Composition and origin of the volatile components released from the Pesyanoe aubrite by stepwise crushing and heating

Geochemistry [Chemie der Erde] (in Press) Link to Article []
1Vernadsky Institute of Geochemistry and Analytical chemistry RAS, Kosygin St. 19, 119999, Moscow, Russia
2A. N. Frumkin Institute of physical chemistry and electrochemistry RAS, Leninsky pr. 31 korp. 4, Moscow, 119071, Russia
3Institute of geology of ore deposits, Petrography, Mineralogy, and Geochemistry RAS, Staromonetnyi per, 35, 119017 Moscow, Russia
Copyright Elsevier

Aubrites are achondritic meteorites (enstatite pyroxenites) that were formed in highly reduced magmatic environments on a differentiated parent body sharing a common oxygen isotope reservoir with enstatite chondrites (EC), Earth and Moon, and could be considered as a geochemical model of the early proto-Earth. Some pyroxenes of the Pesyanoe aubrite have high abundance of gaseous inclusions, captured during the crystallization of the rocks. Investigation of the inclusions by IR spectroscopy reveals presence of OH− groups and C–H bonds. The former are assigned to protonated point defects in enstatite lattice and the latter to compounds occupying void walls. Molecular water and CO2 were not observed. Volatile components released from the samples of the Pesyanoe enstatite by stepwise crushing and heating are composed of CO2, H2O and a non-condensable phase. Hydrogen isotopic composition of volatiles extracted in form of molecular water in Px-separates varies in the range δD = −61 – −84‰ with mean value of δD = −73 ± 16‰ VSMOW and is within the ranges of ECs and Earth’s mantle. The total abundance of H2 in the pyroxene of Pesyanoe were estimated as at least 0.024 ppm that is too low in comparison with that of enstatite chondrites (≥30 ppm H2) and could indicate nearly complete degassing of the Pesyanoe primitive precursor material during the Pesyanoe parent body accretion or a mantle degassing in igneous differentiation process. In a last case a primitive precursor could have D/H ratio different from that of enstatite chondrites.

Ages of lunar impact breccias: Limits for timing of the Imbrium impact

1,2Alexander A. Nemchin et al. (>10)
Geochemistry [Chemie der Erde] (in Press) Link to Article []
1Institute of Geology, Chinese Academy of Geological Sciences, Beijing, China
2School of Earth and Planetary Sciences, Curtin University, Perth, GPO Box U1987, WA, 6845, Australia
Copyright Elsevier

Since the Apollo 14 mission delivered samples of the Fra Mauro formation, interpreted as ejecta of the Imbrium impact, defining the age of this impact has emerged as one of the critical tasks required for the complete understanding of the asteroid bombardment history of the Moon and, by extension, the inner Solar System. Significant effort dedicated to this task has resulted in a substantial set of ages centered around 3.9 Ga and obtained for the samples from most Apollo landing sites using a variety of chronological methods. However, the available age data are scattered over a range of a few tens of millions of years, which hinders the ability to distinguish between the samples that are truly representative of the Imbrium impact and those formed/reset by other, broadly contemporaneous impact events. This study presents a new set of U-Pb ages obtained for the VHK (very high K) basalt clasts found in the Apollo 14 breccia sample 14305 and phosphates from (i) several fragments of impact-melt breccia extracted from Apollo 14 soil sample 14161, and (ii) two Apollo 15 breccias 15455 and 15445. The new data obtained for the Apollo 14 samples increase the number of independently dated samples from this landing site to ten. These Apollo 14 samples represent the Fra Mauro formation, which is traditionally viewed as Imbrium ejecta, and therefore should record the age of the Imbrium impact. Using the variance of ten ages, we propose an age of 3922 ± 12 Ma for this event. Samples that yield ages within these limits can be considered as possible products of the Imbrium impact, while those that fall significantly outside this range should be treated as representing different impact events. Comparison of this age for Imbrium (determined from Apollo 14 samples) with the ages of another eleven impact-melt breccia samples collected at four other landing sites and a related lunar meteorite suggests that they can be viewed as part of Imbrium ejecta. Comprehensive review of 40Ar/39Ar ages available for impact melt samples from different landing sites and obtained using the step-heating technique, suggests that the majority of the samples that gave robust plateau ages are indistinguishable within uncertainties and altogether yield a weighted average age of 3916 ± 7 Ma (95 % conf., MSWD = 1.1; P = 0.13) and a median average age of 3919 + 14/-12 Ma, both of which agree with the confidence interval obtained using the U-Pb system. These samples, dated by 40Ar/39Ar method, can be also viewed as representing the Imbrium impact. In total 36 out of 41 breccia samples from five landing sites can be interpreted to represent formation of the Imbrium basin, supporting the conclusion that Imbrium material was distributed widely across the near side of the Moon. Establishing temporal limits for the Imbrium impact allows discrimination of ten samples with Rb-Sr and 40Ar/39Ar ages about 50 Ma younger than 3922 ± 12 Ma. This group may represent a separate single impact on the Moon and needs to be investigated further to improve our understanding of lunar impact history.

The lunar surface as a recorder of astrophysical processes

1,2Ian A. Crawford,3Katherine H. Joy,1Jan H. Pasckert,1Harald Hiesinger
Philosophical Transactions of the Royal Society A 379, 2188. Link to Article []
1Department of Earth and Planetary Sciences, Birkbeck College, University of London, Malet Street, London WC1E 7HX, UK
2Centre for Planetary Sciences at UCL/Birkbeck, Gower Street, London WC1E 6BT, UK
3Department of Earth and Environmental Sciences, The University of Manchester, Oxford Road, M13 9PL Manchester, UK
4Institut für Planetologie, Westfälische Wilhelms-Universität, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany

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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.