Scientific Rationale: The precise and especially accurate measurement of geologic time continues to be one of most demanding requirements for deciphering a wide range of petrologic, tectonic, and paleobiologic problems. The "CA-TIMS" method of zircon U-Pb geochronology, a new method for high-resolution geochronology (Mattinson, 2005), already is yielding revolutionary improvements in precision and accuracy. We now need to better understand the physics and chemistry of CA-TIMS, in order to further refine it. One major goal of the proposal is detailed micron scale study of the inter-relationships among radiation damage, Pb loss, annealing, and zircon dissolution. The second major goal is understanding low-temperature fluid and radiation-damage mediated Pb loss in zircon, and its implications for both zircon geochronology and sequestration of radioactive waste in synthetic zircon or zircon-like materials. The third major goal is refining the decay constant of 235U, relative to 238U, using detailed, multi-step CA-TIMS on a carefully selected suite of natural zircon samples. Pilot studies will also be conducted on 231Pa disequilibrium effects, and on the significance of Pb redistribution in zircons by the alpha-recoil process.
Broader Impacts: One to two graduate students and two to three undergraduate students will be actively engaged in all aspects of the proposed research. A major part of the research will involve international collaboration, fostering closer ties with colleagues in Europe and Canada. The international geochronology community will benefit from CA-TIMS refinements. The UCSB zircon lab will be supported by the analytical budget.
