OXYGEN ISOTOPE FRACTIONATION BETWEEN HOST AND EXSOLVED PHASES IN PERTHITE

Oxygen isotope analyses of exsolved plagioclases and host microcline from three granitic perthites show no significant differences between host and exsolved phase. This is in agreement with the hypothesis of exsolution by alkali ion diffusion alone. However, the precision of analysis is insufficient to rule out reconstruction of the feldspar lattice and equilibration between Na-rich and K-rich phases during exsolution.