Development of the CA-TIMS method: Refining U-Pb Zircon Geochronology

科学原理：精确且特别准确的地质年代测量仍然是破译广泛的岩石学、构造和古生物学问题的最苛刻的要求之一。锆石U-Pb年代学的“CA-TIMS”方法是一种高分辨率年代学的新方法(Mattinson，2005)，它已经在精密度和准确度方面产生了革命性的改进。我们现在需要更好地了解CA-TIMs的物理和化学，以便进一步完善它。该提案的一个主要目标是详细研究辐射损伤、铅损失、退火和锆石溶解之间的相互关系。第二个主要目标是了解低温流体和辐射损伤导致的锆石中铅的损失，以及它对锆石年代学和放射性废物在合成锆石或类锆石材料中的封存的影响。第三个主要目标是在精心挑选的一套天然锆石样品上，使用详细的多步CA-TIM来精炼235U相对于238U的衰变常数。此外，还将就231Pa值的不平衡效应以及阿尔法反冲过程中铅在锆石中重新分布的意义进行初步研究。更广泛的影响：一到两名研究生和两到三名本科生将积极参与拟议研究的所有方面。这项研究的主要部分将涉及国际合作，促进与欧洲和加拿大同事的更紧密联系。国际地质年代界将受益于CA-TIMS的改进。UCSB的锆石实验室将得到分析预算的支持。

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.