Journal
EARTH AND PLANETARY SCIENCE LETTERS
Volume 408, Issue -, Pages 171-182Publisher
ELSEVIER
DOI: 10.1016/j.epsl.2014.10.013
Keywords
thermochronology; continental lithosphere; diffusion; U-Pb; rutile
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Funding
- Jackson Postdoctoral Fellowship
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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 Pb-206/U-238 age and trace element profiles from U-bearing accessory phases. Inversion of Pb-206/U-238 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 Pb-206/U-238 age and Zr diffusion profiles in the outer similar to 35 mu m of lower-crustal rutile euhedra from the Ivrea Zone, Southern Alps, with <1.2 mu m depth resolution. Inversion of the age profiles reveals a continuous cooling history characterized by initially rapid cooling from >600 degrees C at similar to 180 Ma followed by a period of slower cooling from similar to 525 degrees C to 450 degrees 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 Pb-206/U-238 age distributions can be employed to resolve otherwise inaccessible thermal history information from the lower lithosphere. (C) 2014 Elsevier B.V. All rights reserved.
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