The aqueous alteration of GEMS-like amorphous silicate in a chondritic micrometeorite by Antarctic water

1,2,3M.D.Suttle,2,4L.Folco,1,3M.J.Genge,5I.A.Franchi,2,6F.Campanale,6E.Mugnaioli,6X.Zhao
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.11.006]
1Planetary Materials Group, Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, UK
2Dipartimento di Scienze della Terra, Università di Pisa, 56126 Pisa, Italy
3Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College London, South Kensington, London, SW7 2AZ, UK
4CISUP, Centro per l’Integrazione della Strumentazione dell’Università di Pisa, Lungarno Pacinotti 43, 56126 Pisa, Italy
5School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
6Center for Nanotechnology Innovation @NEST, Istituto Italiano di Tecnologia (IIT), Piazza San Silvestro 12, 56127 Pisa, Italy
Copyright Elsevier

We analysed the heterogenous fine-grained (sub-μm) matrix of a small (58×93μm), unmelted and minimally heated (<350°C) micrometeorite (CP94-050-052) recovered from Antarctic blue ice. This particle contains some unaltered highly primitive phases, including refractory anhydrous high-Mg silicates and submicron crystalline needle-shaped acicular grains interpreted as enstatite whiskers. The particle also contains an abundance of micron-sized Fe-rich grains, which span a compositional and textural continuum between amorphous oxygen-rich silicate and poorly crystalline Fe-rich phyllosilicate (cronstedtite). These Fe-rich grains are here interpreted as secondary phases formed by aqueous alteration. Their inferred anhydrous precursors were likely primitive “GEMS-like” amorphous Fe-Mg-silicates. This micrometeorite’s bulk chemical composition and mineralogy suggest either a carbonaceous chondrite or cometary origin. However, the particle’s average O-isotope composition (δ17O: -12.4‰ [±5.0‰], δ18O: -24.0‰ [±2.3‰] and Δ17O at +0.1‰ [±4.8‰] is distinct from all previously measured chondritic materials. Instead this value is intermediate between primitive chondritic materials and the composition of Antarctic water – strongly implying that the particle was heavily affected by Antarctic alteration. Analysis of the micrometeorite’s H-isotopes reveals low deuterium abundances (δD: -217‰ to -173‰ [±43-47‰]) paired with high H abundances (and thus high water contents [<25wt.%]). Although both water contents and H-isotope compositions overlap with those reported in CM chondrites, the datapoints measured from CP94-050-052 extend to more extreme values. Further supporting the idea that the aqueous alteration that affected this micrometeorite operated under different environmental conditions to asteroidal settings. These data collectively demonstrate partial isotopic exchange with light (δ18O-poor, δD-poor) terrestrial fluids whilst the micrometeorite resided in Antarctica. Although this micrometeorite may have been aqueously altered whilst on its parent body this cannot be conclusively demonstrated due to the extent of the weathering overprint. Antarctic alteration operated at significantly higher water-to-rock ratios than chondritic settings. Despite these differences the extent of secondary replacement and the duration of alteration were limited with mafic silicates remaining unaffected. The combined alteration conditions for this particle likely operated over short timescales (<24hrs), under mildly alkaline conditions (∼pH8) and at low temperatures (<50°C), this could have occurred during the micrometeorite’s extraction from blue ice.

Origin of isolated olivine grains in carbonaceous chondrites

1Emmanuel Jacquet,2Maxime Piralla,2Pauline Kersaho,2Yves Marrocchi
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13583]
1Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), Muséum national d’Histoire naturelle, Sorbonne Université, CNRS, CP52 57 rue Cuvier, 75005 Paris, France
2Centre de Recherches Pétrographiques et Géochimiques, CNRS, Université de Lorraine, UMR 7358,, 54501 Vandœuvre‐lès‐Nancy, France
Published by arrangement with John Wiley & Sons

We report microscopic, cathodoluminescence, chemical, and O isotopic measurements of FeO‐poor isolated olivine grains (IOG) in the carbonaceous chondrites Allende (CV3), Northwest Africa 5958 (C2‐ung), Northwest Africa 11086 (CM2‐an), and Allan Hills 77307 (CO3.0). The general petrographic, chemical, and isotopic similarity with bona fide type I chondrules confirms that the IOG derived from them. The concentric CL zoning, reflecting a decrease in refractory elements toward the margins, and frequent rimming by enstatite are taken as evidence of interaction of the IOG with the gas as stand‐alone objects. This indicates that they were splashed out of chondrules when these were still partially molten. CaO‐rich refractory forsterites, which are restricted to ∆17O <−4‰ likely escaped equilibration at lower temperatures because of their large size and possibly quicker quenching. The IOG thus bear witness to frequent collisions in the chondrule‐forming regions.

