Synthesis of Lead-Doped Monazite Standards for Electron Microprobe Chemical Dating

用于电子探针化学测年的掺铅独居石标准品的合成

• 批准号: 0230019
• 负责人: Daniele Cherniak
• 金额: $ 5.18万
• 依托单位: Rensselaer Polytechnic Institute
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-01-01 至 2004-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0230019&HistoricalAwards=false
• 关键词: Synthesis; Lead; Doped; Monazite; Standards

Cherniak0230019Monazite is a tremendously versatile and durable recorder of rock events. It resists high-temperature diffusive equilibration, yet is reactive at low temperatures in the presence of hydrothermal fluids or significant deviatoric stress fields. Monazite responds to major phase reactions, and tags specific major or accessory phase reservoirs participating in the reaction through compositional zoning of elements such as Y, Th, U, Ca, Pb, and Si. It also records temperature information via (Y+HREE) distributions, and as monazite may be highly thorogenic, it can preserve the ages of some or all whole-rock events it experiences. However, natural monazites are compositionally quite complex, leading to inherent difficulty in both conventional analysis and electron microprobe (EMP) chemical age determination. Moreover, calibration for EMP chemical age determinations usually involves a secondary standardization to monazite with a measured isotopic age. This is problematic because chemical age may be distinct from one or more isotopic ages, and calibration should be set to a concentration, not an age, as elemental concentrations are measured during analysis. We propose the following work: 1) Pb-doped REE phosphate will be synthesized and fully characterized via EMP and XRD as a chemical age standard. We demonstrate that minor amounts (to wt. % level) of lead are stable in monazite, and incorporation of known amounts of lead, along with Th- and U-monazite components, will allow calibration to a standard of known composition rather than inferred age; 2) Pb-doped unary REE phosphates will be synthesized to aid EMP age analysis protocols, by isolating lead with a single rare earth element so as to examine Pb interferences as a function of detector gas plus detector and collimator settings; 3) Isotopic monazite standards will be synthesized by doping (REE, Th, U, Ca) phosphate with Pb of known isotopic composition. Standards will be freely distributed to interested analysts, fostering mutual collaboration and sharing of methods and results.

Cherniak0230019monazite是岩石事件的通用和耐用录音机。它抵抗了高温扩散平衡，但在存在水热流体或明显的偏斜应力场的情况下，在低温下具有反应性。独居石对主要相反应的反应，并通过Y，Th，Th，U，Ca，Pb和Si等元素的组成分区来标记参与反应的特定主要或附属相。它还通过（y+hree）分布记录温度信息，并且由于独居石可能具有高度胸腔，因此可以保留其经历的某些或所有全摇滚事件的年龄。然而，天然的独占在构图上非常复杂，导致常规分析和电子微探针（EMP）化学年龄确定的固有难度。此外，针对EMP化学年龄确定的校准通常涉及以测得的同位素年龄的二级标准化。这是有问题的，因为化学年龄可能与一个或多个同位素年龄不同，并且应将校准设置为浓度而不是年龄，因为在分析过程中测量了元素浓度​​。我们提出以下工作：1）通过EMP和XRD作为化学年龄标准，将合成并完全表征PB掺杂的REE磷酸REE磷酸盐。我们证明，铅的较小含量（至wt。％）在独居石中是稳定的，并且掺入已知量的铅，以及Th-和U-Monazite组件，将允许校准已知成分的标准，而不是推断的年龄。 2）通过用单个稀土元素隔离铅，以检查Pb干扰的铅作为检测器气体加上检测器和直接仪的设置，将合成PB掺杂的一元REE磷酸盐，以帮助EMP年龄分析方案。 3）同位素独居石标准标准将通过掺杂（REE，th，u，ca）磷酸盐和已知同位素组成的Pb合成。标准将自由分发给感兴趣的分析师，促进相互协作并共享方法和结果。