Collaborative Research: Investigating the Relationships Between Magmatic 'Flare-Ups', Crustal Rheology, and Arc Collapse

合作研究：调查岩浆“爆发”、地壳流变学和弧塌陷之间的关系

• 批准号: 1945260
• 负责人: Michael Eddy
• 金额: $ 34.98万
• 依托单位: Purdue University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-07-15 至 2024-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1945260&HistoricalAwards=false
• 关键词: Collaborative; Research; Investigating; Relationships; Between

Subduction zones, or areas where oceanic tectonic plates are pulled into the deep Earth, are one of the most dynamic locations on our planet. Importantly, they facilitate the transfer of magma from the Earth’s interior mantle layer to its surface. This magmatism is most clearly expressed as volcanic eruptions, and several lines of evidence suggest that this process is how continental crust has been made throughout Earth’s history. Nevertheless, the rate of magma transfer is not constant. There are well-documented periods of intense magmatism within subduction zones that are known as magmatic ‘flare-ups’. These punctuated events represent a large transfer of material and thermal energy into the Earth’s crust, and delineating their causes and consequences is important for understanding the long-term evolution of these dynamic tectonic settings. This study is focused on the relationship between magmatic flare-ups and deformation of the crust by comparing two periods of intense magmatism within the North Cascade Range, Washington, that occurred 78–60 and 50–45 million years ago. This area is ideal for the study because subsequent tectonic events, combined with erosion, have juxtaposed rocks that represent a variety of crustal depths during both flare-up events and have exposed these rocks at the Earth’s surface. The researchers will use this natural laboratory to create a detailed timeline of magmatic input compared to regional evidence for thickening and subsequent thinning of the Earth’s crust, faulting, and flow of ductile, weak crust. As part of this project the researchers will produce a scientific podcast that will communicate the results of this study to the general public. The podcast will highlight the role of women geoscientists in the project, with the goal of increasing recruitment to and retention of women in STEM-related careers. The proposed research will document the rheological evolution of continental arc crust during and between magmatic flare-up events. The researchers propose to exploit a well-exposed and relatively well-studied crustal section in the North Cascades, Washington, which preserves a record of magmatism, metamorphism, and deformation in the deep to upper crust during and between two flare-up events in the latest Cretaceous and Paleogene. Underthrusting and incorporation of sediment into the deep levels of the arc occurred during part of the older flare-up, and the end stage of the younger flare-up is coeval with exhumation of the deep arc crust. The researchers will utilize cutting-edge geochemical, geochronologic, thermobarometric, and field techniques on a combination of igneous intrusions and metasedimentary rocks within the arc, including those exposed within major fault systems. A key component of this study will be to create a high temporal resolution record of magma addition during the two flare-up events using uranium-lead zircon geo-/thermochronology that can be directly compared to a similar record of metamorphism, ductile deformation, and faulting determined by a combination of uranium-lead zircon, monazite, and titanite geo-/thermochronology, application of the new quartz in garnet geobarometer, and traditional field and microstructural study. This approach will provide a holistic understanding of magmatic flare-ups and how they affect the rheology of subduction zone crust on a 1-million-year-scale. In particular, the principal investigators will address: the temporal relationship between a weakened deep crust and flare-up magmatism; when the arc-bounding fault systems became active relative to flare-ups; how deformation was partitioned across different lithologies and structures; if and when crustal melting occurred during a flare-up; and if crustal thickness stayed constant during and between flare-ups. The broader impacts will include training of graduate students and creating a long-lasting program for public outreach through the development and advertisement of a podcast series tied to the roadside geology of the proposed research area, which is in the Ross Lake National Recreation Area.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.

俯冲带或将海洋构造板拉入深层地球的区域，是我们地球上最动态的位置之一。重要的是，它们促进了岩浆从地球内部地幔层转移到其表面。这种岩浆作用最清楚地表达为火山喷发，有几条证据表明，这一过程是在整个地球历史上如何制作大陆壳的方式。然而，岩浆转移的速率不是恒定的。俯冲带中有充分记录的岩浆岩岩段时期，被称为岩浆“爆炸”。这些标点的事件代表了将材料和热能转移到地壳中的大量转移，并描绘出它们的原因和后果对于理解这些动态构造环境的长期演变很重要。这项研究的重点是通过比较华盛顿北部喀斯喀特山脉内的两个激烈的岩浆作用，这是78-60和50-45亿年前发生的两个时期的岩浆爆发与地壳变形之间的关系。该区域是研究的理想选择，因为随后的构造事件与侵蚀结合在一起，并置了岩石，它们在两个爆炸事件中代表了各种地壳深度，并将这些岩石暴露在地球表面。与区域性证据相比，研究人员将使用该天然实验室来创建一个详细的岩浆输入时间表，以证明地球的外壳，断层和延展性，弱地壳的变化和随后变薄。作为该项目的一部分，研究人员将制作一个科学的播客，将本研究的结果传达给公众。播客将强调女性地球科学家在该项目中的作用，目的是增加妇女在与STEM相关的职业中的招聘和保留。拟议的研究将记录在岩浆爆炸事件期间和之间连续弧形地壳的流变学演变。研究人员建议在华盛顿北部级联探索一个曝光且相对良好的地壳部分，该区域保留了岩浆，变质和变形的记录，并在最新白垩纪和古近纪期间的两个爆发事件中和两次爆发事件中的深层地壳中保留了记录。在较老的爆发的一部分中发生了沉积物与深层层次的凹陷和融合的关联，而年轻的爆发的末端阶段则是散发的，并散发出深弧壳的发掘。研究人员将利用尖端的地球化学，地质学，热量和野外技术，结合了火成岩侵入和弧内的发电岩石，包括在主要断层系统中暴露的岩石。这项研究的一个关键组成部分是在两次爆发事件期间使用铀潜在锆石的地理学/热量体创建高临时分辨率记录，可以将其与类似的变质，延性变形的记录直接进行比较，并由铀，荷兰氮杂型，单位虫（Monazite gorrony）的组合确定，并确定了脉络含量的组合。地理位计以及传统领域和微观结构研究。这种方法将对岩浆爆发以及它们如何影响100万年级的俯冲带壳的流变学提供整体理解。特别是，首席研究人员将解决：弱化的深皮和爆炸岩浆症之间的临时关系；当弧形断层系统相对于爆发而变得活跃时；如何在不同的岩性和结构之间分配变形；如果以及爆炸期间发生地壳融化的时候；如果地壳厚度在爆炸中和之间保持恒定。更广泛的影响将包括对研究生的培训，并通过开发和广告与拟议的研究领域的路边地质相关的播客系列的开发和广告创建持久的计划，该系列在罗斯湖国家娱乐区（Ross Lake National Recreation Areation）。该奖项反映了NSF的法定任务，反映了通过使用基金会的智力效果和广泛的评估来进行评估，并以评估为贵族。