Oxygen and hydrogen isotopic compositions of coexistent minerals of the Tasigake alkali granite pluton, northern Xinjiang: constraints upon the cause of ~(18)O-D depletion and the ~(18)O/~(16)O exchange kinetics

Oxygen and hydrogen isotopic compositions have been determined of three coexistent mineral triplets of alkali feldspar, quartz, arfvedsonite of 11 samples collected from the Tasigake alkali granite pluton, Ulungur River region, northern Xinjiang. Isotopic exchange with meteoric water during subsolidus cooling caused strong18O-D depletion and the remarkable nonequilibrium18O/16O relation between coexistent minerals.18O/16O exchange kinetic effects of the three minerals are simultaneously and consistently modelled. Exsolution and microtextural reorganization of alkali feldspar, and infiltration of water have been mutually facilitated by each other. Shallow intrusion, and circulation of meteoric water throughout the pluton cool it effectively. As a result, the “heat engine” is rapidly extinguished, and the nonequilibrium18O/16O relation is frosen.