Solubility of noble gases in serpentine: implications for meteoritic noble gas abundances

Experiments to study the incorporation of noble gases during synthesis of serpentine and during equilibration of serpentine with the atmosphere are reported. Hydrothermal synthesis and exchange experiments were conducted at 3400C and 1 kbar with partial pressures of noble gases from 2 X 10-8 to 10-1 atm. Exchange experiments were also conducted with the terrestrial atmosphere at lower temperatures. The values of the measured distribution coefficients (cm3 STP/g atm) for noble gases are not sufficiently high to account for the trapped noble gases in carbonaceous chondrites by exchange in the solar nebula if meteoritic minerals have comparable distribution coefficients. Of additional significance is the fact that serpentine gains and loses noble gases to approach equilibrium solubility values with the terrestrial atmosphere. Consequently exposure to the terrestrial atmosphere may have influenced the noble gas abundances in phyllosilicate minerals of carbonaceous chondrites. The dispersion of K-Ar ages of carbonaceous chondrites could be the result of phyllosilicate minerals approaching equilibrium solubility of atmospheric 40Ar. (Auth.)