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

该奖项的全部或部分资金来自《2021年美国救援计划法案》(公法117-2)。“水晶钟”技术使用保存在矿物中的元素浓度分布来限制岩浆作用的时间尺度。岩浆补充、脱气、起泡、碎裂和其他扰动，刺激物质传输并触发喷发，可能在最终岩浆上升前几个小时到几秒钟发生。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锂同位素在长石固溶体中的迁移，以产生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。将进行实验室实验，以评估总锂的扩散系数及其两个同位素在长石中的相对扩散系数，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，并产生第一个锂在钾长石中扩散的数据，以满足对适合应用于产生超级喷发的高度演化的大体积岩浆系统的晶体时钟的需求。除了更好地理解喷发时间尺度的学术价值外，该项目还产生了更广泛的影响，包括制定锂质谱分析的社区标准，以及在康奈尔大学培训一名博士生。项目成果将与康奈尔监狱教育计划(CPEP)合作，纳入火山科学教育模块，分发给纽约州北部的囚犯。量化火山喷发的驱动因素是当今地球科学家面临的最重要任务之一。锂在长石中的扩散计时仪是唯一适合于解决这一问题的仪器，因为在岩浆成分中发现了长石的固溶体，而且长石中的总锂浓度可以通过激光消融-电感耦合等离子体质谱等常用分析工具很好地解析。最近的工作发现，锂在各种晶体系统中以复杂的机制发生扩散，因此有必要重新评估斜长石中现有的锂扩散系数，以准确量化岩浆作用的速率和时间尺度。该项目还将首次实验测量锂在钾长石中的扩散，并首次测量锂同位素在长石中的动力学分馏，这些数据对于区分生长分区产生的锂浓度分布和大规模运输产生的锂浓度分布至关重要。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智力优势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.