Collaborative Research: Development of 40Ar/39Ar Intercalibration Pipettes

合作研究：开发40Ar/39Ar相互校准移液器

• 批准号: 1057420
• 负责人: Alan Deino
• 金额: $ 5.4万
• 依托单位: Berkeley Geochronology Center
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-06-01 至 2014-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1057420&HistoricalAwards=false
• 关键词: Collaborative; Research; Development; 40Ar; 39Ar

Potassium (K), one of the more abundant elements in the Earth?s crust is found in many rock forming minerals. One of the isotopes of K, 40K is radioactive and decays to 40Ar. This scheme forms the physical basis for one of the most common geochronologic techniques applied to rocks and minerals. In recent years, a special technique requiring neutron bombardment of samples to produce 39Ar from 39K has become more favored than the traditional ?K-Ar? method, referred to as the 40Ar/39Ar method. In fact, the 40Ar/39Ar method of radioisotopic dating has the broadest range of applicability of any geochronometer, being useful from early solar system formation (~4.56 billion years ago) to volcanic materials as young as 2,000 years old. These studies cover topics such as volcanic and seismic hazards, timing and extent of mineralization events, global climate change and variability, paleomagnetic reversal timescale, and dating the fossil record, including human evolution. Thus any improvement in the accuracy and precision 40Ar/39Ar method will improve our understanding of the timing and rates of geologic processes.Despite exemplary precision, recent experiments conducted via the EARTHTIME initiative have revealed significant interlaboratory inconsistencies such that ages determined by different labs may vary by us much as 4 %, approximately an order of magnitude larger than typical reported measurement precision. Four possible causes for these discrepancies have been identified; 1) differences in the data reduction protocols employed by the participating laboratories; 2) unaccounted nonlinearity of the mass spectrometer source/detector systems used to collect the data; 3) unrecognized heterogeneity in the mineral standards or an experimental artifact arising from variations in neutron irradiation dosage in some of the sample packages; and 4) incomplete degassing or isotopic fractionation of Ar from the analyzed sanidines in various laboratories. This research project addresses the issue of interlaboratory consistency by developing an argon pipette system that will travel between the participating 40Ar/39Ar labs within the United States. The pipette system will deliver gas samples with exactly the same isotopic composition(s) and similar gas volume(s), thus controlling the variables and issues associated with heterogeneity of natural samples. In addition, variable gas sample volumes from the pipette system will also be measured to assess the response linearity of noble gas mass spectrometers. The ultimate goal of this study is to intercalibrate the various NSF supported 40Ar/39Ar laboratories and allow for the direct comparison of the ages produced from the participating labs, at the level of 0.1% or better. The long-term use of the pipette system will maintain the calibration between the 40Ar/39Ar laboratories. Undergraduate and graduate students will be traveling with the intercalibration pipette assisting with the measurements. This will provide the students the opportunity to see, work, and interact with personnel from the different 40Ar/39Ar laboratories and serve as a unique training opportunity for the next generation of geochronologist/isotope geochemists.

钾（k），是地壳中较丰富的元素之一，在许多形成矿物质的岩石中。 K，40K的同位素之一是放射性的，衰减至40AR。该方案构成了适用于岩石和矿物质的最常见的测量技术之一的物理基础。近年来，一项需要中子轰炸以从39K产生39AR的特殊技术比传统的？K-ar更受青睐？方法，称为40AR/39AR方法。实际上，40AR/39AR的放射性分析方法具有任何地球运动仪的最广泛适用性，这是从早期太阳系形成（约45.6亿年前）对2，000年历史的火山材料的有用。这些研究涵盖了诸如火山和地震危害，矿化事件的时机和程度，全球气候变化和可变性，古磁反转时间表以及对化石记录的约会，包括人类进化等主题。 因此，对准确性和精度40AR/39AR方法的任何提高都将提高我们对地质过程的时机和速率的理解。尽管如此，示例性的精确性，但最近通过Earth Time Initiative进行的最新实验已经显示出显着的跨代室间不一致，例如，不同实验室确定的AGES可以通过US 4％的级数，大约典型的级别均大于典型的阶段，而典型的级别可能会大于4％。已经确定了这些差异的四个可能原因； 1）参与实验室采用的数据减少协议的差异； 2）用于收集数据的质谱仪源/探测器系统的未划分的非线性； 3）在矿物标准标准中未识别的异质性或某些样品包装中中子辐照剂量的变化引起的实验性伪像； 4）来自各种实验室中分析的Sanidines的AR脱气或同位素分馏不完全。该研究项目通过开发一个将在美国境内的40AR/39AR实验室之间传播的氩移移系统来解决实验室中的一致性问题。移液器系统将提供具有完全相同的同位素组合物和相似气体体积的气体样品，从而控制与天然样品异质性相关的变量和问题。此外，还将测量来自移液器系统的可变气体样品体积，以评估贵重气体质谱仪的响应线性。这项研究的最终目的是对各种NSF支持的40AR/39AR实验室进行核对，并允许直接比较参与实验室产生的年龄，水平或更高的水平。长期使用移液器系统将保持40AR/39AR实验室之间的校准。本科生和研究生将以插入移液器的方式旅行，以协助测量。这将使学生有机会与来自不同40AR/39AR实验室的人员一起查看，工作和互动，并为下一代地球学学家/同位素地球化学家提供独特的培训机会。