CAREER - Winding up our crystal clocks: Experimental studies of element diffusion in igneous minerals

火山及其下面的岩浆管道系统（岩浆库，管道）在时间尺度上运行，从几秒钟（一次爆炸性喷发）到数十万年（大型水库的逐步组装）不等。火山爆发前的不稳定，表现为不断增加的地震活动性或地面变形，往往与地下岩浆过程（岩浆上升，不同岩浆的混合，形成进入围岩的新通道）直接相关。因此，量化这些过程运行的时间尺度是火山学和基于情景的减灾的核心。对科学家来说幸运的是，岩浆携带矿物货物到地表，可以用作“水晶钟”。保存在矿物中的化学梯度代表矿物化学成分的不完全再均质化，可以通过一种称为扩散计时法的技术来估计梯度形成的持续时间。在岩浆温度下，化学元素在这些矿物中扩散/移动的速率需要首先通过实验室实验进行量化，以使该方法有效。然而，这些速率目前存在与简化实验设置相关的问题，并且可能无法直接适用于天然岩浆。该项目建议在高温下进行新的实验室实验，以更好地调整我们的水晶时钟，以帮助量化高威胁火山下的岩浆时间尺度。该项目还将“地球科学实验”作为一个共同的主题和教育目标。高中和大学本科生对STEM职业的兴趣在毕业前有所下降。由于数学、物理或化学的要求，STEM职业通常被认为很难，而成绩差距往往对代表性不足的少数族裔影响最大。夏威夷是美国最多样化的地方之一，但这种多样性尚未反映在地球科学本科招生中。通过一系列综合教育和推广活动，包括PI，夏威夷土著博士生，地球科学教育硕士学生，以及几名本科生和高级合作者，该项目旨在通过动手实验将高中生和本科生重新连接到科学和科学研究中。矿物中的扩散计时法是一种提取岩浆时间尺度的有力技术，它基于元素随时间扩散而产生的浓度梯度的程度。理论上，只要有合适的分析工具，并且元素扩散速率已知，该方法就可以用于解析任何时间尺度。在过去的二十年里，随着扩散系数的出现，扩散计时法在火成岩中的应用激增。这些系数是从涉及固体偶对的实验室实验中提取的，但天然岩浆矿物被熔体包围。熔固实验得出的少数扩散系数明显快于固固实验。该项目旨在更好地了解岩浆中矿物的扩散。(i)将在实验室使用橄榄石和斜长石进行一系列矿物-熔体扩散实验，以确定所获得的扩散系数是否与固体对相似或更高。分析工作和透射电镜成像将有助于理解所观察到的任何差异的机制。实验还将用于提取熔体-晶体分配系数。（二）将利用一项独特的、长达29年的自然实验（缓慢冷却的熔岩湖）来测试扩散计时技术。对1959-1988年收集的一系列岩心样品中的橄榄石进行分析，以研究橄榄石种群中元素的组成均匀性，并对已知温度历史样品进行详细的元素剖面，用于测试扩散计时法。这个项目的首要主题是实验，既用于研究也用于教育目的。在项目期间，将建立一个“规模地球实验室”，让学生参与科学推理过程，从设计到执行实验，收集和解释数据，以及与自然系统建立联系。本实验将为各层次的本科生提供经验，并在研究生的帮助下建立新的入门课程。实验室的移动部分将被带到高中，受益于现有的资助外展工作（EPIK）。我们将举办“科学星期六”活动，邀请高中生和他们的老师小团体参观实验和分析设施。重点将放在提供一个分层的指导结构，其中PI，毕业生，本科生都为学生提供建议。每个人都将接受培训，了解如何开展基于地点的调查，并认识到通过增加多样性和促进STEM研究的公平获取来加强我们的机构的必要性。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。

Volcanoes and their underlying magmatic plumbing systems (magma reservoirs, conduits) operate over timescales that vary between seconds (an explosive eruption) to several hundreds of thousands of years (progressive assembly of large reservoirs). Volcanic unrest prior to eruptions, expressed by increasing seismicity or ground deformation, tends to be directly correlated with subsurface magmatic processes (magma ascent, mixing of different magmas, formation of new pathways into the surrounding rock). Therefore, quantifying the timescales over which these processes operate is at the heart of volcanology and scenario-based hazards mitigation. Fortunately for scientists, magmas carry mineral cargo to the surface that can be used as ‘crystal clocks’. Chemical gradients preserved in minerals represent incomplete rehomogenization of the mineral’s chemical components, and can be used to estimate the duration over which the gradients formed through a technique called diffusion chronometry. The rate at which chemical elements diffuse/move in those minerals at magmatic temperatures needs to be first quantified through laboratory experiments for this method to be effective. However, these rates currently suffer from problems associated with simplified experimental setups and may not be directly applicable to natural magmas. This project proposes to carry out new sets of lab experiments at high temperature to better tune our crystal clocks, to aid in quantification of magmatic timescales under high threat volcanoes.The project also develops ‘Experiments in Geosciences’ as a common theme and educational goal. High school and college undergraduate student interest in STEM vocations has been shown to decline towards graduation. STEM careers are often deemed difficult due to math, physics or chemistry requirements, and achievement gaps tend to affect underrepresented minorities the hardest. Hawaii is one of the most diverse places in the US, yet this diversity is not yet reflected in undergraduate enrollment in Geosciences. Through series of integrated educational and outreach activities involving the PI, a Native Hawaiian PhD student, a MS student in Geoscience education, as well as several undergraduate students and senior collaborators, this project seeks to reconnect high school and undergraduate students to science and scientific research through hands-on experimentation. Diffusion chronometry in minerals is a powerful technique to extract magmatic timescales, based on the extent of concentration gradients produced by element diffusion with time. The method can theoretically be used to resolve any timescale, as long as suitable analytical tools are available, and the element diffusion rate is well known. Diffusion chronometry has experienced a surge in igneous applications over the last two decades as diffusion coefficients have become available. These coefficients are extracted from laboratory experiments involving solid couples, but natural magmatic minerals are surrounded by melt. The few diffusivities derived from melt-solid experiments appear significantly faster than their solid-solid counterparts. This project aims to better understand diffusion in minerals within magma. (i) Series of mineral-melt diffusion experiments will be carried out in the lab using olivine and plagioclase to determine whether diffusivities obtained are similar or higher than solid couples. Analytical work and TEM imaging will aid in understanding the mechanisms underpinning any differences observed. The experiments will also be used to extract melt-crystal partition coefficients. (ii) A unique, 29 year-long natural experiment (a slowly cooled lava lake) will be leveraged to test the diffusion chronometry technique. Olivine within a series of drill core samples collected 1959-1988 will be analyzed to study the compositional homogenization of elements within an olivine population, and detailed elemental profiles used to test the diffusion chronometry method with samples of known temperature histories. The overarching theme of this project is experimentation, both for research and educational purposes. A ‘scaled earth laboratory’ will be built during the project to allow students to engage in the science reasoning process, from designing to performing experiments, collecting and interpreting data, and making connections with natural systems. This lab will be exploited for undergraduate experiences at all levels and a new introductory course will be constructed with the help of the graduate students involved. Mobile portions of the lab will be taken to high schools, benefiting from an existing funded outreach effort (EPIK). We will conduct ‘Science Saturdays’ events, where small groups of high schoolers and their teachers are invited to tour the experimental and analytical facilities. Emphasis will be put on providing a tiered mentoring structure, where the PI, graduates, undergraduates all contribute to student advising. Everyone will get training on how to conduct Place-based investigations, and sensitized to the need to strengthen our institutions by increasing diversity and promoting equitable access to STEM research.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.