the established H group. MIL also is distinctive in having low porosity, cone-like shapes for coarse metal grains, unusual internal textures and compositions for coarse metal, a matrix composed chiefly of clinoenstatite and omphacitic pigeonite, and troilite veining most common in coarse olivine and orthopyroxene. These features can be explained by a model involving impact into a porous target that produced brief but intense heating at high pressure, a sudden pressure drop, and a slower drop in temperature. Olivine and orthopyroxene in chondrule clasts were the least melted and the most deformed, whereas matrix and troilite melted completely and crystallized to nearly strain-free minerals. Coarse metal was largely but incompletely liquefied, and matrix silicates formed by the breakdown during melting of albitic feldspar and some olivine to form pyroxene at high pressure (>3 GPa, possibly to ~15–19 GPa) and temperature (>1350 °C, possibly to ≥2000 °C). The higher pressures and temperatures would have involved back-reaction of high-pressure polymorphs to pyroxene and olivine upon cooling. Silicates outside of melt matrix have compositions that were relatively unchanged owing to brief heating duration.

¹L. J. Hicks, ¹J. L. Macarthur, ¹J. C. Bridges, ²M. C. Price, ²J. E. Wickham-Eade, ²M. J. Burchell, ¹G. M. Hansford, ³A. L. Butterworth, ¹S. J. Gurman, ¹S. H. Baker
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12909]
¹Department of Physics & Astronomy, Space Research Centre, University of Leicester, Leicester, UK
²School of Physical Sciences, University of Kent, Canterbury, UK
³Space Sciences Laboratory, University of California at Berkeley, Berkeley, California, USA
Published by arrangement with John Wiley & Sons

The mineralogy of comet 81P/Wild 2 particles, collected in aerogel by the Stardust mission, has been determined using synchrotron Fe-K X-ray absorption spectroscopy with in situ transmission XRD and X-ray fluorescence, plus complementary microRaman analyses. Our investigation focuses on the terminal grains of eight Stardust tracks: C2112,4,170,0,0; C2045,2,176,0,0; C2045,3,177,0,0; C2045,4,178,0,0; C2065,4,187,0,0; C2098,4,188,0,0; C2119,4,189,0,0; and C2119,5,190,0,0. Three terminal grains have been identified as near pure magnetite Fe3O4. The presence of magnetite shows affinities between the Wild 2 mineral assemblage and carbonaceous chondrites, and probably resulted from hydrothermal alteration of the coexisting FeNi and ferromagnesian silicates in the cometary parent body. In order to further explore this hypothesis, powdered material from a CR2 meteorite (NWA 10256) was shot into the aerogel at 6.1 km s−1, using a light-gas gun, and keystones were then prepared in the same way as the Stardust keystones. Using similar analysis techniques to the eight Stardust tracks, a CR2 magnetite terminal grain establishes the likelihood of preserving magnetite during capture in silica aerogel.

^1,2Valentin O. Osadchii, ³Mark V. Fedkin, ²Evgeniy G. Osadchii
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12919]
¹Department of Geochemistry, The Faculty of Geology, Moscow State University, Moscow, Russia
²Laboratory of High Temperature Electrochemistry, The Institute of ³Experimental Mineralogy, The Russian Academy of Science, Chernogolovka, Moscow Region, Russia
⁴Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, Pennyslvania, USA
Published by arrangement with John Wiley & Sons

High-temperature solid-state electrochemistry techniques (EMF method) were used to measure the oxygen fugacity (fO2) of the ordinary chondrites Ochansk (H4), Savtschenskoje (LL4), Elenovka (L5), Vengerovo (H5), and Kharkov (L6). The fO2 results are presented in the form of the following equations:

[not displayed here due to technical reasons]

It was found that fO2 regularly increases from H chondrites to LL chondrites. Measured fO2 are ~1.5 higher than those previously calculated from mineral assemblages. Kharkov (L6) is a little more oxidized than Elenovka (L5) in agreement with the progressive oxidation model. At the same time, Ochansk (H4) is more oxidized than Vengerovo (H5) and exhibits a slightly different slope compared to other chondrites and at T > 1200 K, becomes more reduced than Kharkov (L6) or Elenovka (L5). Measured oxygen fugacity values of meteorites fall within (0.1–1.0)·log fO2 of one another. The possible explanation of discrepancies between measured and calculated values is discussed.

