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

地球上最大的地震发生在巨型逆冲断层（俯冲板块界面）上，它将俯冲带中的刚性构造板块分开。沿这些板块界面的弹性应变的积累和释放是基于大地震后界面的“愈合”。该项目将描述在两次地震之间控制这种愈合的化学和机械过程。对古代俯冲界面的观测，现在暴露在陆地上，将用于为滑动和流体流动的数值模型提供信息。总之，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。这项研究包括对一名早期职业教师、一名博士生和九名本科生的支持。其中六名本科生将从圣道大学（University of the Incarnate Word）招募，这是一个为当地西班牙裔社区服务的本科机构。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，这些地形保存了与全球活动俯冲带阵列的板块界面相关的物理和化学条件的记录。结合日本的Shimanto带和阿拉斯加的Kodiak增生杂岩，形成了一个复合记录，深度从8到20公里，峰值温度在150到350˚C之间。在几次野外活动中收集的样品的基于电子显微镜的元素测绘将能够量化矿物相及其随渐进应变的重新分布。结合阴极发光作图、电子背散射衍射和流体包裹体显微测温，可以约束古温度和有限应变，识别变形机制。应变率的定量估计将通过结合应变量级与剪切带厚度的现场观测和目前对板块收敛速率的估计而得出。这些测量和观测将用于建立一个数值模型，该模型将参数化地震滑动、流体流动和震间再强化对板块界面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)沿着鳞状结构的溶解和块状裂缝中矿物质的沉淀之间是否存在平衡？Q3)二氧化硅局部扩散传质与外源流体溶解二氧化硅流入对石英脉形成的相对贡献是什么？Q4)在孕震带的上、下倾两端，变形机制的划分有何不同？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。

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.