In situ Rb-Sr mica petrochronology: a transformative approach to characterizing tectonic processes

原位铷-锶云母岩石年代学：表征构造过程的变革性方法

• 批准号: 2233868
• 负责人: Alicia Cruz-Uribe
• 金额: $ 39.13万
• 依托单位: University of Maine
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-01-15 至 2025-12-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2233868&HistoricalAwards=false
• 关键词: situ; Rb; Sr; mica; petrochronology

The radiogenic decay of 87Rb to 87Sr is an important “clock” that geologists use to measure the age of rocks and minerals. However, these measurements have traditionally required time-consuming lab work on pooled mineral separates. Several technical advances have recently alleviated this problem by enabling in-place (in situ) Rb-Sr measurements, but there are still barriers to their widespread use. These include a lack of appropriate reference materials, as well as questions about what Rb-Sr dates record in different rocks. This proposal addresses these problems in two ways. First, the researchers will develop two Rb-Sr reference glasses to significantly expand the use and application of Rb-Sr dating. They will also determine Rb-Sr dates from three well-studied rock suites, to provide key context for similar data elsewhere. This technique is novel because it allows us to accurately date mica, one of the most common minerals in Earth's crust. It also facilitates the measurement of rock Rb-Sr dates in less than an hour, far shorter than the traditional method (weeks to months). This project is led by middle and early career scientists and supports the professional development of two undergraduate and two graduate students. It additionally promotes scientific collaboration between two rural institutions in the northeastern US. The scientific goals of this proposal are two-fold. First, the researchers will produce two mica glasses (muscovite + biotite) and characterize them for major + trace elements and Rb-Sr isotopes. This includes high-precision isotope-dilution techniques as well as a community-wide, multi-instrument proficiency testing scheme (G-Probe). Their mica glass reference materials will be freely and widely disseminated, filling a critical analytical gap and spurring further development of the Rb-Sr technique in other labs, which will inevitably lead to other significant discoveries. As part of this effort, a data reduction scheme (DRS) for processing laser ablation Rb-Sr data will be further developed to include mass-shifted isotopes from multicollector instruments and downhole fractionation assessment. Second, they will determine in situ mica Rb-Sr dates by single- and multi-collector LA-ICP-MS/MS from three well-characterized locales representing endmember tectonic cases: the Mooselookmeguntic contact aureole, ME (USA); the Franciscan Subduction Complex, CA (USA); and the Ivrea-Verbano Zone, S. Alps (Italy). By performing campaign-style mica Rb-Sr geochronology in three tectonic case studies, within the context of other textural and geochemical data collected during this work, the researchers will test the behavior of the Rb-Sr system across a range of geologically relevant conditions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

87 Rb到87 Sr的放射性衰变是地质学家用来测量岩石和矿物年龄的重要“时钟”。然而，这些测量传统上需要对汇集的矿物分离物进行耗时的实验室工作。最近，一些技术进步通过实现就地（原位）Rb-Sr测量来缓解这一问题，但仍存在广泛使用的障碍。这些问题包括缺乏适当的参考材料，以及Rb-Sr年代在不同岩石中记录的问题。这项建议从两个方面解决这些问题。首先，研究人员将开发两种Rb-Sr参考玻璃，以显著扩大Rb-Sr测年的使用和应用。他们还将从三个经过充分研究的岩石套件中确定Rb-Sr日期，为其他地方的类似数据提供关键背景。这项技术是新颖的，因为它使我们能够准确地确定云母的年代，云母是地壳中最常见的矿物之一。它还有助于在不到一小时的时间内测量岩石Rb-Sr年龄，远远短于传统方法（数周至数月）。该项目是由中期和早期职业科学家领导，并支持两个本科生和两个研究生的专业发展。它还促进了美国东北部两个农村机构之间的科学合作。这项建议的科学目标是双重的。首先，研究人员将生产两种云母玻璃（白云母+黑云母），并对其进行主要+微量元素和Rb-Sr同位素的表征。这包括高精度同位素稀释技术以及社区范围的多仪器能力测试计划（G-Probe）。他们的云母玻璃参考材料将被免费广泛传播，填补了一个关键的分析空白，并刺激了其他实验室对Rb-Sr技术的进一步发展，这将不可避免地导致其他重大发现。作为这项工作的一部分，将进一步开发用于处理激光烧蚀Rb-Sr数据的数据简化方案（DRS），以包括来自多收集器仪器的质量偏移同位素和井下分馏评估。第二，他们将通过单和多收集器LA-ICP-MS/MS确定三个代表端元构造情况的特征良好的地点的云母Rb-Sr年龄：Mooselookmeguntic接触晕，ME（美国）; Franciscan俯冲复合体，CA（美国）;和Ivrea-Verbano带，S。阿尔卑斯山（意大利）。通过在三个构造案例研究中进行云母Rb-Sr地质年代学，在这项工作中收集的其他结构和地球化学数据的背景下，研究人员将测试Rb-Sr系统在一系列地质相关条件下的行为。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

项目成果

Single Spot Rb‐Sr Isochron Dating of Biotite by LA‐MC‐ICP‐MS / MS

LA-MC-ICP-MS / MS 对黑云母进行单点 Rb-Sr 等时线测年

• DOI: 10.1111/ggr.12518
• 发表时间: 2023
• 期刊: Geostandards and Geoanalytical Research
• 影响因子: 3.8
• 作者: Cruz‐Uribe, Alicia M.;Craig, Grant;Garber, Joshua M.;Paul, Bence;Arkula, Cemil;Bouman, Claudia
• 通讯作者: Bouman, Claudia