¹Stefan Farsang,²Ian A. Franchi,^,Xuchao Zhao,³Timothy D. Raub,⁴Simon A.T. Redfern,^2,5Monica M. Grady
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13647]
¹Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ UK
²School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA UK
³School of Earth & Environmental Sciences, University of St Andrews, Irvine Building, St Andrews, KY16 9AL UK
⁴Asian School of the Environment, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798 Singapore
⁵Department of Earth Sciences, Natural History Museum, Cromwell Rd, London, SW7 5BD UK
Published by arrangement with John Wiley & Sons

The paragenesis of carbonates in the Cold Bokkeveld CM chondrite is determined from a detailed petrographic, chemical, spectroscopic, and isotopic study of nine associations of carbonates (aragonite, calcite, and dolomite) with other secondary minerals that occur within the meteorite. Our study reveals the existence of carbonates displaying petrographic features that are distinct from those of type 1 and type 2 carbonates commonly observed in CM2 meteorites. These include carbonates interstitial to octahedral magnetite crystals, for which a new designation of “type 1c” is suggested. The O isotopic values of dolomite (δ¹⁸O ranging from +21.1 to +25.8‰ and Δ¹⁷O from −4.9 to −4.0‰) are similar to those measured in dolomites from other CM chondrites. The presence of complex carbonates with a CaCO₃ core and Mg‐enriched rim implies several generations of fluids and/or their evolving composition on the CM parent body(ies). Petrographic characteristics indicate at least six stages of potentially overlapping carbonate and phyllosilicate formation events. We show that type 1 and type 2 calcite have distinct Raman spectral characteristics. Type 1 calcite is characterized by very broad peaks, whereas type 2 calcite displays narrow peaks similar to those of typical abiotic terrestrial calcite, suggesting high crystallinity. A carbonate Raman spectrum showing features characteristic of both aragonite and calcite likely documents an aragonite‐calcite phase transition. Raman spectroscopy also reveals the presence of organic matter in the majority of carbonates. This indicates that organic carbon was mobilized by aqueous fluids for extended periods.

¹Annarita Franza,²Marco Morelli,²Daniela Faggi,^1,3Giovanni Pratesi
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13654]
¹Department of Earth Sciences, University of Firenze, via G. La Pira 4, 50122 Florence, Italy
²Fondazione PARSEC, Via Galcianese 20/h, 59100 Prato, Italy
³INAF‐IAPS, Istituto di Astrofisica e Planetologia Spaziali, Via Fosso del Cavaliere 100, 00133 Rome, Italy
Published by arrangement with John Wiley & Sons

This work focuses on the historical and scientific investigation of a presumed meteorite fall that occurred in the Sicilian township of Marsala in 1834. Preliminary studies have classified this phenomenon as a “doubtful meteorite.” This term describes, according to the Nomenclature Committee of the Meteoritical Society, an object for which there was significant uncertainty over whether it was a real meteorite or, in some cases, whether it ever existed. Thanks to the analysis of untapped sources, the first objective of this work is to clarify the nature of the event. Subsequently, the results of the minero‐chemical analyses that were performed, in 1835, on two fragments recovered after the event are discussed for the first time. This work then shows the collecting history of one of the presumed meteorite specimens. Based on the results presented here, this work highlights the role of doubtful meteorites as a fundamental resource for the history of meteoritics and meteorite collecting as well as for studying the processes that have led to the scientific study of meteorites.

¹Aryavart Anand,^1,2Jonas Pape,¹Martin Wille,¹Klaus Mezger
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.04.029]
¹Institut für Geologie, Universität Bern, Baltzerstrasse 1+3, 3012 Bern, Switzerland
²Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
Copyright Elsevier

The 53Mn-53Cr isotope systematics in ordinary chondrites constrains the accretion and thermal history of their parent bodies. Mineralogical observations and olivine-spinel geothermometry suggest that chromite in ordinary chondrites formed during prograde thermal metamorphism with the amount of chromite increasing with petrologic grades in type 3 to type 6 ordinary chondrites. Assuming a chondritic evolution of the respective parent bodies, 53Cr/52Cr model ages for chromite range from to Ma after the formation of calcium-aluminium-rich inclusions (CAIs). Chromite and silicate-metal-sulphide isochrons define an age range from to Ma. Both chromite model ages and isochron ages correlate with the petrological grade of the samples, which is consistent with an onion-shell structure of the chondrite parent bodies. The study shows that unlike the isochron ages, which are prone to impact-related disturbances or partial re-equilibration during cooling from high temperatures, the chromite model ages are not easily affected by thermal metamorphism or later events and yield robust mineral growth ages. The results are consistent with a homogenous distribution of 53Mn and an initial canonical 53Mn/55Mn = 6.28 x 10-6. The estimated closure temperatures for the Mn-Cr system in chromites range from ∼760 °C for type 6 to ∼540-620 °C for type 3 ordinary chondrites. The high closure temperatures estimated for type 3 and type 6 ordinary chondrites imply that the chromite ages correspond to the peak metamorphic temperature reached during the thermal history of the chondrite parent bodies. The oldest chromite model age obtained for type 3 samples along with the established Al-Mg chondrule formation ages constrain the accretion of the parent bodies to > 2.1 Ma after CAI formation, implying that planetesimal accretion immediately followed chondrule formation.