Short lived ^(36)Cl and its decay products ^(36)Ar and ^(36)S in the early solar system

Variable excesses of ^(36)S have previously been reported in sodalite in the Allende and Ningqiang meteorites and used to infer the presence of ^(36)Cl in the early solar system. Until now no unambiguous evidence of the major decay product, ^(36)Ar (98%), has been found. Using low fluence fast neutron activation we have measured small amounts of ^(36)Ar in the Allende sodalite Pink Angel, corresponding to ^(36)Cl/^(35)Cl = (1.9 ± 0.5) × 10^(−8). This is a factor of 200 lower than the highest value inferred from ^(36)S excesses in sodalite. High resolution I–Xe analyses confirm that the sodalite formed between 4561 and 4558 Ma ago. The core of Pink Angel sodalite yielded a precise formation age of 4559.4 ± 0.6 Ma. Deposition of sodalite containing live ^(36)Cl, seven million years or so after the formation of the CAI, appears to require a local production mechanism involving intense neutron irradiation within the solar nebula. The constraint imposed by the near absence of neutron induced ^(128)Xe is most easily satisfied if the ^(36)Cl were produced in a fluid precursor of the sodalite. The low level of ^(36)Ar could be accounted for as a result of residual in-situ ^(36)Cl decay, up to 1–2 Ma after formation of the sodalite, and/or later diffusive loss, in line with the low activation energy for Ar diffusion in sodalite.