In-situ U-Pb dating of Ries Crater lacustrine carbonates (Miocene, South-West Germany): Implications for continental carbonate chronostratigraphy

1,2,3,4Damaris Montano,1,5Marta Gasparrini,2,3Axel Gerdes,5Giovanna Della Porta,2,3Richard Albert
Earth and Planetary Science Letters 568, 117011 Link to Article [https://doi.org/10.1016/j.epsl.2021.117011]
1IFP Energies nouvelles, 1-4 avenue de Bois-Préau, 92852, Rueil-Malmaison, France
2Institut für Geowissenschaften, Goethe University Frankfurt, Altenhöferallee 1, 60438 Frankfurt am Main, Germany
3Frankfurt Isotope and Element Research Center (FIERCE), Goethe University Frankfurt, Frankfurt am Main, Germany
4Sorbonne Université; ED 398 – GRNE, 4, place Jussieu, 75252 Paris, France
5Università degli Studi di Milano; Dipartimento di Scienze della Terra “Ardito Desio”, via Mangiagalli 34, 20133 Milan, Italy
Copyright Elsevier

The Nördlinger Ries Crater lacustrine basin (South-West Germany), formed by a meteorite impact in the Miocene (Langhian; ∼14.9 Ma), offers a well-established geological framework to understand the strengths and limitations of U-Pb LA-ICPMS (in situ Laser Ablation-Inductively Coupled Plasma Mass Spectrometry) geochronology as chronostratigraphic tool for lacustrine (and more broadly continental) carbonates. The post-impact deposits include siliciclastic basinal facies at the lake centre and carbonate facies at the lake margins, coevally deposited in a time window of >1.2 and <2 Ma. Depositional and diagenetic carbonate phases (micrites and calcite cements) were investigated from three marginal carbonate facies (Hainsfarth bioherm, Adlersberg bioherm and Wallerstein mound). Petrography combined with C and O stable isotope analyses indicate that most depositional and early diagenetic carbonates preserved pristine geochemical compositions and thus the U-Pb system should reflect the timing of original precipitation. In total, 22 U-Pb ages were obtained on 10 different carbonate phases from five samples. The reproducibility and accuracy of the U-Pb (LA-ICPMS) method were estimated to be down to 1.5% based on repeated analyses of a secondary standard (speleothem calcite ASH-15d) and propagated to the obtained ages. Micrites from the Hainsfarth, Adlersberg and Wallerstein facies yielded ages of 13.90 ± 0.25, 14.14 ± 0.20 and 14.33 ± 0.27 Ma, respectively, which overlap within uncertainties, and are consistent with the weighted average age of 14.30 ± 0.20 Ma obtained from all the preserved depositional and early diagenetic phases. Data indicate that sedimentation started shortly after the impact and persisted for >1.2 and <2 Ma, in agreement with previous constraints from literature, therefore validating the accuracy of the applied method. Later calcite cements were dated at 13.2 ± 1.1 (), 10.2 ± 2.7 and 9.51 ± 0.77 Ma, implying multiple post-depositional fluid events. This study demonstrates the great potential of the U-Pb method for chronostratigraphy in continental systems, where correlations between time-equivalent lateral facies are often out of reach. In Miocene deposits the method yields a time resolution within the 3rd order depositional sequences (0.5–5 Ma).

Recovery of meteorites using an autonomous drone and machine learning

1Robert I. Citron,2,3Peter Jenniskens,4Christopher Watkins,5Sravanthi Sinha,6Amar Shah,7Chedy Raissi,8Hadrien Devillepoix,2Jim Albers
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13663]
1Department of Earth and Planetary Sciences, University of California, Davis, Davis, California, 95616 USA
2SETI Institute, Mountain View, California, 94043 USA
3NASA Ames Research Center, Moffett Field, California, 94035 USA
4Scientific Computing, Commonwealth Scientific and Industrial Research Organisation, Clayton, Victoria, 3181 Australia
5Holberton School of Software Engineering, San Francisco, California, 94111 USA
6Department of Engineering, Computational and Biological Learning, Cambridge University, Cambridge, CB2 1PZ UK
7Institut National de Recherche en Informatique et en Automatique, Villers-lès-Nancy, 54506 France
8Space Science & Technology Centre, School of Earth and Planetary Sciences, Curtin University, GPO Box U1987, Perth, Western Australia, 6845 Australia
Published by arrangement with John Wiley & Sons

