Alteration of CAIs as recorded by 36S/34S as a function of 35Cl/34S

I. Leya, J. Masarik, Y. Lin

Meteoritics & Planetary Science
First published: 25 March 2018


“Using new model calculations, we study the production of chlorine and sulfur isotopes in different irradiation scenarios. We demonstrate that irradiation during meteorite transit from the asteroid belt to Earth has a negligible influence on the sulfur isotopic composition. We analyzed five different physical assemblages: carbonaceous chondrites, carbonaceous chondrites covered with water ice, carbonaceous chondrites covered with water ice that contains silicates and chlorine, precursor CAIs, and water ice that contains chlorine. For each of these five we ran simulations in which they were irradiated by galactic cosmic rays or solar energetic particles. We found that for producing sufficient amounts of 36Cl, the required GCR and SEP flux densities must have been either unreasonably high on absolute terms or must had been high relatively late after the formation of the solar system. This finding casts doubt on the interpretation of the correlation lines in the diagram 36S/34S and 35Cl/34S as isochrons. Alternatively, the correlation may be interpreted as mixing between water that contains chlorine that has been irradiated (likely as ice) either by GCR or SEP particles and sulfur (without any chlorine) with solar isotopic composition. Using this model we can explain the correlation as mixing between components, one of which was exposed to energetic particles; the conditions of this irradiation are not unrealistic. “