^1,2Y. Boleaga,^2,3,4M. K. Weisberg,^4,5J. M. Friedrich,^3,4D. S. Ebel
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13762]
¹City College, City University of New York, New York, New York, 10031 USA
²Department of Physical Sciences, Kingsborough College CUNY, Brooklyn, New York, 11235 USA
³Department of Earth and Environmental Science, CUNY Graduate Center, New York, New York, 10016 USA
⁴Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, 10024 USA
⁵Department of Chemistry, Fordham University, Bronx, New York, 10458 USA
Published by arrangement with John Wiley & Sons

We present the results of our study of two thin sections of Pecora Escarpment (PCA) 91020, a heavily shocked EL3 chondrite, to characterize the sizes, shapes, orientations, and mineral compositions of its chondrules and opaque nodules. We also studied the mildly shocked Queen Alexandra Range (QUE) 94594 EL3 chondrite for comparison. PCA 91020 appears to show the evidence of deformation throughout the meteorite in both the chondrules and the opaque (metal–sulfide) nodules. Aspect ratios of the chondrules in PCA 91020 are greater than in the mildly shocked QUE 94594. Aspect ratios of the more ductile metal grains are higher than those of the chondrules in both sections of PCA 91020 and in QUE 94594. The data suggest that the chondrules and metal-rich nodules in PCA 91020 were elongated (flattened) to a greater degree and show a preferred orientation in comparison to objects in typical EL3 chondrites such as QUE 94594. The chondrule and metal-rich nodule deformation and foliation in PCA 91020 were likely produced by an impact on the EL3 asteroid. However, there are some inconsistencies in reconciling an impact hypothesis with all of the observations. Scenarios of hot accretion and/or overburden compaction during progressive (potentially rapid, hot) accretion to explain the deformation cannot be completely ruled out. Also, heavily shocked E3 chondrites, like PCA 91020, are relatively rare, suggesting the impacts that may have compacted chondrites, although potentially frequent, were of weak magnitude.

¹Nan Liu,²Nicolas Dauphas,^3,4Sergio Cristallo,^4,5Sara Palmerini,^4,5Maurizio Busso
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.11.022]
¹Department of Physics, Washington University in St. Louis, MO 63130, USA
²Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, IL 60637, USA
³INAF, Osservatorio Astronomico d’Abruzzo, Via Mentore Maggini snc, 64100 Teramo, Italy
⁴INFN, Sezione di Perugia, Via A. Pascoli snc, 06123 Perugia, Italy
⁵Department of Physics and Geology, University of Perugia, Via A. Pascoli snc, I-06123 Perugia, Italy
Copyright Elsevier

Presolar oxide grains have been previously divided into several groups (Group 1 to 4) based on their isotopic compositions, which can be tied to several stellar sources. Much of available data was acquired on large grains, which may not be fully representative of the presolar grain population present in meteorites. We present here new O isotopic data for 74 small presolar oxide grains (∼200 nm in diameter on average) from Orgueil and Al-Mg isotopic systematics for 25 of the grains. Based on data-model comparisons, we show that (i) Group 1 and Group 2 grains more likely originated in low-mass first-ascent (red giant branch; RGB) and/or second-ascent (asymptotic giant branch; AGB) red giant stars and (ii) Group 1 grains with (26Al/27Al)0 ⪆ 5×10−3 and Group 2 grains with (26Al/27Al)0 ⪅ 1×10−2 all likely experienced extra circulation processes in their parent low-mass stars but under different conditions, resulting in proton-capture reactions occurring at enhanced temperatures. We do not find any large 25Mg excess in Group 1 oxide grains with large 17O enrichments, which provides evidence that 25Mg is not abundantly produced in low-mass stars. We also find that our samples contain a larger proportion of Group 4 grains than so far suggested in the literature for larger presolar oxide grains (≥ 400 nm). We also discuss our observations in the light of stellar dust production mechanisms.