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: 1945352
• 负责人: Robert Miller
• 金额: $ 7.78万
• 依托单位: San Jose State University Foundation
• 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 2025-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1945352&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，是地球上最具活力的位置之一。重要的是，它们促进了岩浆从地球内部地幔层到地表的转移。这种岩浆作用最清楚地表现为火山喷发，几行证据表明，这一过程就是整个地球历史上大陆地壳的形成过程。然而，岩浆转移的速度并不是恒定的。在俯冲带内有一段有充分证据的强烈岩浆活动时期，这种时期被称为岩浆“爆发”。这些断断续续的事件代表着物质和热能大量转移到地壳中，描绘它们的原因和后果对于理解这些动态构造环境的长期演化非常重要。通过对比78-60年和5,000万-4,500万年前华盛顿北级联山脉内的两个强烈岩浆活动时期，重点研究了岩浆爆发与地壳形变的关系。这一地区是研究的理想区域，因为随后的构造事件与侵蚀相结合，在两次爆发事件中将代表不同地壳深度的岩石并列在一起，并将这些岩石暴露在地球表面。研究人员将利用这个自然实验室来创建一个详细的岩浆输入时间线，与地壳增厚和随后减薄、断层以及韧性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，向公众传达这项研究的结果。播客将突出女性地球科学家在该项目中的作用，目标是增加妇女在STEM相关职业中的招聘和留住。拟议的研究将记录大陆弧壳在岩浆爆发事件期间和之间的流变演化。研究人员提议开发华盛顿州北喀斯喀兹地区一个暴露良好、研究相对充分的地壳剖面，该剖面保存了在白垩纪末期和古近纪两次爆发事件期间和之间的深部到上地壳的岩浆作用、变质作用和变形的记录。逆冲作用和深部沉积作用发生在较老耀斑的一部分，年轻耀斑的末期与深弧壳的折返同龄。研究人员将利用尖端的地球化学、地质年代学、温压测量和野外技术，研究弧内火成岩侵入体和变质沉积岩的组合，包括那些暴露在主要断裂系统中的岩石。这项研究的一个关键组成部分将是利用铀铅锆石地质/热年代学创建两次爆发事件期间岩浆添加的高时间分辨率记录，该记录可以直接与由铀-铅锆石、独居石和钛铁矿地质/热年代学相结合确定的变质作用、韧性变形和断层作用的类似记录进行比较，新石英在石榴石地质宝量表中的应用，以及传统的野外和微构造研究。这种方法将提供对岩浆爆发及其如何在100万年尺度上影响俯冲带地壳流变性的整体理解。特别是，首席调查员将讨论以下问题：减弱的深部地壳与爆发的岩浆活动之间的时间关系；围绕弧形的断裂系统相对于爆发变得活跃的时间；形变如何在不同的岩性和构造之间分配；在爆发期间是否以及何时发生地壳熔融；以及在爆发期间和在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，并通过开发和广告与拟议研究区域的路边地质相关的播客系列来创建一个长期的公共宣传计划，该研究区域位于罗斯湖国家娱乐区。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。