¹George D. Cody, ¹Conel M. O’D. Alexander, ¹Dionysis I. Foustoukos, ^1,2Yoko Kebukawa, ¹Ying Wang
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.09.023]
¹Earth and Planets Laboratory, Carnegie Institution for Science, 5241 Broad Branch Road, NW, Washington, DC, United States
²Tokyo Institute of Technology, Department of Earth and Planetary Science, Tokyo, Japan
Copyright Elsevier

Rotationally resonant Deuterium Nuclear Magnetic Resonance spectroscopy (D MAS NMR) was applied to IOM isolated from a CR1 chondrite Grosvenor Mountains (GRO) 95577 and a CM2 chondrite (Murchison). It is shown that in IOM D strongly prefers the aliphatic hydrogen reservoir over the aromatic hydrogen reservoir. For GRO 95577, that has a bulk δD of 3303 ‰ (Alexander et al., 2010), the average δD value of the aromatic reservoir is 1740 ± 128 ‰ and the aliphatic reservoir is 4477 ± 105 ‰, i.e., D/H enrichments of 1.27 and 0.64, respectively, relative to the bulk. For Murchison IOM, that has a bulk δD of 811 ‰ (Alexander et al., 2010), the average δD of the aromatic reservoir is 512 ± 88 ‰ and the aliphatic reservoir is 1033 ± 64 ‰ i.e., D/H enrichments of 1.12 and 0.82, respectively, relative to the bulk. D-H exchange between D-enriched water and a type III kerogen reveals nearly equivalent D up take by both aromatics and aliphatics. Laboratory synthesis of IOM-like material in the presence of D2O reveals a high degree of deuteration with a strong preferential deuteration of the aliphatic hydrogen reservoir indicating that the δD of the water during IOM synthesis is the primary determinant of syn-IOM’s δD. The IOM in GRO 95577 and Murchison (FA and H/C × 100) lie on the molecular evolution line as defined by the IOM of the Tagish Lake clasts and Murchison IOM has experienced more molecular evolution relative to that exhibited by GRO 95577 IOM. A forward prediction derived from the D/H ratios for the aliphatic and aromatic hydrogen reservoirs in Murchison and GRO 95577, relative to their bulk D/H ratios, derived from D MAS NMR, is applied to explain the origin of the Tagish Lake trend of δD vs molecular evolution (H/C × 100). The results of this forward prediction suggest that the Tagish Lake isotopic trend results from a combination of molecular evolution (loss of predominantly aliphatic H and D) and partial D-H exchange with D depleted chondritic water during a short-term hydrothermal alteration event. Such events may be faithfully identified in chondritic organic solids and be a common occurrence, but not necessarily revealed in the mineralogy of type 1 and 2 carbonaceous chondrites.

¹Samuel Ebert, ²Kazuhide Nagashima, ²Alexander N. Krot, ³Shigeru Wakita, ⁴Jean-Alix Barrat, ¹Addi Bischoff
Earth and Planetary Science Letters 646, 119010, Open Access Link to Article [https://doi.org/10.1016/j.epsl.2024.119010]
¹Institut für Planetologie, University of Münster, D-48149, Münster, Germany
²Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA
³Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁴Institut Universitaire Européen de la Mer, Université de Bretagne Occidentale, Place Nicolas Copernic, F-29280, Plouzané Cedex, France
Copyright Elsevier

Calcium-aluminum-rich inclusions (CAIs) commonly observed in chondritic meteorites are the oldest dated solids formed in the Solar System. Short-lived isotope chronologies (²⁶Al-²⁶Mg, ¹⁸²Hf-¹⁸²W) suggest a ∼2 Ma gap between the formation of CAIs and the accretion of the final chondrite parent bodies. One thin section, 3.27 cm² in size, of an ordinary chondrite NWA 3358 (H3.1) studied contains 52 refractory inclusions (CAIs and amoeboid olivine aggregates (AOAs)) comprising 0.14 % of its area, which is the highest abundance of refractory inclusions among non-carbonaceous chondrites containing on average ∼0.009 area % of CAIs and AOAs. In combination with a low chondrule/matrix ratio of ∼1.5, this makes NWA 3358 a unique ordinary chondrite. The aqueously-formed fayalites (Fa_>99) in NWA 3358 have the inferred initial ⁵³Mn/⁵⁵Mn ratio of (5.56 ± 0.44) × 10⁻⁶ which is the highest measured value for secondary minerals in chondrites and corresponds to the formation time of ∼1.0–1.5 Ma after CAIs. Based on the ⁵³Mn-⁵³Cr chronology of fayalite formation and the thermal modeling, we infer that the first-generation of an H chondrite parent body, ∼6–12 km in diameter, accreted within 1.0 Ma after formation of CAIs, filling the gap of ∼2 Ma between CAIs and the earliest chondrite parent bodies. This early accretion provides a possible mechanism of CAIs/AOAs storage in the inner solar nebula and could explain the high amount of refractory inclusions in NWA 3358. A later destruction of these first-generation bodies may also explain the presence of CAIs and chondrules of different ages within later formed chondrite parent bodies.