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

该奖项全部或部分由《2021年美国救援计划法案》（公法117-2）资助。“水晶时钟”技术利用保存在矿物中的元素浓度曲线来限制岩浆过程的时间尺度。岩浆补给、脱气、起泡、碎裂以及其他刺激物质运输和触发喷发的扰动，在岩浆最终上升前几小时到几秒钟就会发生。因此，只有扩散最快的阳离子，如挥发性元素锂（Li），才能保存这些快速火山事件的结晶记录。该项目的目标是通过实验量化长石固溶体中Li同位素的输运，以获得可应用于天然火山岩的数据，以确定这些岩浆事件的开始和持续时间。实验室实验将评估长石中总锂的扩散系数及其两种同位素的相对扩散系数，利用锂同位素地球化学的潜力来跟踪高温动力学过程。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，填补了对晶体时钟的需求，该晶体时钟适用于产生超级喷发的高度演化的大体积岩浆系统。除了提高对火山喷发时间尺度的理解所带来的知识价值外，该项目还具有更广泛的影响，包括制定Li质谱的社区标准和培训康奈尔大学的一名博士生。项目成果将纳入火山科学教育模块，与康奈尔监狱教育项目（CPEP）合作，将该模块交付给纽约州北部的在押人员。量化火山爆发的驱动因素是当今地球科学家面临的最重要的任务之一。长石中锂离子扩散计时器非常适合解决这一问题，因为长石固溶体存在于岩浆组成中，而长石中总锂的浓度可以通过激光烧蚀ICP-MS等常用分析工具很好地分辨出来。最近的研究发现，在多种晶体体系中，Li的扩散以复杂的机制发生，需要重新评估斜长石中现有的Li扩散系数，以准确量化岩浆过程的速率和时间尺度。该项目还将首次对钾长石中的Li扩散进行实验测量，并首次对长石中Li同位素的动力学分馏进行测量，这些数据对于区分由生长带产生的Li浓度曲线和由质量输运产生的Li浓度曲线至关重要。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

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.