Vapour Fractionation and K/Rb Ratios of Melt Phases in the Onaping Formation Sudbury, Ontario

Abstract

<p> The process of vapour fractionation during impact fusion of country rocks is discussed in relation to absolute loss and relative loss. The factors which determine the amount of vapour fractionation are considered in an equilibrium thermodynamic model. The model is tested upon the relative vapour fractionation of Rb with respect to K. Application of the model to crater studies leads to sampling concepts and the statistical validity of differences in measured compositions of melt rock and adjacent country rocks.</p> <p> The petrography and K/Rb ratios of twelve samples of melt phases in the Onaping formation, Sudbury, Ontario are presented. The data is discussed in the light of theoretical model for vapour fractionation.</p>