SGER: Development of High-Precision Neodymium Isotope Mass Spectrometry to Search for Crust-Mantle Differentiation on Early Earth

SGER：开发高精度钕同位素质谱仪来寻找早期地球的壳幔分异

• 批准号: 0336405
• 负责人: Mukul Sharma
• 金额: $ 2.99万
• 依托单位: Dartmouth College
• 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: 2003-07-15 至 2005-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0336405&HistoricalAwards=false
• 关键词: SGER; Development; Precision; Neodymium; Isotope

EAR-0336405SharmaA major ambiguity remains in ascertaining whether the silicate portion of the Earth underwent differentiation during the first 500 million years of its history-a time for which there is no extant rock record. The evidence of early crust-mantle differentiation event(s) may be present in Archean rocks in the form of 142Nd anomalies produced from the decay of short-lived 146Sm (half-life = 103 million years), which was present at the time of formation of the Earth. The expected level of excess in 142Nd is about +30 parts per million (ppm) and, therefore, a 1-sigma uncertainty of 5 ppm or better is needed to resolve the anomaly. To accomplish this technically challenging task, we will use a new generation thermal ionization mass spectrometer (Triton) recently installed at Dartmouth.Initial measurements of standards on Triton have shown that it is capable of measuring anomalies in 142Nd exceeding +10 ppm. We will develop a standard operating procedure (SOP) to mitigate/eliminate possible ion optical artifacts in order to obtain Nd isotope results that are precise and accurate at 5 ppm (1-sigma) or better. Following the development of the SOP we will examine ten early Archean rocks from Isua, Greenland.Broader impacts of the proposed study include teaching and training of a highly motivated graduated student, Rasmus Andreasen, and development of new techniques of accurate and super-precise measurements of Nd isotopes using thermal ionization mass spectrometry. Also, the study is expected to provide new and profound insights into the history of early Earth differentiation. The unprecedented external reproducibility of Nd-isotope measurements will open up new avenues of investigations in diverse areas of earth and planetary sciences.

EAR-0336405Sharmaa的主要歧义仍然在确定地球的硅酸盐部分是否在其历史的前5亿年内进行了分化 - 没有现有岩石记录的时间。早期甲壳分化事件的证据可能存在于大帝岩石中，形式是从短暂的146SM（半寿命= 1.03亿年）中产生的第142个异常，该异常是在地球形成时出现的。 142nd中预期的过度水平约为百万分之30（ppm），因此需要1秒的不确定性为5 ppm或更高，以解决异常。为了完成这项技术具有挑战性的任务，我们将使用最近在达特茅斯（Dartmouth）安装的新一代热电离质谱仪（Triton）。特里顿（Triton）的标准测量结果表明，它能够在142nd中测量超过+10 ppm的异常。我们将开发一个标准的操作程序（SOP），以减轻/消除可能的离子光学伪像，以便获得ND同位素结果，这些结果在5 ppm（1-Sigma）或更高时精确而准确。随着SOP的发展，我们将检查格陵兰岛上的十个早期的Archean Rock。拟议的研究的影响包括使用热离子化质量图的ND同位体的精确且超级精确测量的新技术进行教学和培训。同样，这项研究有望为早期地球分化的历史提供新的深刻见解。 ND同位素测量的前所未有的外部可重复性将在地球和行星科学不同地区开辟新的调查途径。