The recovery of freshly fallen meteorites from tracked and triangulated meteors is critical to determining their source asteroid families. Even though our ability to locate meteorite falls continues to improve, the recovery of meteorites remains a challenge due to large search areas with terrain and vegetation obscuration. To improve the efficiency of meteorite recovery, we have tested the hypothesis that meteorites can be located using machine learning techniques and an autonomous drone. To locate meteorites autonomously, a quadcopter drone first conducts a grid survey acquiring top-down images of the strewn field from a low altitude. The drone-acquired images are then analyzed using a machine learning classifier to identify meteorite candidates for follow-up examination. Here, we describe a proof-of-concept meteorite classifier that deploys off-line a combination of different convolution neural networks to recognize meteorites from images taken by drones in the field. The system was implemented in a conceptual drone setup and tested in the suspected strewn field of a recent meteorite fall near Walker Lake, Nevada.

An evolutionary condensation sequence revealed by mineralogically-distinct nodules in fine-grained, spinel-rich inclusions from CV3 chondrites: Implications for the genetic links between different types of non-igneous refractory inclusions

1Shaofan Che,1Adrian J.Brearley
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.05.055]
1Department of Earth and Planetary Sciences, MSC03-2040, University of New Mexico, Albuquerque, NM 87131-0001, USA
Copyright Elsevier

Fine-grained, spinel-rich inclusions (FGIs) are abundant in CV3 chondrites and exhibit textures and compositions that are consistent with a condensation origin. We have conducted a systematic investigation of FGIs from two reduced CV3 chondrites, Leoville and Efremovka, which has revealed a number of microscale variations in the primary mineralogies and textures of nodules, and provided further insights into the origins of FGIs. Nodules in individual FGIs vary in size and exhibit variations in their mineralogical zonation, resulting in significant heterogeneity within each FGI. In individual FGIs, nodules with a small size (typically <10 μm) commonly form clusters, whereas larger nodules (often >20 μm) are either embedded in the mass of small nodules or occur as shells surrounding clusters of small nodules. The size difference is associated with a difference in mineralogy: small nodules typically contain single or a few spinel/melilite grains as cores, while the spinel/melilite cores of large nodules are polycrystalline and more compact. Transmission Electron Microscope observations show that the nodules have complex microstructures, including the presence of fine-grained spinel, the close association of fine-grained Al-Ti-diopside with spinel, and a crystallographic orientation relationship between adjacent clinoenstatite and diopside grains.

Our microstructural observations indicate that disequilibrium condensation played an important role in the formation of FGIs, consistent with some previous studies. Specifically, the presence of spinel-cored and melilite-dominant nodules, as well as the different occurrences of spinel (in the cores and on the periphery), suggest that formation of these nodules occurred under disequilibrium conditions, which may be caused by physical isolation of condensates.

Nodules in FGIs show textural and compositional similarities with other types of non-igneous CAIs: hibonite-spinel inclusions and fluffy Type A CAIs. We suggest that mineralogically-distinct nodules are micrometer-sized counterparts of different types of non-igneous CAIs and record an evolutionary condensation sequence in the solar nebula. It is likely that different nodules in individual FGIs formed in the same gaseous reservoir, but at different times. The mechanism of physical isolation of condensates probably controlled the accretion behavior of nodules with different mineralogies and sizes, resulting in the observed distribution patterns of nodules. On the other hand, some mineralogically-zoned FGIs, with a Mg-rich core and a Ca-rich mantle, can be better explained by condensation, followed by transport of the inclusions to a different region of the protoplanetary disk.

Tracing the origin and core formation of the enstatite achondrite parent bodies using Cr isotopes

1,3Ke Zhu(朱柯),1Frédéric Moynier,2Martin Schiller,3Harry Becker,4Jean-Alix Barrat,1,2Martin Bizzarro
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.05.053]
1Université de Paris, Institut de Physique du Globe de Paris, CNRS, 75005, Paris France
2Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, Øster Voldgade 5–7, Copenhagen DK-1350, Denmark
3Freie Universität Berlin, Institut für Geologische Wissenschaften, Malteserstr. 74-100, 12249 Berlin, Germany
4Univ. Brest, CNRS, UMR 6539 (Laboratoire des Sciences de l’Environnement Marin), LIA BeBEST, Institut Universitaire Européen de la Mer (IUEM), Place Nicolas Copernic, 29280 Plouzané, France
Copyright Elsevier

