^1,2Shijie Li,³Ingo Leya,⁴Shijie Wang,^3,4Thomas Smith,^5,6Huiming Bao,^1,7Yan Fan,^1,2Bing Mo
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13710]
¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081 China
²Chinese Academy of Sciences Center for Excellence in Comparative Planetology, Hefei, China
³Physikalisches Institut, Universität Bern, Bern, 3012 Switzerland
⁴State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081 China
⁵Department of Geology and Geophysics, E235 Howe-Russell Geoscience Complex, Louisiana State University, Baton Rouge, Louisiana, 70803 USA
⁶International Center for Isotope Effects Research and School of Earth Sciences and Engineering, Nanjing University, Nanjing, 210023 China
⁷Department of Geology, Northwest University, Xi’an, 710069 China
Published by arrangement with John Wiley & Sons

Several hundred meteorites with a total mass of over 100 kg were collected as the Alatage Mountain (AM) strewn field located in the Kumtag desert, Xinjiang Province, China. Twelve AM meteorites were studied in this work. Petrography, mineralogy, bulk chemistry, bulk oxygen isotopic compositions, and light noble gas concentrations and isotopic compositions were determined for all or for a selection of the meteorites. The studied meteorites are L-chondrites that suffered a very strong impact; impact melt veins and melt pockets are widely distributed. More than 50% of the troilite exists in the form of blebs and veins in olivine and pyroxene. Some of these meteorites are impact melt recrystallized rocks (e.g., AM 037). The strong impact caused the decomposition of troilite, which led in AM 034 to the sulfidization reaction of olivine. The metal in most meteorites is almost completely altered, and the troilite has been significantly oxidized. Weathering resulted in the depletion of Mg, Fe, Co, and Ni, and the enrichment of Sr, Ba, Pb, and U in these meteorites. The cosmic ray exposure (CRE) ages measured for these specimens range between 6.2 ± 1.9 Ma and 9.0 ± 2.7 Ma, depending on the cosmogenic nuclide used. The average CRE age is 7.6 ± 1.3 Ma. Both 4He and 40Ar gas retention ages indicate that the strong impact which caused the shock effects occurred about 320 Ma ago.

¹S.A.Singerling,^2,3S.R.Sutton,³A.Lanzirotti,³M.Newville,¹A.J.Brearley
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.07.016]
¹Department of Earth and Planetary Sciences, MSC-03 2040 1 University of New Mexico, Albuquerque, NM 87131, USA
²Department of Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA
³Center for Advanced Radiation Sources, University of Chicago, Chicago, IL 60637, USA
Copyright Elsevier

We have performed a coordinated focused ion beam (FIB)-scanning and transmission electron microscopy (SEM, TEM), electron probe microanalysis (EMPA)-synchrotron X-ray fluorescence (SXRF) microprobe study to determine phase-specific microstructural characteristics and high-resolution in situ trace element concentrations of primary pyrrhotite, pentlandite, and associated metal grains from chondrules in CM2 and CR2 carbonaceous chondrites. This work is the first of its kind to link trace element chemical and microstructural observations in chondritic sulfides in an attempt to determine formation mechanisms and conditions of primary sulfides in these meteorite groups. SXRF and TEM analyses were performed on a small number of FIB sections which act as representative samplesof primary sulfides and associated metal present in pyrrhotite-pentlandite intergrowth (PPI) grains and sulfide-rimmed metal (SRM) grains.

SXRF microprobe analyses allowed the concentrations of the minor and trace elements, Co, Cu, Ge, Zn, and Se to be quantified, in addition to Fe and Ni, at a spatial resolution of 2 µm. The similarity between the CM and CR PPI sulfide trace element patterns provides evidence for a common formation mechanism for this type of sulfide grain in both meteorite groups. In addition, the SRM sulfide and metal have comparable trace element patterns that indicates a genetic relationship between the two, such as sulfidization of metal. Enrichments in Ni, Co, Cu, and Se are consistent with the chalcophile/siderophile behavior of these elements. The observed depletions in Ge suggest that it may have been lost by evaporation or else was never incorporated into the metal or sulfide precursor materials. The depletion in Zn may also be attributable to evaporation, but, being partially lithophile, may also have been preferentially incorporated into silicates during chondrule formation. Trace element concentrations support crystallization from an immiscible sulfide melt in chondrules for formation of the PPI grains and sulfidization of metal for the origin of the SRM grains.