Collaborative Research: A Geochemical Approach to Quantifying the Magnitude of Strain and Fluid Flow along the Subduction Interface

合作研究：量化沿俯冲界面的应变和流体流动大小的地球化学方法

• 批准号: 2214324
• 负责人: Donald Fisher
• 金额: $ 51.86万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-07-15 至 2025-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2214324&HistoricalAwards=false
• 关键词: Collaborative; Research; Geochemical; Approach; Quantifying

Earth’s largest earthquakes occur along the megathrusts (the subduction plate interfaces) that separate rigid tectonic plates in subduction zones. The accumulation and release of elastic strain along these plate interfaces is predicated on the “healing” of the interface after the large earthquakes. This project will characterize the chemical and mechanical processes that control this healing during the time between earthquakes. Observations of ancient subduction interfaces, now exposed on land, will be used to inform a numerical model for slip and fluid flow. Together, these approaches will allow the investigators to determine how subduction zone processes impact the spatial and temporal patterns of earthquakes—an important step in assessing the hazards associated with active subduction zones. The study includes support for an early-career faculty member, a Ph.D. student, and nine undergraduates. Six of the undergraduates will be recruited from University of the Incarnate Word, an undergraduate body that serves a local Hispanic community.This project comprises a structural and geochemical investigation of two exhumed terrains that preserve a record of the physical and chemical conditions relevant to the plate interface of the global array of active subduction zones. Combined, the Shimanto belt in Japan and the Kodiak Accretionary complex in Alaska, form a composite record spanning depths from 8 to 20 km and peak temperatures between 150 and 350˚C. Electron-microscope-based elemental mapping of samples collected during several field campaigns will enable quantification of mineral phases and their redistribution with progressive strain. Combined cathodoluminescence mapping, electron backscatter diffraction, and fluid-inclusion microthermometry will constrain paleotemperatures and finite strain, and identify deformation mechanisms. Quantitative estimates of strain rate will be derived by combining strain magnitudes with field observations of shear zone thickness and present-day estimates of plate convergence rate. These measurements and observations will be used to inform a numerical model that parameterizes the effects of seismic slip, fluid flow and interseismic restrengthening on the temporal and spatial distribution of earthquakes on the plate interface. The multidisciplinary workplan is designed to address the following fundamental questions: Q1) What are the magnitudes of volume strain and shear strain associated with interseismic deformation? Q2) Is there a balance between dissolution along the scaly fabric and precipitation of minerals within cracks in blocks? Q3) What are the relative contributions to quartz vein formation of local diffusive mass transfer of silica versus the influx of dissolved silica by an externally derived fluid? Q4) How does partitioning of deformation mechanisms vary from the updip to the downdip ends of the seismogenic zone?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.

地球上最大的地震发生在俯冲带中分隔刚性构造板块的巨型逆冲断层上，这些板块界面上弹性应变的积累和释放取决于大地震后界面的“愈合”。将描述在地震之间控制这种愈合的化学和机械过程，对现在暴露在陆地上的古代俯冲界面的观测将被用来为滑移和流体流动的数值模型提供信息。这些方法将使研究人员能够确定俯冲带过程如何影响地震的空间和时间模式，这是评估与活动俯冲带相关的危害的重要一步。该研究包括对一名职业生涯早期的博士生的支持。学生和九名本科生将从化身大学招募，该大学是一个为当地西班牙裔社区服务的本科生机构。该项目包括对两个挖掘出的地形进行结构和地球化学调查，以保存物理记录。和相关的化学条件全球活跃俯冲带阵列的板块界面，日本的四万十带和阿拉斯加的科迪亚克增生杂岩体形成了跨越深度 8 至 20 公里、峰值温度在 150 至 350°C 之间的复合记录。对在几次现场活动中收集的样品进行基于显微镜的元素测绘将能够量化矿物相及其与渐进应变的组合的重新分布。衍射和流体包裹体显微测温将限制古温度和有限应变，并通过将应变大小与剪切带厚度的现场观测和当今板块收敛速率的估计相结合来确定应变速率的定量估计。观测结果将用于建立一个数值模型，该模型参数化地震滑移、流体流动和震间再强化对板块上地震时空分布的影响多学科工作计划旨在解决以下基本问题： Q1) 与震间变形相关的体积应变和剪切应变的大小是多少？ Q2) 沿鳞状结构的溶解与裂缝内矿物的沉淀之间是否存在平衡？ Q3) 二氧化硅的局部扩散传质与外部衍生流体的溶解二氧化硅的流入相比，对石英脉形成的相对贡献是什么？ Q4) 分配是如何进行的？变形机制从发震带的上倾端到下倾端各不相同？该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。