Constraining the release of oxidizing fluids from the mafic slab during subduction

俯冲过程中限制镁铁质板片中氧化流体的释放

• 批准号: 1946651
• 负责人: Ethan Baxter
• 金额: $ 24.87万
• 依托单位: Boston College
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-02-01 至 2023-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1946651&HistoricalAwards=false
• 关键词: Constraining; release; oxidizing; fluids; mafic

Subduction zones are key areas of geologic activity in which two plates collide and one plate is forced beneath the other and subducted deep into the Earth’s mantle. Subduction zones are responsible for some of the most important global geologic events and significantly impact humans and populated areas by causing earthquakes and creating large volcanic arcs such as the Pacific ‘Ring of Fire’. Uncertainty exists in the degree to which subduction zone volcanism is controlled by the exchange of material and fluids between the subducting plate and the overlying mantle rocks. One way to study such processes, is to analyze rocks that were previously subducted to great depths but have since been exhumed and returned to the Earth’s surface. The aim of this project is to investigate the record of the release and characteristics of fluids produced during subduction contained within individual garnet crystals in exhumed subduction zone rocks from the Western Alps (Italy/Switzerland). This study will further our understanding into the importance of subduction-derived fluids in controlling whether rocks within the subducting plate and the overlying mantle are more chemically oxidized or reduced, which will provide insights into their role in controlling volcanic arc magmatism. This project will support a post-doctoral researcher at Boston College, who will work with undergraduate students, providing them with training in analytical techniques and research experience. The research team from Boston College will work with a large network of collaborators from Europe and the US. An important component of this project will include undergraduate students travelling to Europe to conduct their own research with the help of European collaborators. Much debate exists around the role of metamorphic fluids, released during dehydration of the subducting slab, in controlling the redox conditions of the overlying sub-arc mantle and in explaining the oxidized and volatile-enriched geochemical signatures of volcanic arc magmas. The transfer of multi-valent, redox-sensitive elements such as S, C, and Fe from the subducting slab, represents a potential mechanism to produce oxidation of the sub-arc mantle. The proposed research will test the hypothesis that oxidizing species are released within fluids during dehydration of the mafic component of the slab during subduction. This study involves creating a field-based record of the release of fluids during subduction of the mafic crust, examining whether these fluids contain oxidizing species, and assessing the implications for changing redox conditions within the subducting mafic slab and overlying sub-arc mantle. To achieve this, the project will utilize the first coupled Fe and Zn isotopic analyses of growth zones within individual garnet crystals from exhumed high-pressure metamorphic rocks from the Western Alps. This will be combined with precise Sm/Nd zoned garnet geochronology to provide insights into the rates and timescales of redox-controlling metamorphic reactions. With the help of an international network of collaborators, this project aims to provide a uniquely high-resolution geochemical and geochronological dataset to assess processes occurring at the subduction zone interface and their relationship to oxidation of the sub-arc mantle and volcanic arc magmatism.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.

俯冲带是地质活动的关键领域，其中两个板碰撞和一块板在另一个板下面被迫俯冲到地球的深处。俯冲区负责某些最重要的全球地质事件，并通过造成地震并创造大型火山弧（例如太平洋“火环”）来重大影响人类和人口稠密的地区。不确定性在俯冲带火山的程度上通过俯冲板和上覆的地幔岩之间的材料和流体来控制的程度。研究此类过程的一种方法是分析以前俯冲到深度但此后被挖掘出来并返回地球表面的岩石。该项目的目的是研究来自西尔斯西部阿尔卑斯山（意大利/瑞士）中发掘的俯冲带岩石中各个石榴石晶体中包含的俯冲晶体中产生的流体的释放和特征的记录。这项研究将进一步理解俯冲衍生的流体在控制俯冲板中的岩石和上覆的地幔中是否更化学氧化或减少的重要性，这将提供有关它们在控制火山弧岩浆中的作用的见解。该项目将支持波士顿学院的博士后研究人员，他们将与本科生合作，为他们提供分析技术和研究经验的培训。波士顿学院的研究团队将与来自欧洲和美国的大型合作者网络合作。该项目的重要组成部分将包括在欧洲合作者的帮助下前往欧洲进行自己研究的本科生。在俯冲板脱水期间释放的变质流体的作用存在很多争论，在控制上覆的亚弧形地幔的氧化还原条件以及解释氧化和挥发性富含氧化的氧化和挥发性的地球学特征方面。从俯冲板中的多元氧化还原敏感元素（例如S，C和Fe）的转移代表了产生亚弧形壁炉氧化的潜在机制。拟议的研究将检验以下假设：在俯冲过程中，在木板成分的脱水过程中释放氧化物种。这项研究涉及创建基于田间的笛子释放的记录，以检查脱木皮地壳俯冲，检查这些笛子是否含有氧化物种，并评估对俯冲型具有脱落的脱氧物质板中改变氧化还原条件的意义，并覆盖了亚弧形的底漆。为了实现这一目标，该项目将利用来自西方阿尔卑斯山的发掘高压变质岩的单个石榴石晶体内的第一个耦合Fe和Zn同位素分析。这将与精确的SM/ND分区石榴石地质学结合使用，以洞悉氧化还原控制的变质反应的速率和时间标准。 With the help of an international network of collaborators, this project aims to provide a uniquely high-resolution geochemical and geochronological dataset to assess processes occurring at the subduction zone interface and their relationship to oxidation of the sub-arc mantle and volcanic arc magmatism.This award reflects NSF's statutory mission and has been deemed precious of support through evaluation using the Foundation's intellectual merit and broader impacts review 标准。