TRAPPED NEON IN METEORITES .2.

Studies of the structure of trapped meteoritic neon are continued through stepwise heating experiments on carbonaceous chondrites and gas-rich meteorites. Trapped 20Ne 22Ne ratios are observed to vary by more than a factor 4, from extremes of 3.4-4.8 in 1000°C gas fractions from six carbonaceous chondrites to ∼14 in neon evolved from Kapoeta at very low temperatures. The description of trapped neon in meteorites as a variable mixture of two components with 20Ne 22Ne= 8.2 (Neon-A) and 12.5 (Neon-B) is qualitatively valid for total neon, but it cannot account for the extreme compositions revealed in these individual temperature fractions. At least two other components, with 20Ne 22Ne ≲ 3.4 and ≳ 14, are required. The 20Ne/22Ne ratio in Neon-B is very close to 12.5 in all four of the gas-rich meteorites examined here. Evidence is presented for a third major neon component, 20Ne/22Ne = 11.2 in all carbonaceous chondrites and in most of the gas-rich meteorites. There is no firm evidence that any of these components originate from in situ mixing. There is no sign that diffusive fractionation is responsible for any of the isotopic variations. The great range of the variations effectively eliminates volume diffusion alone as a feasible mechanism. Suggestions for the origin of the component with 20Ne 22Ne ≲ 3.4 in nucleosynthesis or in a primitive irradiation are clearly speculative; the question is very much an open one. © 1969.