Collaborative Research: Incorporation of Metasedimentary Rocks into the Deep Levels of Continental Arcs: Insights from the North Cascades

合作研究：将变沉积岩纳入大陆弧深层：来自北部喀斯喀特的见解

• 批准号: 1419810
• 负责人: Stacia Gordon
• 金额: $ 20.55万
• 依托单位: Board of Regents, NSHE, obo University of Nevada, Reno
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-08-01 至 2019-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1419810&HistoricalAwards=false
• 关键词: Collaborative; Research; Incorporation; Metasedimentary; Rocks

The research contained in this project involves deciphering what chemical components are added into magmatic systems that form the roots of volcanoes at great depths during their evolution and incorporation into the Earth's crust. In some volcanic systems, magma derived from the Earth's mantle incorporates deeply buried sedimentary rocks, which has important implications for understanding the chemical composition of volcanic systems and the potential hazards associated with their eruption. The goal of this study is to evaluate how and when sediments rocks are transferred to deep levels beneath volcanic systems and how they affect the chemical evolution of the crust. The North Cascades of Washington represents an ancient magmatic system that has undergone collapse and significant erosion, which has allowed deep levels of the system to be exposed at the present-day Earth's surface. Using a variety of different radiogenic isotopic techniques, combined with field studies, the principal investigators will fingerprint the characteristics of source of the sedimentary rocks that were located in the deep levels of the ancient volcanic system. Possibilities for the origin of this material include sediments that were accumulated in front of a down going oceanic plate and then buried and melted as the plate was subducted. This information will provide crucial evidence for testing different structural and chemical models for the incorporation of sedimentary crust into magmas and will allow the PIs to fingerprint the material that feeds volcanic systems and possibly leads to large-scale volcanic eruptions, which has important societal impacts. Ultimately, this study is providing a more thorough understanding of the processes that control the nature and timescales of magmatism in modern and ancient continental volcanic arcs, which has implications for how new continental crust is formed. In addition to the scientific goals of this research, this project is supporting the training of graduate and undergraduate students in an STEM discipline, is supporting the research efforts of an early career scientist, and is contributing to research infrastructure at both collaborating institutions. Outreach efforts include the development of geologic brochures aimed at helping to educate visitors regarding the geologic evolution of North Cascades National Park and a website that summarizes research results. The principal investigators will also lead a field trip for professional geoscientists and students as part of an international meeting that will occur in Seattle in Fall 2017.Only a few field-based studies have examined how metasedimentary rocks become incorporated into the mid- to deep crust of continental magmatic arcs, even though their presence has significant mechanical and geochemical consequences for the arc system. Metamorphosed sedimentary rocks and their melts, produced if these rocks cross the solidus, are weak and thus strongly affect the overall rheology of the system. Emplacement of sediment into an arc via underplating may also control the timescales of magmatism and thus the architecture of the arc by driving the high-magma flux episodes noted in multiple ancient arc systems (e.g., Sierra Nevada, Coast Mountains-North Cascades). The principal investigators are evaluating how and when sediment is transferred into the mid to deep levels of arcs by investigating the importance of a range of processes, including 1) emplacement of subducted crustal material that rises buoyantly off of the downgoing slab (relamination); 2) burial by underthrusting/imbrication of forearc or backarc sediments; 3) gradual burial of sediments and volcanoclastic rocks during arc magmatism; and/or 4) construction of an arc on thickened crust that is already composed of voluminous metasedimentary rocks. The principal investigators will carry out an integrated field and laboratory study of the Late Cretaceous-Eocene crystalline core of the North Cascades. The principal investigators will determine the origin of the metasedimentary rocks via field mapping, bulk-rock Nd analyses, U-Pb and Hf-isotope study of detrital zircons, and thermobarometry to determine the tectonic context of these rocks, maximum-achieved pressures and source signatures. Analytical studies will also be conducted on detrital zircons from units in the forearc and backarc, which represent potential protoliths of the Skagit and Swakane metasedimentary rocks. The results from this study can be extrapolated to active arc systems (e.g., the Andes) to better understand the context of metasedimentary rocks: how they are emplaced within the arc system, and what the consequences are of their presence for the evolution of the arc and potentially for the overall production of andesitic continental crust. Another important outcome will be a better understanding of other ancient, potentially analogous arc systems, such as Fiordland, New Zealand and the Sierra Nevada.

