¹Simone Gerber, ¹Christoph Burkhardt, ¹Gerrit Budde, ¹Knut Metzler, ¹Thorsten Kleine
The Astrophysical Journal Letters 841 L17 Link to Article [https://doi.org/10.3847/2041-8213/aa72a2]
¹Institut für Planetologie, University of Münster, Wilhelm Klemm-Straße 10, D-48149 Münster, Germany

Chondrules formed by the melting of dust aggregates in the solar protoplanetary disk and as such provide unique insights into how solid material was transported and mixed within the disk. Here, we show that chondrules from enstatite and ordinary chondrites show only small 50Ti variations and scatter closely around the 50Ti composition of their host chondrites. By contrast, chondrules from carbonaceous chondrites have highly variable 50Ti compositions, which, relative to the terrestrial standard, range from the small 50Ti deficits measured for enstatite and ordinary chondrite chondrules to the large 50Ti excesses known from Ca–Al-rich inclusions (CAIs). These 50Ti variations can be attributed to the addition of isotopically heterogeneous CAI-like material to enstatite and ordinary chondrite-like chondrule precursors. The new Ti isotopic data demonstrate that isotopic variations among carbonaceous chondrite chondrules do not require formation over a wide range of orbital distances, but can instead be fully accounted for by the incorporation of isotopically anomalous “nuggets” into chondrule precursors. As such, these data obviate the need for disk-wide transport of chondrules prior to chondrite parent body accretion and are consistent with formation of chondrules from a given chondrite group in localized regions of the disk. Finally, the ubiquitous presence of 50Ti-enriched material in carbonaceous chondrites and the lack of this material in the non-carbonaceous chondrites support the idea that these two meteorite groups derive from areas of the disk that remained isolated from each other, probably through the formation of Jupiter.

^1,2,3,4Pierre Haenecour, ^1,3Christine Floss, ⁴Thomas J. Zega, ^1,3Thomas K. Croat, ^2,3Alian Wang, ^2,3Bradley L. Jolliff, ^2,3Paul Carpenter
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.06.004]
¹Laboratory for Space Sciences and Physics Department, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130-4899, USA
²Department of Earth and Planetary Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130-4899, USA
³McDonnell Center for the Space Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130-4899, USA
⁴Lunar and Planetary Laboratory and Department of Materials Science and Engineering, University of Arizona, 1629 E. University Blvd, Tucson, AZ 85721-0092, USA
Copyright Elsevier

To investigate the origin of fine-grained rims around chondrules (FGRs), we compared presolar grain abundances, elemental compositions and mineralogies in fine-grained interstitial matrix material and individual FGRs in the primitive CO3.0 chondrites Allan Hills A77307, LaPaz Icefield 031117 and Dominion Range 08006. The observation of similar overall O-anomalous (∼155 ppm) and C-anomalous grain abundances (∼40 ppm) in all three CO3.0 chondrites suggests that they all accreted from a nebular reservoir with similar presolar grain abundances. The presence of presolar silicate grains in FGRs combined with the observation of similar estimated porosity between interstitial matrix regions and FGRs in LAP 031117 and ALHA77307, as well as the identification of a composite FGR (a small rimmed chondrule within a larger chondrule rim) in ALHA77307, all provide evidence for a formation of FGRs by accretion of dust grains onto freely-floating chondrules in the solar nebula before their aggregation into their parent body asteroids. Our study also shows systematically lower abundances of presolar silicate grains in the FGRs than in the matrix regions of CO3 chondrites, while the abundances of SiC grains are the same in all areas, within errors. This trend differs from CR2 chondrites in which the presolar silicate abundances are higher in the FGRs than in the matrix, but similar to each other within 2σ errors. This observation combined with the identification of localized (micrometer-scaled) aqueous alteration in a FGR of LAP 031117 suggests that the lower abundance of presolar silicates in FGRs reflects pre-accretionary aqueous alteration of the fine-grained material in the FGRs. This pre-accretionary alteration could be due to either hydration and heating of freely floating rimmed chondrules in icy regions of the solar nebula or melted water ice associated with 26Al-related heating inside precursor planetesimals, followed by aggregation of FGRs into the CO chondrite parent-body.

^1,2,3,4Adam R. Sarafian, ^1,4Sune G. Nielsen, ^1,5Horst R. Marschall, ¹Glenn A. Gaetani, ⁶Erik H. Hauri, ⁷Kevin Righter, ^2,3Emily Sarafian
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.06.001]
¹Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02540
²Massachusetts Institute of Technology-Woods Hole Oceanographic Institution Joint Program in Oceanography/Applied Ocean Science and Engineering, Cambridge, MA 02139
³Geology and Geophysics Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543
⁴NIRVANA Laboratories, Woods Hole Oceanographic Institution, Woods Hole, MA 02540, USA
⁵Institut für Geowissenschaften, Goethe Universität Frankfurt, Altenhöferallee 1, 60438 Frankfurt am Main, Germany
⁶Carnegie Institution for Science, Department of Terrestrial Magnetism, Washington, DC 20015
⁷NASA Johnson Space Center, 2101 NASA Parkway, Houston, TX 77058
Copyright Elsevier

Earth and the other rocky bodies that make up the inner solar system are systematically depleted in hydrogen (H) and other cosmochemically volatile elements (e.g., carbon (C), fluorine (F), chlorine (Cl), and thallium (Tl)) relative to primitive undifferentiated meteorites known as carbonaceous chondrites. If we are to understand how and when Earth gained its life-essential elements, it is critical to determine the timing, flux, and nature of the delivery of condensed volatiles into the presumed hot and dry early inner solar system. Here we present evidence preserved in ancient basaltic angrite meteorites for an addition of volatiles to the hot and dry inner solar system within the first two million years of solar system history. Our data demonstrate that the angrite parent body was enriched in highly volatile elements (H, C, F, and Tl) relative to those predicted on the basis of the angrite parent body’s overall volatile depletion trend (e.g., H is enriched by up to a factor of 106).This relative enrichment is best explained by mixing of extremely volatile-depleted material, located well inside the snow line, with volatile-rich material derived from outside the snow line.