Diffusion of Pb was measured in natural and synthetic rutile under dry, 1atm conditions, using mixtures of Pb titanate or Pb sulfide and TiO2 as the sources of diffusant. Pb depth profiles were then measured with Rutherford back-scattering spectrometry. At 700 to 1100C, an Arrhenius relationship was obtained for the synthetic rutile:

D(m2/s) = 3.9 x 10-10exp[-250(kJ/mol)/RT]

The results for diffusion in natural and synthetic rutile were quite similar, despite significant differences in trace element compositions. Mean closure temperatures calculated from the diffusion parameters were around 600C for rutile grains of ~100μm size. This was about 100C higher than rutile closure temperature determinations from past field-based studies, suggesting that rutile was more resistant to Pb loss through volume diffusion than previously thought.

Pb Diffusion in Rutile. Cherniak, D.J.: Contributions to Mineralogy and Petrology, 2000, 139[2], 198-207