该项目中包含的研究涉及破译将哪些化学成分添加到岩浆系统中，这些化学成分在进化过程中构成了极端的火山根，并将其掺入地球地壳中。 在某些火山系统中，岩浆源自地球的地幔，结合了深埋的沉积岩，这对了解火山系统的化学成分以及与其喷发相关的潜在危害具有重要意义。这项研究的目的是评估如何以及何时将沉积物岩石转移到火山系统下的深层水平，以及它们如何影响地壳的化学演化。华盛顿的北部级联代表着一种古老的岩浆系统，发生了崩溃和巨大的侵蚀，该系统使该系统的深层水平可以在当今的地球表面暴露。使用各种不同的放射同位素技术，结合现场研究，主要研究人员将指示位于古代火山系统深层的沉积岩来源的特征。 该材料起源的可能性包括沉积物，这些沉积物积聚在向下的海洋板块前，然后在俯冲时被掩埋和融化。 该信息将为测试不同的结构和化学模型提供至关重要的证据，以将沉积地壳掺入岩浆中，并使PIS可以指纹供应火山系统的材料，并可能导致大规模的火山喷发，这具有重要的社会影响。 最终，这项研究为控制现代和古代大陆火山弧的岩浆性的性质和时间尺度提供了更透彻的理解，这对新大陆壳的形成具有影响。除了这项研究的科学目标外，该项目还支持在STEM纪律中培训研究生和本科生的培训，支持早期职业科学家的研究工作，并为这两个合作机构的研究基础设施做出了贡献。推广工作包括开发地质手册，旨在帮助访客了解北喀斯喀特国家公园的地质演化以及总结研究结果的网站。作为国际会议的一部分，首席调查人员还将领导专业地球科学家和学生的实地考察，该国际会议将于2017年在西雅图举行。只有一些基于现场的研究研究了如何将沉积物岩石纳入大陆岩浆弧中的深层地壳中，即使它们的存在具有重大的机械和地球化学后果，对ARC系统具有重大的机械性和地球化学作用。如果这些岩石越过固体，则会产生变形的沉积岩及其熔体，从而较弱，从而强烈影响系统的整体流变学。通过低估，将沉积物扩散到弧中也可以控制岩浆的时间尺度，从而通过驱动多个古代弧系统中指出的高麦克马通量发作（例如，内华达州内华达州，海岸山脉山脉山cascades）中指出的高麦克马通量发作。主要研究人员正在评估如何以及何时通过研究一系列过程的重要性将沉积物转移到中部至深度弧中，其中包括1）将俯冲的地壳材料降低，从而使悬浮的板块浮出水面（复制）； 2）埋葬前臂或后弧形沉积物的埋葬/埋葬； 3）在弧岩岩岩中逐渐埋葬沉积物和火山碎屑岩石；和/或4）在厚厚的地壳上构造弧形，该弧形已经由大量的发质岩石组成。首席研究人员将对北级联的晚白垩世晶体核心进行综合田间和实验室研究。首席研究人员将通过田间映射，散装岩石分析，U-PB和HF - 同位素研究的碎屑锆石和热体计量法确定沉积物岩石的起源，以确定这些岩石的构造环境，最大程度的压力压力和源标志。分析研究还将对前臂和后弧的单位的碎屑锆石进行，这代表了Skagit和Swakane Saidimentary Rocks的潜在原石。这项研究的结果可以推断到主动弧系统（例如，安第斯山脉），以更好地理解沉积物岩石的背景：它们如何在ARC系统中放置，以及它们在ARC演变中的存在以及可能是对安德西斯大陆的整体生产的可能性。另一个重要的结果将更好地理解其他古老的，可能类似的弧形系统，例如Fiordland，New Zealand和Nevada。