The origins and oxygen isotopes in two Al-rich chondrules from Kainsaz CO3 carbonaceous chondrites.

1Dai, D.,1,2Bao, H.,1,2Liu, S.,1,3Yin, F.
Yanshi Xuebao/Acta Petrologica Sinica 36, 1850-1856 Link to Article [DOI: 10.18654/1000-0569/2020.06.13]
1Institute of Geology, Hunan University of Science and Technology, Xiangtan, 411201, China
2Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081, China
3Hunan Provincial Key Laboratory of Shale Gas Resource Utilization, Xiangtan, 411201, China

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Isotopic Composition of Noble Gases, Nitrogen, and Carbon in the Ozerki New L Chondrite

1Korochantseva, E.V.,2Verchovsky, A.B.,1Buikin, A.I.,1Lorents, K.A.,1Korochantsev, A.V.
Geochemistry International 58, 1239-1256 Link to Article [DOI: 10.1134/S0016702920110075]
1Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, 119991, Russian Federation
2The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom

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Quartz and cristobalite ballen in impact melt rocks from the Ries impact structure, Germany, formed by dehydration of shock‐generated amorphous phases

1Claudia A. Trepmann,1Fabian Dellefant,2Melanie Kaliwoda,1Kai‐Uwe Hess,1,2Wolfgang W. Schmahl,3Stefan Hölzl
Meteoritics & Planetary Science (in Press) Link to Article []
1Department of Earth and Environmental Sciences, Ludwig‐Maximilians‐University, 80333 Munich, Germany
2Mineralogische Staatssammlung, Staatliche naturwissenschaftliche Sammlungen Bayerns, 80333 Munich, Germany
3RiesKraterMuseum, Staatliche naturwissenschaftliche Sammlungen Bayerns, 86720 Nördlingen, Germany
Published by arrangement with John Wiley & Sons

Quartz and cristobalite ballen aggregates surrounded by dendritic cristobalite in gneiss clasts of impact melt rocks from the Ries impact structure are analyzed by Raman spectroscopy, microscopy, and electron backscattered diffraction to elucidate the development of the characteristic polycrystalline ballen that are defined by curved interfaces between each other. We suggest that the investigated ballen aggregates represent former fluid inclusion‐rich quartz grains from the granitic gneiss protolith. Upon shock loading, they transformed into an amorphous phase that partly retained information on the precursor structure. Volatiles from inclusions dissolved into the amorphous phase. During decompression and cooling, dehydration takes place and causes fracturing of the amorphous phase and disintegration into small globular ballen, with the fluid being expelled along the fractures. A similar formation of small globules due to dehydration of silica‐rich glass is known for perlitic structures of volcanic rocks. Remnants of the precursor structure are present in the amorphous phase and enabled topotactic crystallization of quartz, leading to a crystallographic preferred orientation. Crystallization of more distorted parts of the amorphous phase led to random orientations of the quartz crystals. Ballen comprised of cristobalite formed from a dehydrated amorphous phase with no structural memory of the precursor. Dendritic cristobalite exclusively occurring at the rim of quartz ballen aggregate is interpreted to have crystallized directly from a melt enriched in fluids that were expelled during dehydration of the amorphous phase.

Evidence for the presence of chondrule‐ and CAI‐derived material in an isotopically anomalous Antarctic micrometeorite

1,2Bastien Soens,3,4Martin D. Suttle,1Ryoga Maeda,5Frank Vanhaecke,6Akira Yamaguchi,7Matthias Van Ginneken,2Vinciane Debaille,1Philippe Claeys,1Steven Goderis
Meteoritics & Planetary Science (in Press) Link to Article []
1Analytical‐, Environmental‐, and Geo‐Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, Brussels, 1050 Belgium
2Laboratoire G‐Time, Université Libre de Bruxelles 50, Av. F.D. Roosevelt CP 160/02, Brussels, 1050 Belgium
3Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, Pisa, 56126 Italy
4Planetary Materials Group, Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD UK
5Atomic & Mass Spectrometry – A&MS Research Group, Department of Chemistry, Ghent University, Krijgslaan 218 – S12, Ghent, 9000 Belgium
6National Institute of Polar Research, 10‐3 Midori‐cho, Tachikawa‐shi, Tokyo, 190‐8518 Japan
7Centre for Astrophysics and Planetary Science, University of Kent, Canterbury, Kent, CT2 7NZ UK
Published by arrangement with John Wiley & Sons

