Understanding of the thermal and geophysical evolution of the lower continental crust is limited by the resolution of conventional thermochronology. Intracrystalline daughter nuclide distribution profiles preserve a rich and underutilized record of thermal history. Using Laser Ablation Inductively Coupled Plasma Mass Spectrometry, we outline here a method to simultaneously acquire 206Pb/238U age and trace element profiles from U-bearing accessory phases. Inversion of 206Pb/238U age depth profiles yields thermal history information from an extended temperature range compared to inversion of age versus grain size relationships. Thermally-activated volume diffusion of Pb and Zr in rutile is sensitive to the thermal evolution of the mid- to lower-lithosphere. We document the ability of Laser Ablation depth-profiling to simultaneously resolve 206Pb/238U age and Zr diffusion profiles in the outer ~35μm of lower-crustal rutile euhedra from the Ivrea Zone, Southern Alps, with <1.2μm depth resolution. Inversion of the age profiles reveals a continuous cooling history characterized by initially rapid cooling from >600°C at ~180Ma followed by a period of slower cooling from ~525°C to ~450°C. Combined with the topology of Zr diffusion profiles, these data indicate that the Ivrea Zone underwent a brief thermal pulse in the early Jurassic, plausibly associated with hyperextension of the Adriatic margin. Inversion of near-surface 206Pb/238U age distributions can be employed to resolve otherwise inaccessible thermal history information from the lower lithosphere.
All Science Journal Classification (ASJC) codes
- Geochemistry and Petrology
- Earth and Planetary Sciences (miscellaneous)
- Space and Planetary Science