Enstatite achondrites (including aubrites) are the only differentiated meteorites that have similar isotope compositions to the Earth-Moon system for most of the elements. However, the origin and differentiation of enstatite achondrites and their parent bodies remain poorly understood. Here, we report high-precision mass-independent and mass-dependent Cr isotope data for 10 enstatite achondrites, including eight aubrites, Itqiy and one enstatite-rich clast in Almahatta Sitta, to further constrain the origin and evolution of their parent bodies. The ε54Cr (per 10,000 deviation of the mass bias corrected 54Cr/52Cr ratio from a terrestrial standard) systematics define three groups: main-group aubrites with ε54Cr = 0.06 ± 0.12 (2SD, N =7) that is similar to the enstatite chondrites and the Earth-Moon system, Shallowater aubrite with ε54Cr = -0.12 ± 0.04 and Itqiy-type meteorites with ε54Cr = -0.26 ± 0.03 (2SD, N =2). This shows that there were at least three enstatite achondrite parent bodies in the Solar System. This is confirmed by their distinguished mass-dependent Cr isotope compositions (δ53Cr values): 0.24 ± 0.03 ‰, 0.10 ± 0.03 ‰ and -0.03± 0.03 ‰ for main-group, Shallowater and Itqiy parent bodies, respectively. Aubrites are isotopically heavier than chondrites (δ53Cr =-0.12 ± 0.04 ‰), which likely results from the formation of an isotopically light sulfur-rich core. We also obtained the abundance of the radiogenic 53Cr (produced by the radioactive decay of 53Mn, T1/2= 3.7 million years). The radiogenic ε53Cr excesses correlate with the 55Mn/52Cr ratios for aubrites (except Shallowater and Bustee) and also the Cr stable isotope compositions (δ53Cr values). We show that these correlations represent mixing lines that also hold chronological significance since they are controlled by the crystallization of sulfides and silicates, which mostly reflect the main-group aubrite parent body differentiation at 4562.5 ± 1.1 Ma (i.e., 4.8 ± 1.1 Ma after Solar System formation). Furthermore, the intercept of these lines with the ordinate axis which represent the initial ε53Cr value of main-group aubrites (0.50 ± 0.16, 2σ) is much higher than the average ε53Cr value of enstatite chondrites (0.15 ± 0.10, 2SD), suggesting an early sulfur-rich core formation that effectively increased the Mn/Cr ratio of the silicate fraction of the main-group aubrite parent body.

Association of silica phases as geothermobarometer for eucrites: Implication for two-stage thermal metamorphism in the eucritic crust

1,2Haruka Ono,3Atsushi Takenouchi,1,4Takashi Mikouchi,3,5Akira Yamaguchi,6,7Masahiro Yasutake,8Akira Miyake,8,9,10Akira Tsuchiyama
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13664]
1Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
2Planetary Exploration Research Center, Chiba Institute of Technology, 2-17-1, Tsudanuma, Narashino, Chiba, 275-0016 Japan
3National Institute of Polar Research (NIPR), 10-3 Midori-cho, Tachikawa, Tokyo, 190-8518 Japan
4The University Museum, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
5Department of Polar Science, School of Multidisciplinary Science, SOKENDAI (The Graduate University for Advanced Studies), Tokyo, 190-8518 Japan
6Japan Synchrotron Radiation Research Institute (JASRI), SPring-8, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5198 Japan
7Research Organization of Science and Technology, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga, 525-8577 Japan
8Department of Geology and Mineralogy, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake, Sakyo-ku, Kyoto, 606-8502 Japan
9CAS Key Laboratory of Mineralogy and Metallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (CAS), Guangzhou, 510640 People’s Republic of China
10CAS Center for Excellence in Deep Earth Science, Guangzhou, 510640 People’s Republic of China
Published by arrangement with John Wiley & Sons

Silica mineral is present in different stable polymorphs depending on the temperature and pressure conditions of crystallization. We suggest using silica mineral phases to constrain the thermal history of eucrites. We focused on silica minerals in basaltic clasts of nine non-cumulate eucrites to compare with previously studied cumulate eucrites. Our observations indicate an apparent relationship between thermal metamorphic degrees and silica phase texture in basaltic clasts of non-cumulate eucrites. To reveal complex transformation relations between silica polymorphs in eucrites, we performed cooling experiments (cooling rate: 1 and 0.1 °C h−1) and heating experiments (heating 500 °C for 168 h and 800 °C for 96 h) using eucrites. The cooling experiments show that cristobalite is an initial silica phase crystallized from eucritic magma and transforms to quartz at the cooling rate between 0.1 and 1 °C h−1. Based on the cooling experiments and observations of eucrites, we suggest that a combination of silica minerals varies depending mainly on cooling rates. According to the heating experiments, monoclinic tridymite hardly transforms to other phases at low temperature by short reheating events such as brecciation. Monoclinic tridymite can partially transform to quartz with a “hackle” fracture. We conclude that a reheating event partially transformed monoclinic tridymite to quartz to form aggregates of monoclinic tridymite and quartz with the hackle fracture in eucrites. We suggested that some basaltic clasts in non-cumulate eucrites experienced two-stage thermal metamorphism in the eucritic crust. The first metamorphic event has resulted from burial under lava produced by successive eruptions. Igneous intrusions into the preformed crust may have caused the second metamorphic event. The intrusions heated the deep eucritic crust and induced the transformation from monoclinic tridymite to quartz.

