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

Variable excesses of S-36 have previously been reported in sodalite in the Allende and Ningqiang meteorites and used to infer the presence of Cl-36 in the early solar system. Until now no unambiguous evidence of the major decay product, Ar-36 (98%), has been found. Using low fluence fast neutron activation we have measured small amounts of Ar-36 in the Allende sodalite Pink Angel, corresponding to Cl-36/Cl-35 = (1.9 + 0.5) x 10(-8). This is a factor of 200 lower than the highest value inferred from S-36 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 Cl-36, 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 Cl-36 were produced in a fluid precursor of the sodalite. The low level of Ar-36 could be accounted for as a result of residual in-situ Cl-36 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. (C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved.