¹Ko Hashizume et al. (>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14175]
¹Faculty of Science, Ibaraki University, Mito, Japan
Published by arrangement with John Wiley & Sons

The nitrogen isotope compositions of two samples returned from the asteroid Ryugu were determined using a stepwise combustion method, along with Ivuna (CI) and Y-980115, a CI-like Antarctic meteorite, as references. The two Ryugu samples A0105-07 and C0106-07 showed bulk δ15N values of +1.7 ± 0.5‰ and +0.2 ± 0.6‰, respectively, significantly lower than Ivuna with +36.4 ± 0.4‰, but close to Y-980115 with +4.0 ± 0.3‰. The Ryugu samples are further characterized by C/N and 36Ar/N ratios up to 3.4× and 4.9× the value of Ivuna, respectively. Among all Ryugu samples and CI chondrites, a positive correlation was observed between nitrogen concentrations and δ15N values, with samples with lower nitrogen concentrations exhibiting lower δ15N. This trend is explained by a two-component mixing model. One component is present at a constant abundance among all CI-related samples, with a δ15N value around 0‰ or lower. The other varies in abundance between different samples, and exhibits a δ15N value of +56 ± 4‰. The first 15N-poor endmember is seemingly tightly incorporated into a carbonaceous host phase, whereas the 15N-rich endmember can be mobilized and decoupled from carbon, potentially because it is in the form of ammonia. Asteroid materials with volatile compositions that are similar to those reported here for the Ryugu samples are attractive candidates for the volatile sources among Earth’s building blocks.

^1,2Maree McGregor,^1,2John G. Spray,²Christopher R. M. McFarlane
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14172]
¹Planetary and Space Science Centre, University of New Brunswick, Fredericton, New Brunswick, Canada
²Department of Earth Sciences, University of New Brunswick, Fredericton, New Brunswick, Canada
Published by arrangement with John Wiley & Sons

In situ LA-ICP-MS/MS U-Pb and Rb-Sr geochronology combined with geochemical analysis and electron microscopy have been performed on ejecta components sampled from the Mid-to-Late Triassic Mercia Mudstone Group at Churchwood Quarry, SW England. The layer comprises altered impact spherules, melt-rich and fragment-rich accreted grain clusters (AGCs), along with shocked mineral phases. Late Triassic ages are obtained: a U-Pb age of 219 ± 72 Ma from variably shock-metamorphosed apatite and a Rb-Sr age of 213 ± 31 Ma from melt-rich AGCs. A post-depositional U-Pb age of 200 ± 7.5 Ma obtained from the carbonate host matrix correlates with an early Jurassic dolomitization event associated with regional marine transgression. Several links to the Manicouagan impact structure, Canada, are identified that complement previous provenance studies: (1) rare earth element compositions of impact spherules and melt-rich AGCs match those of the Manicouagan impact melt sheet; (2) the preservation of Archean and Paleo- to Neoproterozoic target rock U-Pb ages in zircon and apatite match those recorded within Manicouagan basement lithologies; and (3) impact spherules and melt-rich AGCs record initial 87Sr/86Sr compositions that overlap with those of the Manicouagan impact melt sheet and the target rocks involved in their generation.