Noble gases in CM carbonaceous chondrites: Effect of parent body aqueous and thermal alteration and cosmic ray exposure ages

1Daniela Krietsch,1Henner Busemann,1My E.I.Riebe,2,3Ashley J.King,4Conel M.O’D. Alexander,1Colin Maden
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.05.050]
1Institute of Geochemistry and Petrology, ETH Zurich, Clausiusstrasse 25, 8092 Zurich, Switzerland
2School of Physical Sciences, The Open University, Milton Keynes MK7 6AA, UK
3Planetary Materials Group, Natural History Museum, London SW7 5BD, UK
4Earth and Planets Laboratory, Carnegie Institution of Washington, 5241 Broad Branch Road, N. W., Washington, DC 20015, USA
Copyright Elsevier

Like most primitive carbonaceous chondrites, the CM chondrites experienced varying degrees of asteroidal aqueous alteration, which may have overprinted pre-accretionary processing. Several aqueous alteration scales for CM chondrites (and other carbonaceous chondrites) have been proposed based on alteration-dependent changes in various petrological and geochemical characteristics. Given the possibility that the intensity of aqueous alteration could be recorded in the primordial noble gas compositions, we test potential correlations between petrologic, geochemical and noble gas characteristics in a detailed study on 39 CM chondrites, including some of the most pristine CM chondrites identified to date, and 4 CM-related carbonaceous chondrites. We mainly compare our noble gas data with the alteration schemes proposed by Alexander et al. (2013) and Howard et al. (2015). In addition to the noble gas analyses, we determined the phyllosilicate fractions of 17 of the CM chondrites using X-ray diffraction (XRD) to complement missing data points in the Howard alteration scheme. The influence of post-hydration thermal modification on noble gases in CM chondrites is investigated by comparison of heated and unheated samples. Cosmic-ray exposure (CRE) ages are determined for all samples in this study as well as for 26 more samples based on CM chondrite literature noble gas data.

The noble gas inventory in CM chondrites represents a mixture of cosmogenic, radiogenic, and abundant primordially trapped noble gases. Additionally, about 50 % of our CM bulk samples contain detectable solar wind (SW), which implies that many but not all CM chondrites are regolith breccias or carry SW from a pre-accretion irradiation phase. Aqueous alteration affects primordial noble gas abundances and elemental and isotopic compositions in CM chondrites. In particular, the process causes loss of an Ar-rich component, different in elemental and isotopic composition to known noble gas components. This component is lost during the early stages of aqueous alteration until complete degassing of its carrier material (possibly upon at least partial destruction) below petrologic type of ∼1.5 on the Howard et al. (2015) scale. Likely, small amounts of Q gases were additionally released by aqueous alteration. Strong thermal modification at >750 °C results in a significant additional loss of noble gases, whereas peak temperatures <500 °C likely have minor effects on the noble gas inventories of CM chondrites. Some of the described trends of noble gas contents and elemental and isotopic ratios in this study are observable across multiple carbonaceous chondrite groups, in particular also the CR chondrites. Hence, these carbonaceous chondrites may have started with similar initial noble gas inventories due to accretion of material from a common reservoir. The CRE ages of most of our CM samples fall within the typical range of <10 Myr previously observed for CM chondrites. A few CM chondrites, however, show longer CRE ages, with the longest CRE age of ∼20 Myr determined for the SW-rich CM Allan Hills (ALH) 85013. The degree of aqueous and thermal alteration is variable among CM chondrites with similar CRE ages.

