¹Tamara E. Koch,¹Dominik Spahr,¹Beverley J. Tkalcec,²Oliver Christ,¹Philomena-Theresa Genzel,¹Miles Lindner,¹David Merges,³Fabian Wilde,¹Björn Winkler,^1,4Frank E. Brenker
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13815]
¹Institute of Geosciences, Goethe University Frankfurt, Altenhoeferallee 1, 60438 Frankfurt am Main, Germany
²Department of Geoscience, University of Padua, Via Gradenigo 6, 35131 Padua, Italy
³Helmholtz-Zentrum Hereon, Max-Planck Strasse 1, 21502 Geesthacht, Germany
⁴Hawai‘i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at Mānoa, 1680 East-West Road, Honolulu, Hawaii, 96822 USA
Published arrangement with John Wiley & Sons

In order to gain further insights into early solar system aggregation processes, we carried out an experiment on board the International Space Station, which allowed us to study the behavior of dust particles exposed to electric arc discharges under long-term microgravity. The experiment led to the formation of robust, elongated, fluffy aggregates, which were studied by scanning electron microscopy, electron backscatter diffraction, and synchrotron micro-computed tomography. The morphologies of these aggregates strongly resemble the typical shapes of fractal fluffy-type calcium-aluminum-rich inclusions (CAIs). We conclude that a small amount of melting could have supplied the required stability for such fractal structures to have survived transportation and aggregation to and compaction within planetesimals. Other aggregates produced in our experiment have a massy morphology and contain relict grains, likely resulting from the collision of grains with different degrees of melting, also observed in some natural CAIs. Some particles are surrounded by igneous rims, which remind in thickness and crystal orientation of Wark–Lovering rims; another aggregate shows similarities to disk-shaped CAIs. These results imply that a (flash-)heating event with subsequent aggregation could have been involved in the formation of different morphological CAI characteristics.

¹Svetlana N. Teplyakova,¹Cyril A. Lorenz,¹Marina A. Ivanova,²Munir Humayun,¹Nataliya N. Kononkova,³Sergey E. Borisovsky,¹Alexander V. Korochantsev,⁴Ian A. Franchi,⁵Nina G. Zinovieva
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13814]
¹Vernadsky Institute of Geochemistry and Analytical Chemistry, Moscow, 119991 Russia
²National High Magnetic Field Laboratory and Department of Earth, Ocean & Atmospheric Science, Florida State University, 1800 E. Paul Dirac Drive, Tallahassee, Florida, 32310 USA
³Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry RAS, Staromonetnyi per, 35, Moscow, 119017 Russia
⁴Planetary and Space Sciences Research Institute, Open University, Milton Keynes, MK7 6AA UK
⁵Lomonosov Moscow State University, GSP-1, Leninskie Gory, Moscow, 119991 Russia
Published by arrangement with John Wiley & Sons

Karavannoe is a pallasite found in Russia in 2010. The mineralogy, chemistry, and oxygen isotopic composition indicate that Karavannoe is a member of the Eagle Station Pallasite (ESP) group. Karavannoe contains mostly olivine and subdued interstitial Fe,Ni-metal. Zoned distribution of FeO in small, rounded grains of olivine and FeO and Al2O3 in chromite shows that the cooling rate of the melt was fast during the crystallization of the round olivine grains. Siderophile element distribution and correlations of Au-As and Os-Ir concentrations in Karavannoe and the other ESP metal record its magmatic origin. FeO-rich composition of olivine, low W and Ga, and high Ni abundances in the Karavannoe metal indicate the formation of the metal from an oxidized chondrite precursor. Model calculations demonstrate that the ESPs’ metal compositions correspond to the solids of the fractional crystallization of CV- or CO-chondrite-derived metallic liquids. The Karavannoe metal composition corresponds to the solid fraction crystallized after ~40% fractional crystallization. The Mg/(Mg+Fe) atom ratio of complementary silicate liquid corresponds to Fo70, possibly indicating that the olivine is not in equilibrium with the metal and could have been a product of the late evolutionary processes in the Karavannoe parent body mantle. In any ESP genesis Karavannoe was not in equilibrium with its metal and is a product of mantle differentiation processes. Olivine of Karavannoe and ESPs is similar in composition, while the metal is different. We propose a model of ESP formation involving an impact-induced intrusion of liquid core metal into a basal mantle layer, followed by fractional crystallization of the metal. The metal textures and chemical zoning of Karavannoe minerals point to remelting and rapid cooling due to a later impact event.