Sediment Recycling in Southern Cascadia: Insights From Seafloor Sediment and Mafic Volcanic Rock Geochemistry

该项目将调查海底沉积物和其他成分对南部喀斯喀特山脉岩浆喷发的贡献。在像卡斯卡迪亚这样的俯冲带板块边界，海洋板块下沉，或“俯冲”，进入大陆板块下方的地幔。俯冲的板块物质，包括海洋地壳和上覆海底沉积物的一部分，然后再循环到地幔中，并融入火山喷发的岩浆中，如喀斯喀特火山。这项研究将使用两个岩浆喷发在南部喀斯喀特山脉（从北方加州中部到俄勒冈州）和海底沉积物和海洋地壳近海南部喀斯喀特山脉的化学成分，以模拟沉积物和其他成分的贡献，岩浆。在这项研究中提供的沉积物再循环的估计将是重要的一系列研究卡斯卡迪亚俯冲带的科学家：这种再循环可以影响火山爆发的爆炸性和滑动在未来的地震卡斯卡迪亚板块边界。这个项目将解决三个关键问题，在南部卡斯卡迪亚俯冲物质的再循环：1）俯冲海底沉积物对南部喀斯喀特山脉岩浆喷发的贡献是什么？2)加入地幔的俯冲物质（洋壳、沉积物）的数量是多少？俯冲物质（流体和/或熔体）的性质是什么？（3）这些参数和其他重要参数（地幔成分、地幔熔融程度等）是如何影响地幔热演化的？沿着沿着弧线变化？为了回答这些问题，将对南部喀斯喀特海岸外戈尔达板块的海底沉积物和地壳的地球化学成分（主要和微量元素、同位素）以及玄武岩弧岩浆（包括挥发性成分）进行详细分析，并用于模拟每种潜在成分对岩浆的贡献。目前，卡斯卡迪亚南部近海沉积物的成分尚不清楚，无法直接评估它们对岩浆的贡献。由于这项研究，将有一个完整和连续的数据集的岩浆地球化学及其起源和成分的近海海底沉积物约450公里的卡斯卡迪亚。因此，当与以前的工作相结合的岩浆和他们的来源在其他部分的瀑布，这将是一个最好的研究弧世界各地，使大规模的俯冲和岩浆参数沿弧评估成为可能。

This project will investigate the contribution of seafloor sediments and other components to magmas erupted in the southern Cascades. In subduction zone plate boundaries like Cascadia, an oceanic plate sinks, or 'subducts', into the mantle beneath a continental plate. The subducted plate material, which includes oceanic crust and some portion of the overlying seafloor sediments, is then recycled into the mantle and incorporated into the magmas that erupt at volcanoes like those in the Cascades. This research will use the chemical compositions of both magmas erupted in the southern Cascades (from northern California through central Oregon) and the seafloor sediments and oceanic crust offshore of the southern Cascades to model the contributions of sediments, and other components, to the magmas. The estimates of sediment recycling provided in this research will be important to a range of scientists studying the Cascadia subduction zone: such recycling can impact the explosivity of volcanic eruptions and slip during future earthquakes at the Cascadia plate boundary.This project will address three key questions about recycling of subducted material in the southern Cascades: 1) What is the contribution of subducted seafloor sediment to magmas erupted in the southern Cascades?, 2) What is the quantity of subducted material (oceanic crust, sediment) added to the mantle, and what is the nature of that subducted material (fluid and/or melt)?, and 3) How do these and other important parameters (mantle compositions, extents of mantle melting, etc.) vary along the arc? To answer these questions, detailed analyses of the geochemical compositions (major and trace elements, isotopes) of seafloor sediments and crust from the Gorda plate offshore of the southern Cascades and basaltic arc magmas (including volatile contents) will be obtained and used to model the contributions of each potential component to the magmas. Currently, the compositions of sediments offshore of southern Cascadia are unknown, making direct assessment of their contributions to the magmas impossible. As a result of this research, there will be a complete and continuous dataset of the geochemistry of magmas and their origins and the compositions of offshore seafloor sediments for ~450 km of Cascadia. Thus, when combined with previous work on magmas and their sources in other portions of the Cascades, this will be one of the best-studied arcs worldwide, making large-scale along-arc assessments of subduction and magmatic parameters possible.