^1,2Prajkta Mane,³Shawn Wallace,²Maitrayee Bose,¹Paul Wallace,²Meenakshi Wadhwa,¹Juliane Weber,^1,4Thomas J.Zega
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.06.006]
¹Lunar and Planetary Laboratory, University of Arizona, 85721, Tucson, AZ, USA
²School of Earth and Space Exploration, Arizona State University, 87287, Tempe, AZ, USA
³EDAX, Ametek, Materials Analysis Division, 07430, Mahwah, USA
⁴Dept. of Materials Science and Engineering, University of Arizona, 85721, Tucson, USA
Copyright Elsevier

Calcium-aluminum-rich inclusions (CAIs) and chondrules are among the most predominant chondritic components contained within primitive meteorites. As CAIs are the first solids to form in the solar nebula, they contain a record of its earliest chemical and physical processes. Here we combine electron backscatter diffraction (EBSD) and 26Al-26Mg chronology techniques to determine the crystallographic properties and ages of CAI components that provide temporal as well as spatial constraints on their origins and subsequent processing in the solar protoplanetary disk. We find evidence of shock deformation within a CAI, suggesting that it was deformed as a free-floating object soon after the CAI formation at the beginning of the Solar System. Our results suggest that even though CAIs and chondrules formed in distinct environments and on different timescales, they were likely affected by similar shock processes that operated over large temporal (0 to ∼4 Ma) and spatial (0.2 to at least 2 to 3 au) extents. Our results imply that nebular shock events were active on a wider scale in the solar protoplanetary disk than previously recognized.

¹Gatien L.F.Morin,¹Yves Marrocchi,¹Johan Villeneuve,²Emmanuel Jacquet
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.06.017]
¹Université de Lorraine, CNRS, CRPG UMR 7358, Vandoeuvre-lès-Nancy, 54501, France
²IMPMC, CNRS & Muséum national d’Histoire naturelle, UMR 7590, CP52, 57 rue Cuvier, 75005 Paris, France
Copyright Elsevier

CI chondrites have nonvolatile chemical compositions closely resembling that of the Sun’s photosphere and are thus considered to have the most primitive compositions of all known solar system materials. They have, however, experienced pervasive parent-body alteration processes that transformed their primary constituents, obscuring the nature and origin of primordial CI dust. We used in-situ quantitative microprobe and secondary ion mass spectrometry techniques to characterize the chemistry and oxygen isotopic compositions of anhydrous silicates in two sections of the CI chondrites Ivuna and Alais, which contain higher abundances of those than other CI samples. These silicates are Mg-rich olivine and low-Ca pyroxene crystals mostly occurring as aggregates within sub-mm Fe-rich clasts. Our data reveal mass-independent oxygen isotopic variations with Δ17O values ranging from −23.63 to −0.57‰, representing the first evidence of extremely 16O-rich (Δ17O < −20‰) olivine and pyroxene grains in CI chondrites. Two of these olivines are characterized by MnO/FeO ∼ 1, typical of low-iron, Mn-enriched silicates commonly observed in amoeboid olivine aggregates. Other anhydrous silicate grains have Δ17O values ranging from −6 to 0‰, probably representing chondrule fragments. Combined, these results indicate that chondrule and refractory inclusion material were incorporated into the CI parent body(ies). This conclusion is consistent with recent models showing that refractory inclusions could have formed and/or been transported at larger heliocentric distances than previously thought during the concomitant injection of material from the molecular cloud and outward extension of the disk by viscous spreading. The CI chondrules are presumably of local origin, with their isotopic systematics suggesting an affinity with the CR clan.