We report the discovery of a unique, refractory phase‐bearing micrometeorite (WF1202A‐001) from the Sør Rondane Mountains, East Antarctica. A silicate‐rich cosmic spherule (~400 µm) displays a microporphyritic texture containing Ca‐Al‐rich inclusion (CAI)‐derived material (~5–10 area%), including high‐Mg forsterite (Fo98‐99) and enstatite (En98‐99, Wo0‐1). The micrometeorite also hosts a spherical inclusion (~209 µm), reminiscent of chondrules, displaying a barred olivine texture. Oxygen isotopic compositions of the micrometeorite groundmass (δ17O = –3.46‰, δ18O = 10.43‰, ∆17O = –1.96‰) are consistent with a carbonaceous chondrite precursor body. Yet, a relict forsterite grain is characterized by δ17O = –45.8‰, δ18O = –43.7‰, ∆17O = –23.1‰, compatible with CAIs. In contrast, a relict low‐Ca pyroxene grain (δ17O = –4.96‰, δ18O = –4.32‰, ∆17O = –2.71‰) presumably represents a first‐generation silicate grain that accreted 18O‐rich gas or dust in a transient melting scenario. The spherical inclusion displays anomalous oxygen isotope ratios (δ17O = –0.98‰, δ18O = –2.16‰, ∆17O = 0.15‰), comparable to anhydrous interplanetary dust particles (IDPs) and fragments from Comet 81P/Wild2. Based on its major element geochemistry, the chondrule size, and oxygen isotope systematics, micrometeorite WF1202A‐001 likely sampled a carbonaceous chondrite parent body similar to, but distinct from CM, CO, or CV chondrites. This observation may suggest that some carbonaceous chondrite bodies can be linked to comets. The reconstructed atmospheric entry parameters of micrometeorite WF1202A‐001 suggest that the precursor particle originated from a low‐inclination, low‐eccentricity source region, most likely either the main belt asteroids or Jupiter family comets (JFCs).

Ages and chemistry of mare basaltic units in the Grimaldi basin on the nearside of the Moon: Implications for the volcanic history of the basin

1P. M. Thesniya,1V. J. Rajesh,2J. Flahaut
Meteoritics & Planetary Science (in Press) Link to Artuicle []
1Department of Earth and Space Sciences, Indian Institute of Space Science and Technology, Valiamala (P. O.), Thiruvananthapuram, 695547 India
2Centre de Recherches Pétrographiques et Géochimiques (CRPG)—CNRS/Université de Lorraine, 15 rue Notre Dame des Pauvres, 54500 Vandoeuvre les Nancy, France
Published by arrangement with John Wiley & Sons

Lunar mare basalts represent flood volcanism between ~4.0 and 1.2 Ga, therefore, providing insights into the thermal and volcanic history of the Moon. The present study investigates the spectral and chemical characteristics as well as ages of the nearside mare basaltic units from the Grimaldi basin, namely Mare Grimaldi and Mare Riccioli, using a wealth of orbital remote sensing data. This study delineated distinct basaltic units of varying albedo, mineralogy, and titanium contents in both Mare Grimaldi and Mare Riccioli. The crater size–frequency distribution technique revealed that at least two phases of basaltic magmatism spanning ~3.5 to 1.5 Ga (Late Imbrian‐Eratosthenian) have occurred in the Grimaldi basin. High‐Ti olivine basalts dated at 2.05 Ga are found to be surrounded by the Late Imbrian (~3.47 Ga) low‐ to intermediate‐Ti basalts in Mare Grimaldi. Low‐ to intermediate‐Ti basalts observed in Mare Riccioli date back to two different volcanic events at ~3.5 Ga and ~3.2 billion years, while patches of basalts having remarkably higher titanium content within the Mare Riccioli record the youngest age of ~1.5 Ga. The chemical trend of the pyroxenes from distinct basaltic units also revealed that multiple events of volcanism have occurred in the Grimaldi basin. The high‐Ti basalts in the Mare Grimaldi crystallized from an Fe‐enriched late‐stage magma while the low‐Ti basalts crystallized from an Mg‐ and Ca‐rich initial magma that experienced an ultra‐late stage quenching. The low‐ to intermediate‐Ti basaltic magma erupted in both the units was derived by partial melting of early cumulate materials from the hybrid source region in the post‐overturn upper mantle and made its way to the surface through dikes that propagated by excess pressures accumulated in the diapirs stalled at the base of the crust due to buoyancy trap. The high‐Ti magma erupted in the Mare Grimaldi was generated by a hot plume ascended from deeper clinopyroxene–ilmenite‐rich cumulate layer near the core–mantle boundary. However, the Eratosthenian (~1.5 Ga) intermediate‐Ti volcanic activity in the Mare Riccioli rather sourced from the ilmenite–clinopyroxene cumulate materials thet remained in the upper mantle after mantle overturn. The new results suggest that volcanism had not ceased in the Grimaldi basin at 3.27 Ga, rather it was active and fed by different mantle sources until 1.5 Ga for a period spanning ~2 billion years.

