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

该项目旨在研究锂在超大型火山爆发期间如何浓缩，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对锂的需求至关重要。该研究项目将研究麦克德米特火山口（内华达州/俄勒冈州），该火山口是美国最重要的锂矿床之一。通过研究火山岩中凝固的硅酸盐熔体的微观包裹体（“熔体包裹体”），Harlaux和Ruprecht博士将确定大约1600万年前在McDermitt发生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如何富含锂，并在岩浆放气过程中产生高温富锂蒸气，最终在火山口底部坍塌后形成锂矿床。里诺的内华达州大学的一名博士生将与来自STEM中代表性不足的人口群体的学生进行研究项目，特别鼓励他们申请。结果还将通过公共外展活动与更广泛的受众分享。该项目将直接有益于内华达州的经济和整个社会，因为它调查了美国西部其他火山口中锂的成矿潜力。该项目的核心是地壳中锂（Li）的地球化学循环，从而形成火山口中含锂粘土矿床。火山口形成系统中锂的富集被认为是由于岩浆分馏，然后脱气的富锂岩浆流体可能与大气降水的地下水混合，或再活化的锂在岩浆后沥滤火山玻璃的大气降水流体没有热液的贡献。考虑到大多数火山口不矿化与锂，问题出现了是否由大气降水单独的火山岩浸出是足够的，或富锂热液流体需要提供足够的锂为随后形成的intracaldera锂粘土矿床。本研究项目将集中在麦克德米特火山破火山口（内华达州/俄勒冈州），产生了大量的演变过碱性和过铝质岩浆和含锂粘土，形成后破火山口崩溃。通过研究来自不同中新世火山岩（约）的火成岩斑晶中的熔体和流体包裹体，Harlaux和Ruprecht博士将确定在McDermitt破火山口暴露的Li（16.7-16.0 Ma）如何在硅酸盐岩浆中逐渐富集，并在岩浆释气和岩浆系统冷却过程中分配到岩浆挥发相中。熔融包裹体和寄主石英斑晶的原位化学和同位素组成将分别通过EPMA和LA-ICP-MS分析主要和微量元素，以及西姆斯分析氧同位素。这项分析工作将允许调查锂富集在长寿命（约。该奖项反映了NSF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.