Argon diffusion in glauconite, microcline, sanidine, leucite and phlogopite

Abstract

Data on the diffusion of Ar in sanidine, microcline, phlogopite, glauconite, and leucite are presented. We conclude from these data that: 1) Dynamic lattice changes markedly influence Ar loss at the time of the changes. 2) If Ar diffusion takes place under conditions of no lattice changes, all Ar will be lost at a single activation energy. 3) Glauconite and phlogopite have essentially identical diffusion characteristics. 4) The parameters of the diffusion equations for both feldspar and mica are only explainable on an hypothesis of extreme ordering of the diffusing Ar atoms. 5) Glauconites (and illites), due to their fine grain-size, are susceptible to high Ar loss at a temperature of 100 degrees C. if that temperature is maintained for a few million years. Thus, knowledge of the burial history of a sample is absolutely essential for each glauconite dated. 6) Feldspar diffusion appears to be a complex of lattice and grain-boundary diffusion, with the lattice unit having dimensions of 10-30 microns. 7) Heating a mica of 1 mm. thickness to 300 degrees C. for a few million years should remove all preexisting Ar, thus rendering impossible the dating of events prior to the last heating.