The Tarda Meteorite: A Window into the Formation of D-Type Asteroids

1Yves Marrocchi,2Guillaume Avice,3Jean-Alix Barrat
The Astrophysical Journal Letters, 913, L9 Link to Article [DOI https://doi.org/10.3847/2041-8213/abfaa3]
1Université de Lorraine, CNRS, CRPG, UMR 7358, Vandœuvre-lès-Nancy, F-54501, France; yvesm@crpg.cnrs-nancy.fr
2Université de Paris, Institut de physique du globe de Paris, CNRS, F-75005 Paris, France
3Université de Brest, CNRS, IRD, Ifremer, LEMAR, F-29280 Plouzané, France

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XAFS and XRD study on Fe, Ni, and Ge in iron meteorite NWA 859

1Shao H.,1Isobe H.,1Kitahara G.,2Fukui H.,1Yoshiasa A.
Physics and Chemistry of Minerals 48, 11 Link to Article [DOI 10.1007/s00269-021-01136-8]
1Department of Earth and Environmental Sciences, Faculty of Advanced Science and Technology, Kumamoto University, Kumamoto, 860-8555, Japan
2Department of Material Science, Graduate School of Material Science, University of Hyogo, Hyogo, 678-1297, Japan

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Synthesis and characterization of Fe(III)-Fe(II)-Mg-Al smectite solid solutions and implications for planetary science

1,2Valerie K. Fox et al. (>10)
American Mineralogist 106, 964–982 Link to Article [DOI: https://doi.org/10.2138/am-2020-7419CCBYNCND]
1California Institute of Technology, 1200 E. California Boulevard, Pasadena, California 91125, U.S.A
2University of Minnesota, John T. Tate Hall, 116 Church Street
SE, Minneapolis, MN 55455-0149, U.S.A.
Copyright: The Mineralogical Society of America

This study demonstrates the synergies and limits of multiple measurement types for the detection
of smectite chemistry and oxidation state on planetary surfaces to infer past geochemical conditions.
Smectite clay minerals are common products of water-rock interactions throughout the solar system,
and their detection and characterization provides important clues about geochemical conditions and past
environments if sufficient information about their composition can be discerned. Here, we synthesize
and report on the spectroscopic properties of a suite of smectite samples that span the intermediate
compositional range between Fe(II), Fe(III), Mg, and Al end-member species using bulk chemical
analyses, X‑ray diffraction, Vis/IR reflectance spectroscopy, UV and green-laser Raman spectroscopy,
and Mössbauer spectroscopy. Our data show that smectite composition and the oxidation state of octahedral Fe can be reliably identified in the near infrared on the basis of combination and fundamental
metal-OH stretching modes between 2.1–2.9 μm, which vary systematically with chemistry. Smectites
dominated by Mg or Fe(III) have spectrally distinct fundamental and combination stretches, whereas
Al-rich and Fe(II)-rich smectites have similar fundamental minima near 2.76 μm, but have distinct
combination M-OH features between 2.24 and 2.36 μm. We show that with expanded spectral libraries that include intermediate composition smectites and both Fe(III) and Fe(II) oxidation states, more
refined characterization of smectites from MIR data is now possible, as the position of the 450 cm–1
absorption shifts systematically with octahedral Fe content, although detailed analysis is best accomplished in concert with other characterization methods. Our data also provide the first Raman spectral
libraries of smectite clays as a function of chemistry, and we demonstrate that Raman spectroscopy
at multiple excitation wavelengths can qualitatively distinguish smectite clays of different structures
and can enhance interpretation by other types of analyses. Our sample set demonstrates how X-ray
diffraction can distinguish between dioctahedral and trioctahedral smectites using either the (02,11) or
(06,33) peaks, but auxiliary information about chemistry and oxidation state aids in specific identifications. Finally, the temperature-dependent isomer shift and quadrupole splitting in Mössbauer data are
insensitive to changes in Fe content but reliability differentiates Fe within the smectite mineral structure.

Widespread Tissintite in Strongly Shock-Lithified Lunar Regolith Breccias

1,2Zhang A.-C.,1,3Jiang Q.-T.,4Tomioka N.,5Guo Y.-J.,1Chen J.-N.,2,6Li Y.,7Sakamoto N.,7,8Yurimoto H.
Geophysical Research Letters 48, e2020GL091554 Link to Article [DOI 10.1029/2020GL091554]
1State Key Laboratory for Mineral Deposits Research, School of Earth Science and Engineering, Nanjing University, Nanjing, China
2CAS Center for Excellence in Comparative Planetology, Hefei, China
3Now at Department of Geology & Geophysics, Yale University, New Haven, United States
4Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Nankoku, Japan
5CAS Key Laboratory of Standardization and Measurement for Nanotechnology, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing, China
6Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
7Isotope Imaging Laboratory, Creative Research Institution, Hokkaido University, Sapporo, Japan
8Department of Natural History Sciences, Hokkaido University, Sapporo, Japan

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