Collaborative Research: Experimental Study of H, S, Cl, and F Partitioning Between Apatite, Fluid(s), and Melts: Applications to Magma Evolution and Volatile Component Exsolution

智力上的优点。挥发性组分水、碳、硫、氯、氟等影响岩浆流变和分异，控制火山脱气和喷发过程，影响岩浆组分在流体中的溶解和迁移，从而引起交代作用和热液成矿作用。火山岩浆挥发物的脱气也从根本上影响大气和海洋的地球化学，从而影响地球的气候。这些过程的效力直接随挥发物的丰度而变化。尽管通过分析火山岩和深成岩中的硅酸盐熔体包裹体和含水矿物对岩浆挥发性组分进行了广泛的研究，并进行了补充性的实验和理论研究，但目前对挥发性组分的行为和丰度的了解不足以准确模拟岩浆演化过程中的流体过程。特别是，我们必须更好地了解富含挥发分的岩浆流体何时首次出溶，它们的成分在岩浆演化过程中如何变化，以及这些流体如何积聚在岩浆房的顶部以控制岩浆过程和火山活动。普遍存在的矿物磷灰石[Ca5（PO4）3（OH，F，Cl）]含有氟、氯和氢氧根离子作为基本成分，也可能含有痕量至主要元素水平的硫。如果我们对元素分配有定量的了解，磷灰石就有可能被用来监测它所形成的岩浆中的挥发物含量。拟议的调查旨在提供必要的校准信息，通过受控实验和详细分析运行产品在已知的压力，温度和熔体组成。最终目标是开发磷灰石作为地球化学工具，用于：（1）估算熔体演化各阶段岩浆挥发分含量（并不总是以原生熔融包裹体的存在为代表），（2）追踪岩浆渐进演化过程中挥发性组分的行为，（3）阐明岩浆流体在脱气和火山喷发过程中的作用，（4）改进热力学模型，使之能够预测这些交换过程并应用于自然系统。更广泛的影响。这一项目可能会导致开发评估岩浆挥发分含量的强有力的替代方法。科学结果及其与社会的相关性将传达给参加美国自然历史博物馆的NSF支持的本科生研究经验（REU）计划的暑期实习生，并通过博物馆的讲座计划（专注于挥发物和地质过程）向教师和公众提供。博物馆还提供了许多其他机会，通过霍尔斯的电子媒体与公众分享科学研究成果。还将通过在马里兰州大学培训本科生和通过在马里兰州大学举办地球科学开放日活动教育公众来分享成果。

Intellectual merit. The volatile components water, carbon, sulfur, chlorine, and fluorine affect magma rheology and differentiation, control processes of volcanic degassing and eruption, and influence the dissolution and transport of magmatic components in fluids that cause metasomatism and hydrothermal mineralization. The degassing of magmatic volatiles from volcanoes also fundamentally affects the geochemistry of the atmosphere and oceans - thus influencing Earth's climate. The efficacy of these processes varies directly with the abundances of volatiles. Despite extensive study of magmatic volatile components via analyses of trapped silicate melt inclusions and hydrous minerals in volcanic and plutonic rocks, and complementary experimental and theoretical research, current knowledge of the behavior and abundances of volatiles is insufficient for accurate modeling of fluid processes during magma evolution. In particular, we must better understand when volatile-rich magmatic fluids first exsolve, how their compositions change during magma evolution, and how these fluids accumulate in the apices of magma chambers to control magmatic processes and volcanic activities. The ubiquitous mineral apatite [Ca5(PO4)3(OH,F,Cl)] contains fluorine, chlorine, and hydroxyl ions as essential constituents and may also contain trace- to major-element levels of sulfur. If we have quantitative knowledge of element partitioning, apatite potentially can be used to monitor volatile contents in the magmas from which it forms. The proposed investigation aims to provide that essential calibration information via controlled experiments and detailed analysis of run products formed at known pressure, temperature, and melt composition. The ultimate goal is to develop apatite as a geochemical tool for: (1) estimating magmatic volatile contents at various stages of melt evolution (not always represented by presence of primary melt inclusions), (2) tracking the behavior of volatile components during progressive magma evolution, (3) elucidating the role of magmatic fluids in processes of degassing and volcanic eruption, and (4) improving thermodynamic models that can predict these exchange processes and apply to natural systems. Broader Impacts. This project will likely result in development of powerful alternative methods for assessing magmatic volatile contents. The scientific results and their relevance to society will be conveyed to summer interns participating in an NSF-supported Research Experiences for Undergraduate students (REU) program at the American Museum of Natural History, and to teachers and the generall public via a lecture program (focused on volatiles and geologic processes) at the museum. The museum offers numerous other opportunities to share the results of scientific research with the public through electronic media in exhibition halls. The results will also be shared by training undergraduate students at the University of Maryland and by educating the public through an open-house event on Earth science at the University of Maryland.