Postdoctoral Fellowship: EAR-PF: Investigating spatiotemporal variability of forearc mantle wedge serpentinization and rheology during non-steady state subduction

盖布·爱泼斯坦博士获得了美国国家科学基金会地球科学博士后奖学金，在迈阿密大学亚当·霍尔特博士的指导下，他开展了旨在限制弧前地幔楔形水化的原因、可变性和后果的研究。在两个构造板块交汇的地区，俯冲是“俯冲”板块向“俯冲”板块下方挤压，然后下降到地幔深处的过程；这一过程发生在世界各地约50,000公里的海岸线上，包括华盛顿州和阿拉斯加州、日本岛和南美洲西海岸。当水从俯冲板块释放到俯冲板块(弧前地幔楔体)上方的地幔部分时，地幔楔形水化就会发生，只有当地幔的弧前区域足够冷，才能使含水矿物保持稳定时，才能进行地幔楔形水化。从俯冲板块释放的水和相关的楔形水化作用可能有助于弧形火山(例如，环太平洋的“火环”)的定位和强度以及大震级地震。尽管地幔楔形水化的这种潜在重要性，这种水化作用的时间变异性和后果没有得到很好的解决，通常是因为在针对这些过程的研究中，俯冲系统的动态和依赖于时间的性质通常被忽视。该项目将把新的计算方法与实验室分析相结合，以调查前弧中的流体释放和楔形水化作用如何有助于俯冲动力学(例如，俯冲带的速度和形状)，以及这种动力学对火山活动、地震活动、地幔中的水储存和地球的长期宜居性的影响。利用这些研究成果，爱泼斯坦博士将开发一系列可访问的、开源的在线学习模块，旨在扩大对与社会、福利和公平有关的地球科学问题的理解。这些模块的设计将允许参与者(公共和高中生到本科生)与大型数据集互动并操纵软件代码。总的来说，学习成果将是展示地球科学与其他研究分支(自然科学和社会科学、工程学、艺术)之间的联系，并突出现代地球科学家的无数研究努力(实验室、计算和实地)。研究和更广泛的影响目标将在跨学科科学中产生新的途径，并将通过加强科学界和普通公众对自然灾害和全球长期水循环的了解，为促进国家福利的NSF目标做出贡献。爱泼斯坦将把开源软件(Python、Perple_X和Aspect)与挖掘出的岩石记录中的化学/流变学见解结合起来，在一系列俯冲条件下开发流体释放和伴随的弧前地幔楔形水化的动力学模型，以更好地约束地幔水化的程度、时空变异性和化学/地球动力学后果。该项目的目标是：(1)通过地球动力学模拟，确定俯冲带生命周期中楔形水化作用的相对时间和程度，以及相关的矿物学和粘度的时空变异性；(2)对天然楔形蛇纹岩进行显微结构观察，以表征各种P-T条件下的变形机制；以及(3)利用微量元素比率和稳定同位素分析来确定流体流动和变形机制之间的关系。这些目标是迭代的，来自(2)和(3)的见解反馈到地球动力学模型(1)。将对来自New Idria(美国加利福尼亚州；蓝片岩相)、墓地山脊(美国亚利桑那州；角闪岩相)和西部阿尔卑斯山(意大利/法国；绿片岩至榴辉岩)的代表地幔楔形蛇纹岩或类似物的样品进行实验室化学(主要和微量元素、稳定N同位素分析)和晶体/流变学数据(变形机制的现场表征、EBSD和拉曼光谱)。俯冲带热演化的最早阶段(S)负责稳定地幔楔体中的大量含水物质，这种物质的流变行为取决于水化的程度和分布，以及粘性变形的温度和速率。这项研究的传播将包括开发一系列方便、有经验的在线学习模块，作为Jupyter笔记本(通过Binder)托管，面向高中生和本科生，目的是展示地球科学、化学、物理和编码之间的相互作用。通用的学习设计(UDL)教育框架将在整个模块的创建过程中创造一个可访问的和公平的学习环境。该EAR-PF奖由EAR构造计划共同资助。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Dr. Gabe Epstein has been awarded an NSF Earth Sciences Postdoctoral Fellowship to carry out research aimed at constraining the causes, variability, and consequences of forearc mantle wedge hydration under the mentorship of Dr. Adam Holt at the University of Miami. At regions where two tectonic plates converge, subduction is the process by which the “subducting” plate thrusts beneath the “overriding” plate and then descends to great depths within the mantle of the Earth; this process occurs along ~50,000 km of coastline around the world including beneath the states of Washington and Alaska, the Island of Japan, and the west coast of South America. Mantle wedge hydration occurs when water is released from the subducting plate into the section of the Earth’s mantle that lies above the subducting plate (the forearc mantle wedge) and can only proceed if this forearc region of the mantle is cool enough for water-bearing minerals to be stable. Release of water from the subducting plate, and the associated wedge hydration, may contribute to the localization and intensity of arc volcanoes (e.g., the “ring of fire” surrounding the Pacific Ocean) and large magnitude earthquakes. Despite this potential importance of mantle wedge hydration, the temporal variability and consequences of this hydration are poorly resolved, often because the dynamic and time-dependent nature of subduction systems is typically neglected in studies that target these processes. This project will merge novel computational methods with laboratory analysis to investigate how fluid release and wedge hydration in forearcs contributes to subduction dynamics (e.g., the speed and shape of subduction zones), and the impacts such dynamics have on volcanism, seismicity, water storage in the mantle, and