EFFECT OF DEFORMATION ON OXYGEN-ISOTOPE EXCHANGE IN THE HEAVITREE QUARTZITE, RUBY-GAP DUPLEX, CENTRAL AUSTRALIA

delta(18)O values of the Heavitree Quartzite, central Australia, vary systematically as a function of deformation and recrystallization in a duplex composed of 5 superposed thrust sheets which formed under gree nschist-grade conditions. Undeformed quartzite of the basal thrust she et 1 and moderately strained and partially recrystallized quartzite of thrust sheet 2 range over 4 parts per thousand in delta(18)O values a nd have an average value of similar to 12.8 parts per thousand. Entire ly recrystallized quartzite of overlying thrust sheet 3 retains a simi lar average value of similar to 12.3 parts per thousand but shows a na rrow range of similar to 1.5 parts per thousand, suggesting isotopic h omogenization. Recrystallized quartzites of sheet 5 have a lower delta (18)O value than the other thrust sheets. The homogenized delta(18)O v alues of sheet 3 relative to sheets 1 and 2 could not have resulted fr om mechanical mixing, isotopic exchange during dissolution-reprecipita tion, or exchange by diffusion between the quartzite and a fluid in mi crofractures or along grain boundaries. The homogenized delta(18)O val ues of sheet 3 and lowered values of sheet 5 are interpreted to have b een produced by isotopic exchange during recrystallization by grain-bo undary migration. This is probably an important mechanism of isotopic exchange for rocks undergoing dynamic recrystallization.