Tracing lithium enrichment in the McDermitt caldera system by melt/fluid inclusions and in situ oxygen isotopes

该项目旨在研究锂如何在超大型火山爆发期间富集，最终形成锂矿床。锂是一种关键元素，对于支持电动汽车使用的可充电电池的快速发展和减轻气候变化的影响至关重要。因此，了解锂在地壳中的转移机制对于解决全球锂需求具有重要意义。该研究项目将研究麦克德米特火山火山口（内华达州/俄勒冈州），该火山口拥有美国最重要的锂矿床之一。通过研究火山岩中凝固硅酸盐熔体的微观包裹体（“熔体包裹体”）。哈劳克斯和鲁普雷希特将确定1600万年前在麦克德米特造成灾难性喷发的岩浆的化学成分。这项研究工作将有助于更好地了解岩浆是如何富集锂的，并在岩浆脱气过程中产生高温富锂蒸汽，最终在火山口底坍塌后形成锂矿床。内华达大学里诺分校（University of Nevada, Reno）的一名博士生将与来自STEM领域代表性不足群体的学生一起开展这项研究项目，这些学生被特别鼓励申请。还将通过与更广泛的受众进行公共宣传活动来分享成果。该项目将直接有利于内华达州的经济和整个社会，因为它可以调查美国西部其他火山口的锂矿化潜力。这个项目的核心是研究地壳中锂的地球化学循环，从而形成火山火山口中的含锂粘土矿床。在火山口形成系统中，锂的富集被认为是岩浆分馏后富锂岩浆流体脱气（可能与大气地下水混合）的结果，或者是在火山玻璃岩浆浸出后，大气流体在没有热液贡献的情况下对锂进行再活化的结果。考虑到大多数火山破火山口都没有被锂矿化，那么问题来了，仅仅是大气水对火山岩的浸出就足够了，还是需要富锂的热液来为随后形成的破火山口内的锂粘土矿床提供足够的锂。该研究项目将重点研究McDermitt火山破火山口（内华达州/俄勒冈州），该火山口产生了大量演化的过碱性和过铝质岩浆，以及在破火山口坍塌后形成的含锂粘土。通过研究麦克德米特火山口暴露的各种中新世火山岩（约16.7-16.0 Ma）中火成岩斑晶中的熔体和流体包裹体。Harlaux和Ruprecht将确定在岩浆脱气和岩浆系统冷却过程中，Li是如何在硅酸盐岩浆中逐渐富集并被划分到岩浆挥发阶段的。熔融包裹体和寄主石英斑晶的原位化学组成和同位素组成将分别用EPMA和LA-ICP-MS分析主元素和微量元素，并用SIMS分析氧同位素。这项分析工作将有助于研究麦克德米特岩浆系统长寿命（约1 Ma）期间的锂富集，以及在岩浆崩塌后立即脱气过程中，通过火山口底和火山口边缘释放的热液对锂的再活化。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 project aims to study how lithium concentrates during supergiant volcanic eruptions, eventually forming lithium ore deposits. Lithium is a critical element that is essential to support the rapid development of rechargeable batteries used by electric vehicles and to mitigate the impacts of climate change. Understanding the mechanisms of lithium transfer in the Earth’s crust is therefore of great importance to address the global demand for lithium. This research project will study the McDermitt volcanic caldera (Nevada/Oregon) which hosts one of the most important lithium deposits in the United States. By studying microscopic inclusions of solidified silicate melts trapped in volcanic rocks (“melt inclusions”), Drs. Harlaux and Ruprecht will determine the chemical composition of the magmas that generated a catastrophic eruption at McDermitt about 16 million years ago. This research work will help to better understand how magmas become enriched in lithium and can produce high-temperature lithium-rich vapors during magma outgassing, eventually forming lithium deposits after collapse of the caldera floor. A doctoral student at the University of Nevada, Reno, will conduct the research project with students from underrepresented demographic groups in STEM specifically encouraged to apply. Results will also be shared through public outreach activities with a broader audience. This project will benefit directly to Nevada’s economy and to society in general for investigating the mineralization potential for lithium in other volcanic calderas in the western United States.The geochemical cycle of lithium (Li) in the Earth’s crust yielding the formation of Li-bearing clay deposits hosted in volcanic calderas is at the center of this project. Enrichment of Li in caldera-forming systems is thought to result from either magma fractionation followed by degassing of Li-rich magmatic fluids possibly mixing with meteoric groundwaters, or remobilization of Li during post-magmatic leaching of volcanic glasses by meteoric fluids without hydrothermal contribution. Considering that most volcanic calderas are not mineralized with Li, the question arises whether leaching of volcanic rocks by meteoric water alone is sufficient, or Li-rich hydrothermal fluids are required to provide sufficient Li for the subsequent formation of intracaldera Li clay deposits. This research project will focus on the McDermitt volcanic caldera (Nevada/Oregon) that produced voluminous evolved peralkaline and peraluminous magmas and Li-bearing clays that formed after the caldera collapse. By studying melt and fluid inclusions hosted in igneous phenocrysts from diverse Miocene volcanic rocks (ca. 16.7-16.0 Ma) exposed in the McDermitt caldera, Drs. Harlaux and Ruprecht will determine how Li is progressively enriched in the silicate magmas and partitioned into the magmatic volatile phase during magma outgassing and cooling of the magmatic system. The in-situ chemical and isotopic composition of melt inclusions and the host quartz phenocrysts will be analyzed by EPMA and LA-ICP-MS for major and trace elements, respectively, and SIMS for oxygen isotopes. This analytical work will allow to investigate Li enrichment during the long-lived (ca. 1 Ma) lifetime of the McDermitt magmatic system and the remobilization of Li by hydrothermal fluids released through the caldera floor and along its margins during magma degassing immediately after collapse.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.