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

科学依据：对地质时间的精确测量，尤其是精确的测量，仍然是破解岩石学、构造学和古生物学等广泛问题的最苛刻要求之一。锆石U-Pb年代学的“CA-TIMS”方法是一种新的高分辨率年代学方法（Mattinson, 2005），已经在精度和准确性方面取得了革命性的进步。我们现在需要更好地了解CA-TIMS的物理和化学性质，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，Pb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锆石中低温流体和辐射损伤介导的铅损失，及其对锆石年代学和合成锆石或类锆石材料中放射性废物的封存的影响。第三个主要目标是使用详细的、多步骤的CA-TIMS对精心挑选的一套天然锆石样品进行分析，以确定235U相对于238U的衰变常数。还将进行231Pa不平衡效应的初步研究，以及α -反冲过程对锆石中Pb重分布的意义。更广泛的影响：一至两名研究生和两至三名本科生将积极参与拟议研究的各个方面。这项研究的主要部分将涉及国际合作，与欧洲和加拿大的同事建立更密切的联系。国际地质年代学团体将受益于CA-TIMS的改进。UCSB锆石实验室将由分析预算支持。

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.