Reassessing the thermal history of martian meteorite Shergotty and Apollo mare basalt 15555 using kinetic isotope fractionation of zoned minerals

1Frank Richter,2Lee M.Saper,3Johan Villeneuve,4Marc Chaussidon,5E.Bruce Watson,1Andrew M.Davis,1Ruslan A.Mendybaev,6Steven B.Simon
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.11.002]
1The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA
2California Institute of Technology, Pasadena, CA, USA
3CRPG, Universite’ de Lorraine, Nancy, France
4Institut de Physique du Globe de Paris, Paris, France
5Rensselaer Polytechnic Institute, Troy, NY, USA
6University of New Mexico, Albuquerque, NM, USA
Copyright Elsevier

Elemental abundance and isotopic fractionation profiles across zoned minerals from a martian meteorite (Shergotty) and from a lunar olivine-normative mare basalt (Apollo 15555) were used to place constraints on the thermal evolution of their host rocks. The isotopic measurements were used to determine the extent to which diffusion was responsible for, or modified, the zoning. The key concept is that mineral zoning that is the result of diffusion, or that was significantly affected by diffusion, will have an associated diagnostic isotopic fractionation that can quantify the extent of mass transfer by diffusion. Once the extent of diffusion was determined, the mineral zoning was used to constrain the thermal history. An isotopic and chemical profile measured across a large zoned pigeonite grain from Shergotty showed no significant isotopic fractionation of either magnesium or lithium, which is evidence that the chemical zoning was dominantly the result of crystallization from an evolving melt and that the crystallization must have taken place at a sufficiently fast rate that there was not time for any significant mass transfer by diffusion. Model calculations for the evolution of the fast-diffusing lithium showed that this would have required a cooling at a rate of about ∼ 150˚C/h or more. Measurable isotopic fractionation across a zoned olivine grain from lunar mare basalt 15555 indicated that the chemical zoning was mainly due to crystallization that was modified by a small but quantifiable amount of diffusion. The results of a diffusion calculation that was able to account for the amplitude and spatial scale of the isotopic fractionation across the olivine grain yielded an estimate of 0.2˚C/h for the cooling rate of 15555. The results of an earlier study of zoned augite and olivine grains from martian nakhlite meteorite NWA 817 were reviewed for comparison with the results from Shergotty. The isotopic fractionations near the edges of grains from NWA 817 showed that, in contrast to Shergotty, the lithium zoning in augite and of magnesium in olivine was due entirely to diffusion. The isotopic fractionation data across zoned minerals from the martian meteorites and from the lunar basalt were key for documenting and quantifying the extent of mass transfer by diffusion, which was a crucial step for validating the use of diffusion modeling to estimate their cooling rates.

Astronomical context of Solar System formation from molybdenum isotopes in meteorite inclusions

1,2Gregory A. Brennecka,2Christoph Burkhardt,2,3Gerrit Budde,1,4Thomas S. Kruijer,5Francis Nimmo,2Thorsten Kleine
Science 370, 837-840 Link to Article [DOI: 10.1126/science.aaz8482]
1Lawrence Livermore National Laboratory, Livermore, CA, USA.
2Institut für Planetologie, University of Münster, Münster, Germany.
3Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA.
4Museum für Naturkunde, Leibniz Institute for Evolution and Biodiversity Science, Berlin, Germany.
5Department of Earth & Planetary Sciences, University of California Santa Cruz, Santa Cruz, CA, USA.
Reprinted with permission from AAAS

Calcium-aluminum–rich inclusions (CAIs) in meteorites are the first solids to have formed in the Solar System, defining the epoch of its birth on an absolute time scale. This provides a link between astronomical observations of star formation and cosmochemical studies of Solar System formation. We show that the distinct molybdenum isotopic compositions of CAIs cover almost the entire compositional range of material that formed in the protoplanetary disk. We propose that CAIs formed while the Sun was in transition from the protostellar to pre–main sequence (T Tauri) phase of star formation, placing Solar System formation within an astronomical context. Our results imply that the bulk of the material that formed the Sun and Solar System accreted within the CAI-forming epoch, which lasted less than 200,000 years.

Oxygen-isotope systematics of chondrules and olivine fragments from Tagish Lake C2 chondrite: Implications of chondrule-forming regions in protoplanetary disk

1Takayuki Ushikubo,2Makoto Kimura
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.11.003]
1Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 200 Monobe-otsu, Nankoku, Kochi 783-8502 Japan
2National Institute for Polar Research, 10-3 Midoricho, Tachikawa, Tokyo 190-8518 Japan
Copyright Elsevier

Oxygen-isotope ratios of olivine in type I (MgO-rich) and type II (FeO-rich) chondrules and olivine fragments in the matrix from the Tagish Lake meteorite (C2-anomalous) were measured to understand the characteristics of the formation environment of the Tagish Lake chondrules. Of the 43 samples analyzed, 31 are MgO-rich and 16O-rich (Δ17O ∼ −5‰ [= δ17O – 0.52 × δ18O]), which is typical of chondrules in CM, CO, and CV chondrites. Six samples are FeO-rich and 16O-poor (Δ17O ∼ −2‰), while three samples are FeO-rich chondrules with Δ17O ≥ 0‰, the latter being a major component of chondrules and similar to the majority of crystalline silicates recovered from comet Wild 2.
Copyright Elsevier