^1,2,3Steven B. Simon, ^1,4Stephen R. Sutton
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12908]
¹Department of the Geophysical Sciences, The University of Chicago, Chicago, Illinois, USA
²The Field Museum of Natural History, Chicago, Illinois, USA
³Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico, USA
⁴Center for Advanced Radiation Sources (CARS), The University of Chicago, Chicago, Illinois, USA
Published by arrangement with John Wiley & Sons

The valences of Ti, V, and Cr in olivine and pyroxene, important indicators of the fO2 of the source region of their host rocks, can be readily measured nondestructively by XANES (X-ray absorption near edge structure) spectroscopy, but little such work has been done on lunar rocks, and there is some uncertainty regarding the presence of Ti3+ in lunar silicates and the redox state of the lunar mantle. This is the first study involving direct XANES measurement of valences of multivalent cations in lunar rocks. Because high alumina activity facilitates substitution of Ti cations into octahedral rather than tetrahedral sites in pyroxene and Ti3+ only enters octahedral sites, two aluminous basalts from Apollo 14, 14053 and 14072, were studied. Most pyroxene contains little or no detectable Ti3+, but in both samples relatively early, magnesian pyroxene was found that has Ti valences that are not within error of 4; in 14053, this component has an average Ti valence of 3.81 ± 0.06 (i.e., Ti3+/[Ti3+ + Ti4+ = 0.19]). This pyroxene has relatively low atomic Ti/Al ratios (<0.4) due to crystallization before plagioclase, contrary to the long-held belief that lunar pyroxene with Ti/Al > 0.5 contains Ti3+ and pyroxene with lower ratios does not. Later pyroxene, with lower Mg/Fe and higher Ti/Al ratios, has higher proportions of Ti (all Ti4+) in tetrahedral sites. All pyroxene analyzed contains divalent Cr, ranging from 15 to 30% of the Cr present, and all but one analysis spot contains divalent V, accounting for 0 to 40% (typically 20–30%) of the V present. Three analyses of olivine in 14053 do not show any Ti3+, but Ti valences in 14072 olivine range from 4 down to 3.70 ± 0.10. In 14053 olivine, ~50% of the Cr and 60% of the V are divalent. In 14072 olivine, the divalent percentages are ~20% for Cr and 20–60% for V. These results indicate significant proportions of divalent Cr and V and limited amounts of trivalent Ti in the parental melts, especially when crystal/liquid partitioning preferences are taken into account. These features are consistent with an fO2 closer to IW − 2 than to IW − 1. Apollo 15 basalt 15555, analyzed for comparison with A-14 materials, has olivine with strongly reduced Cr (Cr2+/(Cr2+ + Cr3+) ~0.9). Basalts from different sites may record redox differences between source regions.

¹Naotaka Tomioka,²Masaaki Miyahara
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12902]
¹Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Nankoku, Kochi, Japan
²Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Hiroshima, Japan
Published by arrangement with John Wiley & Sons

Heavily shocked meteorites contain various types of high-pressure polymorphs of major minerals (olivine, pyroxene, feldspar, and quartz) and accessory minerals (chromite and Ca phosphate). These high-pressure minerals are micron to submicron sized and occur within and in the vicinity of shock-induced melt veins and melt pockets in chondrites and lunar, howardite–eucrite–diogenite (HED), and Martian meteorites. Their occurrence suggests two types of formation mechanisms (1) solid-state high-pressure transformation of the host-rock minerals into monomineralic polycrystalline aggregates, and (2) crystallization of chondritic or monomineralic melts under high pressure. Based on experimentally determined phase relations, their formation pressures are limited to the pressure range up to ~25 GPa. Textural, crystallographic, and chemical characteristics of high-pressure minerals provide clues about the impact events of meteorite parent bodies, including their size and mutual collision velocities and about the mineralogy of deep planetary interiors. The aim of this article is to review and summarize the findings on natural high-pressure minerals in shocked meteorites that have been reported over the past 50 years.