Biconical reflectance, micro‐Raman, and nano‐FTIR spectroscopy of the Didim (H3‐5) meteorite: Chemical content and molecular variations

1M. Yesiltas,2M. Kaya,3T. D. Glotch,4R. Brunetto,5A. Maturilli,5J. Helbert,6M. E. Ozel
Meteoritics & Planetary Science (in Press) Link to Article []
1Faculty of Aeronautics and Space Sciences, Kirklareli University, Kirklareli, 39100 Turkey
2Institute of Acceleration Technologies, Ankara University, Ankara, 06830 Turkey
3Department of Geosciences, Stony Brook University, Stony Brook, New York, 11794 USA
4Université Paris‐Saclay, CNRS, Institut d’Astrophysique Spatiale, 91405 Orsay, France
5DLR, Berlin, Germany
6Space Sciences and Solar Energy Research and Application Center, Cukurova University, Adana, 01380 Turkey
Published by arrangement with John Wiley & Sons

The Didim meteorite contains multiple lithologies and clasts of different petrologic types in a single stone. A mixture of H5 clasts in an unequilibrated H3 host was previously observed in Didim, according to the initial characterization reported in the Meteoritical Bulletin Database, providing an opportunity to investigate molecular composition that contains varying degree of equilibrium with varying mineralogy. We have taken a “from large scale to small scale” approach to spectroscopically investigate the chemical content of Didim. Centimeter‐scale biconical reflectance spectra show that Didim contains abundant olivine, pyroxene, and other optically active minerals, evident from a strong Band I near 0.93 µm and a weak Band II near 1.75 µm. Micrometer‐scale Raman spectroscopic investigations reveal the presence of carbonaceous material in addition to forsteritic olivine, pyroxene (augite and enstatite), feldspars, and opaque phases such as chromite and hematite. 3‐D Raman tomographic imaging shows that the carbonaceous material near chondrules extends underneath a large olivine grain, going further down toward the interior, indicating that the observed carbonaceous matter is likely indigenous. Nano‐scale infrared measurements reveal that the observed chemical materials in Didim contain spectral, and therefore, molecular, variations at the ~20 nm spatial scale. These chemical variations are normally not accessible via conventional infrared techniques, and indicate the presence of different cations in the molecular composition of observed minerals. By taking the “large scale to small scale” approach, we show that these compositional variations can be captured and investigated nondestructively in meteorites to understand formation/evolution of chemical components in the parent body.

Early solar system aqueous activity: K isotope evidence from Allende

1,2Yun Jiang,3Piers Koefoed,3Olga Pravdivtseva,3,4Heng Chen,2,5Chun‐Hui Li,2,5Fang Huang,2,5Li‐Ping Qin,2,5Jia Liu,3Kun Wang
Meteoritics & Planetary Science (in Press) Link to Article []
1CAS Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, 210008 China
2CAS Center for Excellence in Comparative Planetology, Hefei, China
3Department of Earth and Planetary Sciences, McDonnell Center for the Space Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, Missouri, 63130 USA
4Lamont‐Doherty Earth Observatory, Columbia University, Palisades, New York, 10964 USA
5CAS Key Laboratory of Crust‐Mantle Materials and Environments, School of Earth and Space Sciences,
University of Science and Technology of China, Hefei, Anhui, 230026 China
Published by arrangement with John Wiley & Sons

The alkali element K is moderately volatile and fluid mobile; thus, it can be influenced by both primary processes (evaporation and recondensation) in the solar nebula and secondary processes (thermal and aqueous alteration) in the parent body. Since these primary and secondary processes would induce different isotopic fractionations, K isotopes could become a potential tracer to distinguish them. Using recently developed methods with improved precision (0.05‰, 95% confidence interval), we systematically measured the K isotopic compositions and major/trace elemental compositions of chondritic components (18 chondrules, 3 CAIs, 2 matrices, and 5 bulks) in the carbonaceous chondrite fall Allende. Among all the components analyzed in this study, CAIs, which formed initially under high‐temperature conditions in the solar nebula and were dominated by nominally K‐free refractory minerals, have the highest K2O content (average 0.53 wt%) and have K isotope compositions most enriched in heavy isotopes (δ41K: −0.30 to −0.25‰). Such an observation is consistent with previous petrologic studies that show CAIs in Allende have undergone alkali enrichment during metasomatism. In contrast, chondrules contain lower K2O content (0.003–0.17 wt%) and generally lighter K isotope compositions (δ41K: −0.87‰ to −0.24‰). The matrix and bulks are nearly identical in K2O content and K isotope compositions (0.02–0.05 wt%; δ41K: −0.62 to − 0.46‰), which are, as expected, right in the middle of CAIs and chondrules. This strongly indicates that most of the chondritic components of Allende suffered aqueous alteration and their K isotopic compositions are the ramification of Allende parent‐body processing instead of primary nebular signatures. Nevertheless, we propose the small K isotope fractionations observed (< 1‰) among Allende components are likely similar to the overall range of K isotopic fractionation that occurred in nebular environment. Furthermore, the K isotope compositions seen in the components of Allende in this study are consistent with MC‐ICP‐MS analyses of the components in ordinary chondrites, which also show an absence of large (10‰) isotope fractionations. This is not expected as evaporation experiments in nebular conditions suggest there should be large K isotopic fractionations. Nevertheless, possible nebular processes such as chondrules back exchanging with ambient gas when they formed could explain this lack of large K isotopic variation.