The correlation between Mg# [= MgO / (MgO + FeO) mol %] and Δ17O values of the samples defines an intermediate trend between those of CM chondrite chondrules and comet Wild 2 samples. Assuming that the CM chondrites, Tagish Lake meteorite, and comet Wild 2 represent C-type asteroids, D-type asteroids, and Kuiper belt objects, respectively, the results of this study indicate that type II chondrules with Δ17O ≥ 0‰ formed at a location much farther out than that where the Tagish Lake meteorite parent body accreted, more than 3.1 million years after the CAI formation assuming homogeneous distribution of 26Al in the early Solar System (Tenner et al., 2019). These two aspects, namely the broad range of heliocentric distance and the prolonged period of chondrule formation, are important constraints when considering appropriate mechanisms of chondrule formation in the protoplanetary disk.

Laboratory photometry of regolith analogues: Effect of porosity-II

1A.Kar,1A.K.Sen,2R.Gupta
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114211]
1Department of Physics, Assam University, Silchar 788011, India
2IUCAA, Ganeshkhind, Pune 411007, India
Copyright Elsevier

Context:
Numerous minor bodies of our solar system are covered by loosely bound dust particles; these layers are called regolith. Light scattered by regolith surfaces is a function of their bulk porosity, of the sizes, shapes, structures and compositions of the constituent particles.

Aims:
To increase our data base, the present work is an extension of our previous work by Kar et al. (2016), where we reported light scattering data for regolith surfaces with different porosities, sizes, and composition of the particles (from very low to moderate absorption). The new samples have larger particles with moderate to high absorption, three originate from industry, and three are natural (among them a mixture of two previously studied samples).

Methods:
The samples were prepared with different bulk porosities. Photometric phase curves were built for two different geometrical configurations. The light source was a He-Ne laser at 632.8 nm. The phase angle () covered for the first configuration is from 45 to 126° and for the second configuration it is from 45 to 108°, in steps of 9 and 4.5° respectively. We maintained incident angle ()= emergent angle () for the first configuration and , while varying for the second configuration. The experimental data were fitted successfully to the semi-empirical model proposed by Hapke (2008) and interpreted in terms of the porosities and sizes of the particles. The albedo values obtained from the model for two samples are compared to those calculated directly from Mie theory.

Results:
The successful fit by the model is confirmed just as the increase of reflectivity with the decrease of porosities for a given composition and particle size. Further, it was observed that reflectivity increases with the decrease in particle size for a given composition.

Finally, we have tested that for corundum and silicon carbide samples with a and particle sizes ( respectively), the best fitted albedo () values that can be obtained from Hapke model, match very well with those calculated directly by Mie Theory. This also re-validated our approach adopted in the present work.

Near-infrared spectroscopy of the Sulamitis asteroid family: Surprising similarities in the inner belt primitive asteroid population

1Anicia Arredondo,1Humberto Campins,2Noemi Pinilla-Alonso,3,4Juliade León,5,3Vania Lorenzi,3,6David Morate
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114210]
1Physics Department, University of Central Florida, P.O. Box 162385, Orlando, FL 32816, USA
2Florida Space Institute, University of Central Florida, Orlando, FL 32816, USA
3Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
4Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
5Fundación Galileo Galilei – INAF, La Palma (TF), Spain
6Observatório Nacional, Coordenação de Astronomia e Astrofísica, 20921-400 Rio de Janeiro, Brazil
Copyright Elsevier

We present NIR spectra of 19 asteroids in the Sulamitis family as part of our survey of primitive inner belt asteroid families. The spectra were obtained with NASA’s Infrared Telescope Facility and the Telescopio Nazionale Galileo between January 2017 and February 2020. We find spectral homogeneity in our sample despite the diversity within the family observed at visible wavelengths. The average Sulamitis spectrum is flat with a spectral slope of 0.89 ± 0.26%/1000 Å between 0.95 and 2.3 μm. We show that the Sulamitis family is spectrally similar to other inner belt families in the NIR, despite differences between families seen in the visible wavelength range. We also compare our obtained spectra with asteroids (101955) Bennu and (162173) Ryugu to show that the Sulamitis family is a plausible source of Ryugu.

High-pressure phases in the Dhofar 922 L6 chondrite: Crystallization of olivine-ringwoodite aggregates and jadeite from melt

1Bazhan, I.S.,2,3Litasov, K.D.,4Badyukov, D.D.
Russian Geology and Geophysics 61, 241-249 Link to Article [DOI: 10.15372/RGG2019072]
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russian Federation
2Vereshchagin Institute for High Pressure Physics, Russian Academy of Sciences, Kaluzhskoe shosse 14, Troitsk, Moscow, 108840, Russian Federation
3Fersman Mineralogical Museum, Russian Academy of Sciences, Leninsky pr. 18/2, Moscow, 119071, Russian Federation
4Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 19, Moscow, 119991, Russian Federation

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