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、氯和氟影响岩浆的流变性和分异，控制火山脱气和喷发的过程，影响岩浆组分在流体中的溶解和迁移，导致交代和热液成矿。火山岩浆挥发物的脱气也从根本上影响了大气和海洋的地球化学--从而影响了地球的气候。这些过程的效果与挥发物的丰度直接相关。尽管通过分析火山岩和深成岩中捕获的硅酸盐熔体包裹体和水合矿物对岩浆挥发分进行了广泛的研究，并进行了补充的实验和理论研究，但目前对挥发分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第一次溶解的时间，它们的组成在岩浆演化过程中是如何变化的，以及这些流体是如何聚集在岩浆房的顶端以控制岩浆过程和火山活动的。无处不在的矿物磷灰石[Ca5(PO4)3(OH，F，Cl)]含有氟、氯和羟基离子作为基本成分，也可能含有微量到常量元素的硫。如果我们对元素分配有定量的了解，磷灰石可能会被用来监测形成磷灰石的岩浆中的挥发性含量。拟议的调查旨在通过受控实验和对在已知压力、温度和熔体组成情况下形成的运行产物的详细分析，提供必要的校准信息。最终目标是开发磷灰石作为一种地球化学工具，用于：(1)估计熔体演化不同阶段的岩浆挥发分含量(并不总是由原生熔体包裹体的存在表示)，(2)跟踪岩浆演化过程中挥发分的行为，(3)阐明岩浆流体在脱气和火山喷发过程中的作用，以及(4)改进热力学模型，以预测这些交换过程并应用于自然系统。该项目可能会导致开发出评估岩浆挥发分含量的强有力的替代方法。科学成果及其与社会的相关性将被传达给参加美国自然历史博物馆NSF支持的本科生研究体验(REU)项目的暑期实习生，以及通过博物馆的讲座项目(重点是挥发物和地质过程)传递给教师和普通公众。博物馆还提供了许多其他机会，通过电子媒体在展厅与公众分享科学研究成果。这些成果还将通过马里兰大学的本科生培训和通过马里兰大学的地球科学开放活动教育公众来分享。

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.