¹Run-Lian Pang,^1,2Ai-Cheng Zhang,¹Ru-Cheng Wang
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12920]
¹State Key Laboratory for Mineral Deposits Research, School of Earth Science and Engineering, Nanjing University, Nanjing, China
²Lunar and Planetary Science Institute, Nanjing University, Nanjing, China
Published by agreement with John Wiley & Sons

We report on the petrography and mineralogy of three types of silicate veinlets in the brecciated eucrite Northwest Africa (NWA) 1109. These include Fe-rich olivine, Mg-rich olivine, and pyroxene veinlets. The Fe-rich olivine veinlets mainly infill fractures in pyroxene and also occur along grain boundaries between pyroxene and plagioclase crystals, in both nonequilibrated and equilibrated lithic clasts. The host pyroxene of Fe-rich olivine veinlets shows large chemical variations between and within grains. The Fe-rich olivine veinlets also contain fine-grained Fe3+-bearing chromite, highly calcic plagioclase, merrillite, apatite, and troilite. Based on texture and mineral chemistry, we argue that the formation of Fe-rich olivine was related to fluid deposition at relatively high temperatures. However, the source of Fe-rich olivine in the veinlets remains unclear. Magnesium-rich olivine veinlets were found in three diogenitic lithic clasts. In one of these, the Mg-rich olivine veinlets only occur in one of the fine-grained interstitial regions and extend into fractures within surrounding coarse-grained orthopyroxene. Based on the texture of the interstitial materials, we suggest that the Mg-rich olivine veinlets formed by shock-induced localized melting and recrystallization. Pyroxene veinlets were only observed in one clast where they infill fractures within large plagioclase grains and are associated with fine-grained pyroxene surrounding coarse-grained pyroxene. The large chemical variations in pyroxene and the fracture-filling texture indicate that the pyroxene veinlets might also have formed by shock-induced localized melting and rapid crystallization. Our study demonstrates that silicate veinlets formed by a range of different surface processes on the surface of Vesta.

^1,2Arshad Ali,¹Sobhi J. Nasir,²Iffat Jabeen,³Ahmed Al Rawas,²Neil R. Banerjee,
^2,4Gordon R. Osinski
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12903]
¹Earth Sciences Research Centre, Sultan Qaboos University, Muscat 123, Sultanate of Oman
²Department of Earth Sciences & Centre for Planetary Science and Exploration, Western University, London, Ontario, Canada
³Department of Physics, College of Science, Sultan Qaboos University, Muscat 123, Sultanate of Oman
⁴Department of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada
Published by arrangement with John Wiley & Sons

Dhofar 1671 is a relatively new meteorite that previous studies suggest belongs to the Rumuruti chondrite class. Major and REE compositions are generally in agreement with average values of the R chondrites (RCs). Moderately volatile elements such as Se and Zn abundances are lower than the R chondrite values that are similar to those in ordinary chondrites (OCs). Porphyritic olivine pyroxene (POP), radial pyroxene (RP), and barred olivine (BO) chondrules are embedded in a proportionately equal volume of matrix, one of the characteristic features of RCs. Microprobe analyses demonstrate compositional zoning in chondrule and matrix olivines showing Fa-poor interior and Fa-rich outer zones. Precise oxygen isotope data for chondrules and matrix obtained by laser-assisted fluorination show a genetic isotopic relationship between OCs and RCs. On the basis of our data, we propose a strong affinity between these groups and suggest that OC chondrule precursors could have interacted with a 17O-rich matrix to form RC chondrules (i.e., ∆17O shifts from ~1‰ to ~3‰). These interactions could have occurred at the same time as “exotic” clasts in brecciated samples formed such as NWA 10214 (LL3–6), Parnallee (LL3), PCA91241 (R3.8–6), and Dhofar 1671 (R3.6). We also infer that the source of the oxidation and 17O enrichment is the matrix, which may have been enriched in 17O-rich water. The abundance of matrix in RCs relative to OCs, ensured that these rocks would be apparently more oxidized and appreciably 17O-enriched. In situ analysis of Dhofar 1671 is recommended to further strengthen the link between OCs and RCs.