The role of hydrothermal sulfate reduction in the sulfur cycles within Europa: Laboratory experiments on sulfate reduction at 100 MPa

1,2Shuya Tan,1,3Yasuhito Sekine,4Takazo Shibuya,2Chihiro Miyamoto,2Yoshio Takahashi
Icarus (in Press) Link to Article []
1Earth-Life Science Institute (ELSI), Tokyo Institute of Technology, Tokyo, Japan
2Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan
3Institute of Nature and Environmental Technology, Kanazawa University, Kanazawa, Japan
4Super-cutting-edge Grand and Advanced Research (SUGAR) Program, Institute for Extra-cutting-edge Science and Technology Avant-garde Research (X-star), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan
Copyright Elsevier

There are several lines of evidence for the subsurface ocean within Europa; however, its oceanic chemistry and geochemical cycles are largely unknown. The recent observations by large telescopes show that exogenic sulfur ions and SO2 are implanted from Io and accumulate as sulfuric acids in Europa’s trailing hemisphere. This suggests that a large amount of sulfate could have been supplied into the ocean over geological timescales. The telescope observations also suggest that chloride salts appear on chaotic terrains of Europa, suggesting that the primary oceanic anion may be chloride despite a supply of sulfate into the ocean. These observations imply the presence of possible sinks of exogenic sulfate within the ocean. Here, we report the results of laboratory experiments on hydrothermal sulfate reduction under the pressure conditions that correspond to Europa’s seafloor. Using a Dickson-type experimental system, we obtain the reaction rate of sulfate reduction at a pressure of 100 MPa and temperature of 280 °C for various pH levels (pH 2–7). We find strong pH dependence and little pressure dependence of the reaction rate. Sulfate reduction proceeds effectively at fluid pH < 6, whereas it is kinetically inhibited at fluid pH ~7. These results suggest that, if hydrothermal fluid pH is <6, hydrothermal sulfate reduction within Europa can be a sink of exogenic sulfate within the ocean in addition to precipitation of sulfate salts. Such acidic fluid pH may be achieved if hydrothermal activity is hosted by basaltic rocks. We suggest the importance of the thermal evolution of the rocky interior for both the ocean chemistry and sulfur cycles of Europa.

Thickness of orthopyroxene-rich materials of ejecta deposits from the south pole-Aitken basin

1,2Xunyu Zhang,3Minggang Xie,4,1,2,5Zhiyong Xiao
Icarus (in Press) Link to Article []
1State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau, PR China
2CNSA Macau Center for Space Exploration and Science, Macau, PR China
3College of Science, Guilin University of Technology, Guilin 541006, PR China
4School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai 519082, PR China
5CAS Center for Excellence in Comparative Planetology, Hefei 230026, PR China
Copyright Elsevier

The South Pole-Aitken (SPA) basin is the largest impact structure on the Moon and is believed to have excavated the orthopyroxene (Opx)-rich lower crust and/or upper mantle materials. For the complex craters outside of the SPA transient cavity, the origin of the Opx-rich central peaks is possibly from either the Opx-rich materials of the SPA ejecta deposits or the unexcavated lower crust and/or upper mantle. To estimate the thickness of the Opx-rich materials of the SPA ejecta deposits, this study investigated large complex craters (dozens of kilometers) that have penetrated the Opx-rich materials and exposed deeper mafic-poor crustal material based on spectra extracted from small fresh craters (sub-kilometer scale). The amount of foreign material introduced to these large complex craters by other lunar impact events was estimated to guarantee the least influence on the compositional analysis. The study results suggest that a 56 km-diameter crater at ~640 km northwest of the SPA center is large enough to penetrate the Opx-rich materials of the SPA ejecta deposits, which are thinner than ~4.7 km at this location. This result also indicates that the intense bombardment history of the large craters and basins outside of the SPA transient cavity excavated and redistributed a large amount of crustal material across the basin, possibly resulting in the heterogeneous distribution of mafic-rich and mafic-poor materials on the SPA surface.