HF-ZR INTERDIFFUSION IN SINGLE-CRYSTAL ZIRCON .2. DETERMINATION BY BACKSCATTERED ELECTRON IMAGE

Hf-Zr interdiffusivity in zircon has been determined on hafnon-zircon double-layered crystals using back-scattered electron image contrast in a scanning electron microscope. The observed Hf-Zr interdiffusion coefficient at 1600-degrees-C and 1500-degrees-C in the direction perpendicular to the c-axis is 2 x 10(-15) and 3 x 10(-16) cm2/sec, respectively. The value observed at 1600-degrees-C perpendicular to the c-axis is about an order of magnitude higher compared with the value of approximately 2 x 10(-16) cm2/sec along the c-axis. These observed low diffusivity values suggest that diffusivities of Th and U in zircon are expected to be similarly low.