¹Chi Ma, ²Alexander N. Krot, ²Kazuhide Nagashima
American Mineralogist 102, 1556-1560 Link to Article [https://doi.org/10.2138/am-2017-6032]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.
²Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i 96822, U.S.A.
Copyright: The Mineralogical Society of America

Addibischoffite (IMA 2015-006), Ca2Al6Al6O20, is a new calcium aluminate mineral that occurs with hibonite, perovskite, kushiroite, Ti-kushiroite, spinel, melilite, anorthite, and FeNi-metal in the core of a Ca-Al-rich inclusion (CAI) in the Acfer 214 CH3 carbonaceous chondrite. The mean chemical composition of type addibischoffite measured by electron probe microanalysis is (wt%) Al2O3 44.63, CaO 15.36, SiO2 14.62, V2O3 10.64, MgO 9.13, Ti2O3 4.70, FeO 0.46, total 99.55, giving rise to an empirical formula of (Ca2.00)(Al2.55Mg1.73V1.3+08Ti3+0.50Ca0.09Fe2+0.05)∑6.01(Al4.14Si1.86)O20. The general formula is Ca2(Al,Mg,V,Ti)6(Al,Si)6O20. The end-member formula is Ca2Al6Al6O20. Addibischoffite has the P1̄ aenigmatite structure with a = 10.367 Å, b = 10.756 Å, c = 8.895 Å, α = 106.0°, β = 96.0°, γ = 124.7°, V = 739.7 Å3, and Z = 2, as revealed by electron backscatter diffraction. The calculated density using the measured composition is 3.41 g/cm3. Addibischoffite is a new member of the warkite (Ca2Sc6Al6O20) group and a new refractory phase formed in the solar nebula, most likely as a result of crystallization from an 16O-rich Ca, Al-rich melt under high-temperature (~1575 °C) and low-pressure (~10−4 to 10−5 bar) conditions in the CAI-forming region near the protosun, providing a new puzzle piece toward understanding the details of nebular processes. The name is in honor of Addi Bischoff, cosmochemist at University of Münster, Germany, for his many contributions to research on mineralogy of carbonaceous chondrites, including CAIs in CH chondrites.

¹Kent C. Condie, ²Charles K. Shearer
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.06.034]
¹Department of Earth and Environmental Science, New Mexico Tech, Socorro, NM 87801, USA
²Institute of Meteoritics, University of New Mexico, Albuquerque, NM 87131, USA
Copyright Elsevier

The distribution of high field strength incompatible element ratios Zr/Nb, Nb/Th, Th/Yb and Nb/Yb in terrestrial oceanic basalts prior to 2.7 Ga suggests the absence or near-absence of an enriched mantle reservoir. Instead, most oceanic basalts reflect a variably depleted mantle source similar in composition to primitive mantle. In contrast, basalts from hydrated mantle sources (like those associated with subduction) exist from 4 Ga onwards. The gradual appearance of enriched mantle between 2 and 3 Ga may reflect the onset and propagation of plate tectonics around the globe. Prior to 3 Ga, Earth may have been in a stagnant-lid regime with most basaltic magmas coming from a rather uniform, variably depleted mantle source or from a non-subduction hydrated mantle source. It was not until the extraction of continental crust and accompanying propagation of plate tectonics that “modern type” enriched and depleted mantle reservoirs developed. Consistent with the absence of plate tectonics on the Moon is the near absence of basalts derived from depleted (DM) and enriched (EM) mantle reservoirs as defined by the four incompatible element ratios of this study. An exception are Apollo 17 basalts, which may come from a mixed source with a composition similar to primitive mantle as one end member and a high-Nb component as the other end member. With exception of Th, which requires selective enrichment in at least parts of the martian mantle, most martian meteorites can be derived from sources similar to terrestrial primitive mantle or by mixing of enriched and depleted mantle end members produced during magma ocean crystallization. Earth, Mars and the Moon exhibit three very different planetary evolution paths. The mantle source regions for Mars and the Moon are ancient and have HFS element signatures of magma ocean crystallization well-preserved, and differences in these signatures reflect magma ocean crystallization under two distinct pressure regimes. In contrast, plate tectonics on Earth has destroyed most or all of the magma ocean crystallization geochemical record, or less likely, the terrestrial magma ocean may not have been strongly fractionated during crystallization. The rather uniform incompatible element ratio record in pre-2 Ga oceanic terrestrial basalts requires vigorous mixing of most of the mantle between magma ocean crystallization and about 4 Ga, the onset of the preserved greenstone record.