CAREER: Shallow angle subduction and tectonic underplating of magmatic arc root zones: a recipe for high-flux magmatism?

该项目评估了一种假设，即大陆下方的物质以浅角度俯冲，并将这些物质粘在上覆板块的底部，可能导致火成岩活动的“爆发”（即更大规模的火山爆发和地下侵入）。这一假说预测，俯冲作用应该先于上板块火成岩活动的上升，而上板块岩浆活动应该在空间上与下镀区域重叠。为了验证这一假设，本研究将重点放在两个与俯冲有关的岩石位于火山-深部物质下面的地点：克拉马斯山脉（加利福尼亚北部-俄勒冈南部）和加利福尼亚中部海岸山脉。这项工作有可能改变对浅角俯冲与上板块岩浆作用之间关系的认识。这项研究解决了一个具有全球意义的问题，即浅角度俯冲是大陆地壳的净生产者还是破坏者，这对地壳如何随时间增长（或收缩）有影响。该项目：1)为大约54名学生提供基于实地的研究经验和师生之间以及同侪之间的指导，增加了这些学生在STEM（科学、技术、工程和数学）领域继续学习和职业的可能性；2)每年向美国各地的现代分析技术和活跃的研究人员展示两名未被充分代表的少数民族本科生研究人员和一名学士学位后研究人员；3)加速首席研究员作为教师学者的职业发展，建立新的和加强现有的合作；4)制作招聘和宣传材料，旨在提高STEM领域中代表性不足群体的知名度；5)在明尼苏达州双城地区的小学生中开展积极的推广项目。本项目旨在通过对系统输入（例如构造和岩浆底沉积）和输出（构造侵蚀和分层）的调查和质量平衡，阐明控制大陆地壳长期稳定性的过程。浅角度（即倾角小于30度）俯冲的地点约占活动俯冲带的10%，是本项目的特别重点，因为这些地区具有快速地壳生长和破坏的特征。例如，熔体肥沃的弧前物质可能在板块变浅过程中被输送到弧根区，为上覆板块的高通量岩浆活动提供了可能的催化剂。考虑到这一点，本工作的研究目的是验证这样一种假设，即在浅层俯冲事件期间，弧前物质直接位于活动弧下的构造底板可以在弧关闭之前触发高通量岩浆活动。本研究的科学价值包括：1)有可能改变我们对浅层俯冲、构造底板和弧岩浆作用之间关系的认识；2)限定发掘出的浅层俯冲系统的构造侵蚀和底沉积速率，以便与现代系统进行比较；3)厘清加州海岸山脉中部和克拉马斯山脉中部的原始位置和岩性对比。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project evaluates the hypothesis that shallow-angle subduction of material beneath a continent, and sticking that material to the base of the overriding plate, can cause a "flare-up" in igneous activity (i.e., more voluminous volcanic eruptions and subsurface intrusions). This hypothesis predicts that subduction should shortly precede an uptick in upper plate igneous activity and that upper plate magmatism should spatially overlap the underplated region. To test this hypothesis, this research focuses on two sites where subduction-related rocks underlie volcanic-plutonic materials: the Klamath Mountains (northern California-southern Oregon) and the central California Coast Ranges. This work has the potential to transform understanding of the relationships between shallow-angle subduction and upper plate magmatism. This research addresses the globally significant question of whether shallow-angle subduction is a net producer or destroyer of continental crust, which has implications for how the crust grows (or shrinks) over time. This project: 1) provides a field-based research experience and instructor-student and peer-student mentoring for approximately 54 students, increasing the likelihood that these students will pursue continued study and careers in the STEM (science, technology, engineering and mathematics) fields; 2) exposes two underrepresented minority undergraduate researchers and one post-baccalaureate researcher per year to modern analytical techniques and active researchers across the United States; 3) accelerates the career development of the principal investigator as a teacher-scholar, building new and enhancing existing collaborations; 4) produces recruitment and promotional materials aimed at increasing the visibility of underrepresented groups in STEM fields; and 5) sustains an active outreach program with elementary school students of the greater Twin Cities, Minnesota region. This project aims to clarify the processes that control the long-term stability of continental crust through investigation and mass balance of system inputs (e.g., tectonic and magmatic underplating) and outputs (tectonic erosion and delamination). Sites of shallow angle (i.e., a dip of less than 30 degrees) subduction, representing about 10% of active subduction zones, are a particular focus of this project, as rapid crustal growth and destruction characterize these areas. For example, melt-fertile forearc materials are likely conveyed into arc root zones during the slab shallowing process, providing a possible catalyst for high-flux magmatism in the overriding plate. With this in mind, the research objective of this work is to test the hypothesis that tectonic underplating of forearc materials directly beneath active arcs during shallow subduction events can trigger episodes of high-flux magmatism prior to arc shutoff. The scientific merits of this research include: 1) the potential to transform our understanding of the relationships between shallow subduction, tectonic underplating, and arc magmatism; 2) constraining the rates of tectonic erosion and underplating in exhumed shallow subduction systems for comparison with modern systems; and 3) clarifying the original positions of, and lithologic correlations within, the central California Coast Ranges and the central Klamath Mountains.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.