¹Michael W.Broadley,¹David V.Bekaert,¹ Bernard Marty,²Akira Yamaguchi,³Jean-Alix Barrat
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.11.032]
¹Centre de Recherches Pétrographiques et Géochimiques, UMR 7358 CNRS—Université de Lorraine, 15 rue Notre Dame des Pauvres, BP 20, F-54501 Vandoeuvre-lès-Nancy, France
²National Institute of Polar Research, Tachikawa, Tokyo 190-8518, Japan
³Laboratoire Geoscience Océan, UMR 6538 CNRS—Université de Bretagne Occidentale et Institut Universitaire Européen de la Mer, Place Nicolas Copernic, 29280 Plouzané, France
Copyright Elsevier

Ureilites are equilibrated carbon-rich olivine-pyroxene rocks from the partially melted mantle of a large (>500 km diameter) heterogeneous parent body. Recently the ureilite parent body was interpreted as an incomplete mixture of material from two carbon-rich chondritic reservoirs, one (Mg-rich) with reduced iron, low Δ¹⁷O and low δ¹³C, and the other with oxidised iron, high Δ¹⁷O and high δ¹³C. Here we analyse noble gases (Ar, Kr and Xe) in six equilibrated (unbrecciated) ureilites from Northwest Africa (NWA 2236, NWA 7686, NWA 8049, NWA 8172, NWA 11032 and NWA 11368). We observe weak positive and negative correlations of Δ¹⁷O and Mg# with the elemental ratios of Ar/Xe and Kr/Xe, respectively, as well as a weak positive correlation of Mg# with the heavy isotopes of Xe. These correlations broadly support the idea of the two-component mixing hypothesis. Our analyses further suggest that the Mg-rich endmember was rich in Xe from presolar grains (HL-Xe) while the Mg-poorer component may have contained solar-derived noble gases. The observed correlations are less straightforward to reconcile with a recent model for the origin of the ureilite parent body, involving oxidation of metal by H₂O from accreted ice with ‘heavy’ oxygen isotopes.

¹Ryan C.Ogliore,²Russell L.Palma,³ Julien Stodolna,⁴Kazuhide Nagashima,⁵Robert O.Pepin,⁵ D.J.Schlutter,⁶Zack Gainsforth,⁶Andrew J.Westphal,⁴Gary R.Huss
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.11.033]
¹Department of Physics, Washington University in St. Louis, St. Louis, MO 63130
²Minnesota State University – Mankato
³EDF Lab les Renardiéres 77818 Moret Sur Loing France
⁴Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, HI 96822
⁵University of Minnesota – Twin Cities
⁶Space Sciences Laboratory, University of California at Berkeley
Copyright Elsevier

We report the structure, chemical composition, O, Al-Mg, He, and Ne isotope systematics of an interplanetary dust particle, “Manchanito”. These analyses indicate that Manchanito solidified as refractory glass (with oxidized Fe but reduced Ti) in a chondrule-like formation environment more than 3.2 Myr after CAIs, after which it was exposed to Q-like noble gases in the dissipating solar nebula. Manchanito’s He and Ne isotopic composition and concentrations are similar to those measured in samples of comet Wild 2, from which we infer that Manchanito’s parent body was a comet. We propose that after formation and exposure to Q-like gases, Manchanito was transported to the outer Solar System where it came into contact with organics and volatile ices on its cometary parent body. Manchanito provides additional evidence that cometary solids have been subjected to energetic processing and large-scale transport in a wide range of environments in the Solar System.