Calibration of the Lithium-in-Feldspar Geospeedometer for Timing Magmatic Events

用于岩浆事件计时的锂长石地球速度计校准

• 批准号: 2100527
• 负责人: Megan Holycross
• 金额: $ 40.59万
• 依托单位: Cornell University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-08-15 至 2025-07-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2100527&HistoricalAwards=false
• 关键词: Calibration; Lithium; Feldspar; Geospeedometer; Timing

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). “Crystal clock” techniques use element concentration profiles preserved in minerals to constrain the timescales of magmatic processes. Magma recharge, degassing, foaming, fragmentation, and other perturbations that spur mass transport and trigger eruptions can occur mere hours to seconds before final magma ascent. Thus, only the fastest-diffusing cations, like the volatile element lithium (Li) will preserve a crystalline record of these rapid volcanic events. The goal of this project is to experimentally quantify the transport of Li isotopes in feldspar solid solutions to yield data that can be applied to natural volcanic rocks to determine the onset and duration of these magmatic events. Laboratory experiments will be run to assess the diffusivities of both total Li and the relative diffusivities of its two isotopes in feldspar, harnessing the potential of Li isotope geochemistry to track high-temperature kinetic processes. This project will also re-assess existing Li diffusion data in plagioclase feldspars and produce the first data for Li diffusion in potassium feldspars, filling a need for crystal clocks that are suitable for application to the highly evolved, large volume magma systems that produce super eruptions. In addition to the intellectual merits of improved understanding of eruption timescales, this project has broader impacts that include development of community standards for Li mass spectrometry and training of a PhD student at Cornell University. Project outcomes will be incorporated into an educational module on volcano science that will be delivered to incarcerated persons in upstate New York in collaboration with the Cornell Prison Education Program (CPEP).Quantifying the drivers of volcanic eruptions is one of the most important tasks facing Earth scientists today. A Li-in-feldspar diffusion chronometer is uniquely suited to address this task because feldspar solid solutions are found across magma compositions and concentrations of total Li in feldspar are well-resolved by common analytical tools like laser ablation ICP-MS. Recent work has found that Li diffusion occurs by complex mechanisms in a variety of crystal systems, necessitating a re-assessment of existing Li diffusion coefficients in plagioclase feldspars to accurately quantify the rates and timescales of magmatic processes. This project will also produce the first experimental measurements of Li diffusion in potassium feldspars and the first measurements of the kinetic fractionation of Li isotopes in feldspar, data which are critical for discriminating between Li concentration profiles produced by growth zoning and those produced by mass transport.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.

该奖项的全部或部分资金来源于《2021 年美国救援计划法案》（公法 117-2）。“水晶钟”技术利用矿物中保存的元素浓度分布来限制岩浆补给、脱气、泡沫、碎裂和其他刺激物质输送并引发喷发的扰动可能会在最终岩浆上升之前的几小时到几秒内发生，因此，只有扩散最快的阳离子，如阳离子。挥发性元素锂（Li）将保存这些快速火山事件的晶体记录，该项目的目标是通过实验量化长石固溶体中锂同位素的传输，以获得可应用于天然火山岩以确定火山爆发的数据。这些岩浆事件的持续时间将进行实验室实验，以评估长石中总锂的扩散率及其两种同位素的相对扩散率，以利用锂的潜力。该项目还将重新评估斜长石中现有的锂扩散数据，并产生钾长石中锂扩散的第一个数据，满足对适用于高温动力学过程的晶体钟的需求。除了提高对喷发时间尺度的理解的智力价值外，该项目还具有更广泛的影响，包括制定锂社区标准。康奈尔大学博士生的质谱分析和培训项目成果将纳入火山科学教育模块，该模块将与康奈尔监狱教育计划 (CPEP) 合作向纽约州北部的被监禁者提供。火山喷发的研究是当今地球科学家面临的最重要的任务之一，长石锂扩散计时器特别适合解决这项任务，因为在岩浆成分和总浓度中都发现了长石固溶体。激光烧蚀 ICP-MS 等常用分析工具可以很好地解析长石中的锂，最近的工作发现，锂在各种晶体系统中的扩散是通过复杂的机制发生的，因此需要重新评估斜长石中现有的锂扩散系数，以确保锂在长石中的扩散。该项目还将首次对钾长石中的锂扩散进行实验测量，并首次对锂的动力学分馏进行测量。长石中的同位素，这些数据对于区分生长分区产生的锂浓度分布和大众运输产生的锂浓度分布至关重要。该奖项是 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。