¹Jan Leitner,²Knut Metzler,³Christian Vollmer,⁴Christine Floss,⁴Pierre Haenecour,¹János Kodolányi,⁵Dennis Harries,¹Peter Hoppe
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13412]
¹Max Planck Institute for Chemistry, Particle Chemistry Department, Hahn‐Meitner‐Weg 1, 55128 Mainz, Germany
²Institute for Planetology, University of Münster, 48149 Münster, Germany
³Institute for Mineralogy, University of Münster, 48149 Münster, Germany
⁴Laboratory for Space Sciences, Physics Department and McDonnell Center for Space Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, Missouri, 63130 USA
⁵Institute of Geoscience, Friedrich Schiller University Jena, Carl‐Zeiss‐Promenade 10, 07745 Jena, Germany
Published by arrangement with John Wiley & Sons

We investigated the inventory of presolar silicate, oxide, and silicon carbide (SiC) grains of fine‐grained chondrule rims in six Mighei‐type (CM) carbonaceous chondrites (Banten, Jbilet Winselwan, Maribo, Murchison, Murray and Yamato 791198), and the CM‐related carbonaceous chondrite Sutter’s Mill. Sixteen O‐anomalous grains (nine silicates, six oxides) were detected, corresponding to a combined matrix‐normalized abundance of ~18 ppm, together with 21 presolar SiC grains (~42 ppm). Twelve of the O‐rich grains are enriched in ¹⁷O, and could originate from low‐mass asymptotic giant branch stars. One grain is enriched in ¹⁷O and significantly depleted in ¹⁸O, indicative of additional cool bottom processing or hot bottom burning in its stellar parent, and three grains are of likely core‐collapse supernova origin showing enhanced ¹⁸O/¹⁶O ratios relative to the solar system ratio. We find a presolar silicate/oxide ratio of 1.5, significantly lower than the ratios typically observed for chondritic meteorites. This may indicate a higher degree of aqueous alteration in the studied meteorites, or hint at a heterogeneous distribution of presolar silicates and oxides in the solar nebula. Nevertheless, the low O‐anomalous grain abundance is consistent with aqueous alteration occurring in the protosolar nebula and/or on the respective parent bodies. Six O‐rich presolar grains were studied by Auger Electron Spectroscopy, revealing two Fe‐rich silicates, one forsterite‐like Mg‐rich silicate, two Al‐oxides with spinel‐like compositions, and one Fe‐(Mg‐)oxide. Scanning electron and transmission electron microscopic investigation of a relatively large silicate grain (490 nm × 735 nm) revealed that it was crystalline åkermanite (Ca₂Mg[Si₂O₇]) or a an åkermanite‐diopside (MgCaSi₂O₆) intergrowth.

¹Steven Goderis¹Bastien Soens,^1,2Matthew S.Huber,^1,3,4Seann McKibbin,⁵Matthias van Ginneken,¹Flore Van Maldeghem,⁶Vinciane Debaille,⁷Richard C.Greenwood,⁷Ian A.Franchi,⁸ Veerle Cnudde,¹⁰Stijn Van Malderen,¹⁰ Frank Vanhaecke,^11,12Christian Koeberl,¹²Dan Topal,¹Philippe Claeys
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.11.016]
¹Analytical-, Environmental-, and Geo-Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium
²Department of Geology, University of the Free State, 205 Nelson Mandela Dr., Bloemfontein 9300, South Africa1
³Institut für Erd- und Umweltwissenschaften, Universität Potsdam, Haus 27, Karl-Liebknecht-Straße 24-25, Potsdam-Golm 14476, Germany1
⁴Geowissenschaftliches Zentrum, Abteilung Isotopengeologie, Georg-August-Universität Göttingen, Goldschmidtstraße 1, Göttingen 37073, Germany1
⁵Royal Belgian Institute of Natural Sciences, 29 Rue Vautier, B-1000 Brussels, Belgium
⁶Laboratoire G-Time, Université Libre de Bruxelles 50, Av. F.D. Roosevelt CP 160/02, B-1050 Brussels, Belgium
⁷Planetary and Space Sciences, School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom
⁸Department of Geology, Ghent University, Campus Sterre, Krijgslaan 281 – S8, B-9000 Ghent, Belgium
⁹Department of Earth Sciences, Utrecht University, Princetonlaan 8a, 3584CB Utrecht, the Netherlands
¹⁰Department of Chemistry, Ghent University, Krijgslaan, 281 – S12, B-9000 Ghent, Belgium
¹¹Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
¹²Natural History Museum, Burgring 7, A-1010 Vienna, Austria

A newly discovered sedimentary accumulation of micrometeorites in the Sør Rondane Mountains of East Antarctica, close to the Widerøefjellet summit at ∼2750 meter above sea level, is characterized in this work. The focus here lies on 2099 melted cosmic spherules larger than 200 μm, extracted from 3.2 kg of sampled sediment. Although the Widerøefjellet deposit shares similarities to the micrometeorite traps encountered in the Transantarctic Mountains, both subtle and more distinct differences in the physicochemical properties of the retrieved extraterrestrial particles and sedimentary host deposits are discernable (e.g., types of bedrock, degree of wind exposure, abundance of metal-rich particles). Unlike the Frontier Mountain and Miller Butte sedimentary traps, the size fraction below 240 μm indicates some degree of sorting at Widerøefjellet, potentially through the redistribution by wind, preferential alteration of smaller particles, or processing biases. However, the cosmic spherules larger than 300 μm appear largely unbiased following their size distribution, frequency by textural type, and bulk chemical compositions. Based on the available bedrock exposure ages for the Sør Rondane Mountains, extraterrestrial dust is estimated to have accumulated over a time span of ∼1 to 3 Ma at Widerøefjellet. Consequently, the Widerøefjellet collection reflects a substantial reservoir to sample the micrometeorite influx over this time interval. Petrographic observations and 3D microscopic CT imaging are combined with chemical and triple-oxygen isotopic analyses of silicate-rich cosmic spherules larger than 325 μm. The major element composition of 49 cosmic spherules confirms their principally chondritic parentage. For 18 glassy, 15 barred olivine, and 11 cryptocrystalline cosmic spherules, trace element concentrations are also reported on. Based on comparison with evaporation experiments reported in literature and accounting for siderophile and chalcophile element losses during high-density phase segregation and ejection, the observed compositional sequence largely reflects progressive heating and evaporation during atmospheric passage accompanied by significant redox shifts, although the influence of (refractory) chondrite mineral constituents and terrestrial alteration cannot be excluded in all cases. Twenty-eight cosmic spherules larger than 325 μm analyzed for triple-oxygen isotope ratios confirm inheritance from mostly carbonaceous chondritic precursor materials (∼55% of the particles). Yet, ∼30% of the measured cosmic spherules and ∼50% of all glassy cosmic spherules are characterized by oxygen isotope ratios above the terrestrial fractionation line, implying genetic links to ordinary chondrites and parent bodies currently unsampled by meteorites. The structural, textural, chemical, and isotopic characteristics of the cosmic spherules from the Sør Rondane Mountains, and particularly the high proportion of Mg-rich glass particles contained therein, imply a well-preserved and representative new sedimentary micrometeorite collection from a previously unstudied region in East Antarctica characterized by distinct geological and exposure histories.