Extracting thermal histories from the near-rim zoning in titanite using coupled U-Pb and trace-element depth profiles by single-shot laser-ablation split stream (SS-LASS) ICP-MS

• SS-LASS is a high-resolution technique for measuring chemical and isotopic zoning concurrently in the rims of titanite.
• Simultaneously collected U-Pb isotopic dates and Zr thermometry enables the calculation of thermal histories from the rims of zoned titanite.
• Simple 1D diffusion modeling of multiple element pairs with varying diffusivity allows for insight into mineral closure versus (re)crystallization in titanite
• Depth profiling and simple diffusion modeling of the near-rim zoning in titanites from the Pamir Plateau record (re)crystallization rather than diffusional modification.

A method for depth profiling using single-shot laser-ablation split stream (SS-LASS) ICP-MS is developed to simultaneously measure U-Pb age and trace-element concentrations in titanite. Simple semi-infinite, 1-D half-space diffusion models were applied to near-rim, trace-element zoned domains in titanite to distinguish between cooling and (re)crystallization ages and investigate the potential for preservation of thermally mediated diffusive loss profiles. These data illustrate the need to measure multiple trace elements with varying diffusivities to interpret a mineral's thermal history resulting from the non-unique nature of 1-D diffusion models where both temperature and time are unknown. A case study of titanites from two Pamir Plateau gneiss domes indicates they underwent ≥ 25 Myr of amphibolite and granulite facies metamorphism yet did not experience significant volume diffusion modification following (re)crystallization. The interpretation of prolonged (re)crystallization rather than diffusion allows for high-resolution, near-rim temperature-time histories to be extracted using U-Pb dates and Zr4 + apparent temperatures by SS-LASS.