Primordial heavy noble gases in the pristine Paris carbonaceous chondrite

Abstract

The Paris carbonaceous chondrite represents the most pristine carbonaceous chondrite, providing a unique opportunity to investigate the composition of early solar system materials prior to the onset of significant aqueous alteration. A dual origin (namely from the inner and outer solar system) has been demonstrated for water in the Paris meteorite parent body (Piani et al. 2018 ). Here, we aim to evaluate the contribution of outer solar system (cometary‐like) water ice to the inner solar system water ice using Xe isotopes. We report Ar, Kr, and high‐precision Xe isotopic measurements within bulk CM 2.9 and CM 2.7 fragments, as well as Ne, Ar, Kr, and Xe isotope compositions of the insoluble organic matter ( IOM ). Noble gas signatures are similar to chondritic phase Q with no evidence for a cometary‐like Xe component. Small excesses in the heavy Xe isotopes relative to phase Q within bulk samples are attributed to contributions from presolar materials. CM 2.7 fragments have lower Ar/Xe relative to more pristine CM 2.9 fragments, with no systematic difference in Xe contents. We conclude that Kr and Xe were little affected by aqueous alteration, in agreement with (1) minor degrees of alteration and (2) no significant differences in the chemical signature of organic matter in CM 2.7 and CM 2.9 areas (Vinogradoff et al. 2017 ). Xenon contents in the IOM are larger than previously published data of Xe in chondritic IOM , in line with the Xe component in Paris being pristine and preserved from Xe loss during aqueous alteration/thermal metamorphism.

The origin and fate of volatile elements on Earth revisited in light of noble gas data obtained from comet 67P/Churyumov-Gerasimenko

“…The Kr and Xe signatures measured in comet 67P/C-G define a nucleosynthetic component that is unique within our solar system, with notable depletions in 83 Kr, 86 Kr, 134 Xe and 136 Xe relative to the "normal" (N) composition 12,31 . The Kr isotopic signature of comet 67 P/C-G would be best accounted for by a mix of presolar N-Kr plus 2-5% G-Kr 31,87 (Fig.…”

“…A possibility is that the noble gas signature of comet 67P/C-G represents the composition of the outer solar system/interstellar reservoir from which comets originally formed 12 and therefore, the noble gas signature of comets having accreted from the same region as comet 67P/C-G should reflect a similar nucleosynthetic mixture. In this framework, it is however surprising that no evidence for a cometary noble gas contribution to the CC reservoir (especially Xe) could be found so far 86 .…”

“…S2). This may in part explain why the addition of comet 67P/C-G to a chondritic atmosphere does not succeed in exactly reproducing the 83 Kr/ 86 Kr signature of the atmosphere (Fig. S1).…”

“…This suggests that (i) comets may have also contributed significant quantities of Kr to the atmosphere and (ii) cometary noble gases were predominantly mixed with chondritic -and not solar -sources to form the atmosphere 12 . However, as discussed in the "working hypotheses: Pros and Cons" section entitled ", the addition of cometary Kr to a chondritic atmosphere does not succeed in exactly reproducing the 83 Kr/ 86 Kr signature of the atmosphere (Fig. S1), which could be accounted for by the extreme isotopic variability of the comet nucleosynthetic precursors (Fig.…”

Testing the genetic relationship between fluid alteration and brecciation in CM chondrites

“…CM-like matter also represents a significant fraction of exogenic clasts in other groups of meteorites, suggesting that their parent bodies are widespread in the asteroid belt Gounelle et al 2005;Bischoff et al 2006;Briani et al 2012). To a few exceptions, like the Y-791198 and Paris meteorites (Chizmadia and Brearley 2008;Hewins et al 2014;Vacher et al 2016), all CM chondrites are described as impact/regolith breccias (Bischoff et al 2006), as they contain solar-wind-implanted rare gases and have clastic matrices consistent with a near-surface origin on their parent body (Greenwood et al 1993;Nakamura et al 1999;Bekaert et al 2019). Although they are categorized as lightly shocked (Scott et al 1992), their chondrules, isolated anhydrous minerals, and matrix phyllosilicates often display foliation features consistent with multiple hypervelocity impacts (Rubin 2012;Hanna et al 2015;Lindgren et al 2015;Vacher et al 2018).…”