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，或海洋构造板块被拉入地球深处的区域，是我们星球上最具活力的地方之一。重要的是，它们促进了岩浆从地球内部地幔层转移到地球表面。这种岩浆活动最清楚地表现为火山爆发，几条证据表明，这一过程是大陆地壳在整个地球历史上的形成过程。然而，岩浆转移的速率并不是恒定的。在俯冲带内有被称为岩浆“爆发”的强烈岩浆活动时期。这些间断事件代表了大量物质和热能转移到地壳中，描绘其原因和后果对于理解这些动态构造环境的长期演变非常重要。这项研究的重点是岩浆爆发和地壳变形之间的关系，通过比较两个时期的强烈岩浆活动在北喀斯喀特山脉，华盛顿，发生在78-60和50-45百万年前。这一地区是研究的理想之地，因为随后的构造事件，加上侵蚀，在两次爆发事件期间，代表各种地壳深度的岩石并置在一起，并使这些岩石暴露在地球表面。研究人员将利用这个天然实验室创建一个详细的岩浆输入时间轴，与地壳增厚和随后变薄、断层和韧性、软弱地壳流动的区域证据进行比较。作为该项目的一部分，研究人员将制作一个科学播客，将这项研究的结果传达给公众。该播客将突出女性地球科学家在该项目中的作用，目标是增加STEM相关职业中女性的招聘和保留。 拟议的研究将记录在岩浆爆发事件期间和之间大陆弧地壳的流变演化。研究人员建议利用华盛顿北喀斯喀特山脉的一个暴露良好且研究相对充分的地壳剖面，该剖面保存了白垩纪末和古近纪末两次爆发事件期间和之间的岩浆作用、变质作用和地壳深部变形的记录。俯冲和纳入沉积物到深层次的弧发生在部分的老耀斑，和年轻的耀斑的结束阶段是同时代的深弧地壳的折返。研究人员将利用尖端的地球化学，地质年代学，热压和现场技术对弧内的火成岩侵入体和变质沉积岩进行组合，包括那些暴露在主要断层系统内的岩石。这项研究的一个关键组成部分是使用铀-铅锆石地质/热年代学创建两次耀斑事件期间岩浆添加的高时间分辨率记录，可以直接与由铀-铅锆石、独居石和钛铁矿地质/热年代学组合确定的变质、韧性变形和断层的类似记录进行比较，石榴石地质压力计中新石英的应用，以及传统的野外和微观结构研究。这种方法将提供一个全面的了解岩浆爆发，以及它们如何影响俯冲带地壳的流变学在100万年的规模。特别是，主要调查人员将探讨：弱化的深层地壳与爆发岩浆活动之间的时间关系;弧形边界断层系统何时相对于爆发变得活跃;变形如何在不同的岩性和结构之间分配;在爆发期间是否以及何时发生地壳熔化;以及在爆发期间和爆发之间地壳厚度是否保持不变。更广泛的影响将包括培训研究生，并通过开发和宣传与拟议研究区的路边地质有关的播客系列，为公众宣传创建一个长期的计划，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查进行评估，被认为值得支持的搜索.