Earth’s long-term habitability. Utilizing the research findings, Dr. Epstein will develop a series of accessible, open-source, online learning modules aimed at broadening understanding of geoscience problems pertinent to society, welfare, and equity. The design of the modules will allow for participants (the public and high school to undergraduate students) to interact with large datasets and manipulate software code. Broadly, the learning outcomes will be to demonstrate connectivity between geoscience and other branches of research (natural and social sciences, engineering, art), and to highlight the myriad research endeavors of modern geoscientists (laboratory, computational, and field based). The research and broader impact goals will produce new avenues in interdisciplinary science and will contribute to the NSF goal of advancement of national welfare by enhancing both the scientific community’s and the general public’s understanding of natural disasters and the global, long-term water cycle.Dr. Epstein will merge open-sourced software (Python, Perple_X, and ASPECT) with chemical/rheological insights from the exhumed rock record to develop dynamic models of fluid release and concomitant forearc mantle wedge hydration over a range of subduction conditions to better constrain the extents, spatiotemporal variability, and chemical/geodynamic consequences of mantle hydration. The project goals are: (1) determine the relative timing and extents of wedge hydration during a subduction zone’s lifetime, and the associated spatio-temporal variability in mineralogy and viscosity, through geodynamic modeling; (2) perform microstructural observations of natural wedge serpentinites to characterize deformation mechanisms over a range of P-T conditions; and (3) use trace element ratios and stable isotope analysis to determine the relationship between fluid flow and deformation mechanism. These goals are iterative, with insights from (2) and (3) feeding back into the geodynamic model (1). Laboratory chemical (major and trace element, stable N isotope analysis) and crystallographic/rheologic data (in-situ characterization of deformation mechanisms, EBSD, and Raman spectroscopy) will be performed on samples representing mantle wedge serpentinites or close analogs from New Idria (California, USA; blueschist facies), Cemetery Ridge (Arizona, USA; amphibolite facies), and the Western Alps (Italy/France; greenschist through eclogite). It is expected that earliest phase(s) of the thermal evolution of subduction zones is responsible for stabilization of large volumes of hydrous material in the mantle wedge, and that the rheologic behavior of this material varies depending on the extents and distribution of hydration combined with the temperatures and rates of viscous deformation. Dissemination of the research will include development of a series of accessible, experiential, online learning modules hosted as Jupyter Notebooks (via Binder) and geared towards high school and undergraduate students with the aim of demonstrating the interplay among geoscience, chemistry, physics, and coding. The Universal Design for Learning (UDL) educational framework will be utilized to create an accessible and equitable learning environment throughout creation of the modules.This EAR-PF award was co-funded by the EAR Tectonics Program.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.