Testing Models of Magma Generation in Warm-slab Subduction Zones: A Case Study of Volatiles in the Cascade Arc

暖板俯冲带岩浆生成模型测试：以喀斯喀特弧挥发物为例

• 批准号: 1119224
• 负责人: Paul Wallace
• 金额: $ 29.53万
• 依托单位: University of Oregon Eugene
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-07-01 至 2015-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1119224&HistoricalAwards=false
• 关键词: Testing; Models; Magma; Generation; Warm

The goal of this project is to better understand how magma is produced inside the Earth beneath the volcanoes in the Cascade mountains of Washington, Oregon, and northern California. Volcanism in this region is caused by the process of subduction, in which oceanic crust offshore of the Pacific northwest sinks back into the Earth?s mantle along the continental margin. Subduction is also responsible for the very large earthquakes that can occur in this region. As the sinking plate heats up, it releases H2O and other ?volatile? elements (Cl, S, F, C), which in turn cause the overlying mantle rocks to melt, producing magma that feeds the Cascade volcanoes. While the process of subduction occurs in many regions around the world (e.g., the Andes), a distinctive feature of the Cascades system is that the subducted oceanic crust is geologically young when it starts to subduct. This causes the crust to be hotter and should result in release of H2O and other volatiles when the subducted crust is still quite shallow, before it lies beneath the volcanoes. The main challenge, then, is to understand what role H2O and other volatiles play in creating magma beneath the Cascade volcanoes, and if volatiles are important, how they move from the subducted oceanic crust back into the mantle to produce magma.This project will test some fundamental ideas about volatile recycling and magma generation in ?warm-slab? subduction zones such as the Cascades arc. The project will involve new measurements of H2O, other volatiles, fluid mobile elements, and stable and radiogenic isotope tracers in primitive Cascade magmas. Many of the measurements will be done on melt inclusions, which are small blobs of silicate melt trapped inside of growing phenocrysts at depth. Such inclusions are not affected by low pressure degassing as magma moves towards the Earth?s surface, and thus provide a record of the pre-eruptive dissolved volatile contents in magma. The data obtained in this project will provide new information on mantle and slab temperatures, magma production processes, and the sources of volatiles beneath the Cascades arc. This project involves collaborations with other scientists in the U.S., Canada, and Japan for some of the specialized chemical analyses that will be done. Another collaborative effort will involve geodynamic modeling of mantle wedge flow patterns beneath the Cascades so the new geochemical data can be integrated with geophysical results.

该项目的目的是更好地了解如何在华盛顿，俄勒冈州和北加州喀斯喀特山脉的火山下方生产岩浆。 该地区的火山主义是由俯冲过程引起的，俯冲的过程中，太平洋西北部的海洋壳沿着大陆边缘沿着大陆沿着地球倒入地球。 俯冲还导致该地区可能发生的非常大的地震。 当沉没板加热时，它会释放H2O和其他挥发性？元素（Cl，S，F，C）又导致地面岩石融化，产生岩浆，以供应级联火山。 俯冲过程发生在世界各地的许多地区（例如，安第斯山脉），但级联系统的独特特征是，俯冲的海洋壳在开始俯冲时在地质上是年轻的。 这会导致外壳更热，并且当俯冲的外壳仍然很浅时，在火山下仍然很浅时，应导致H2O和其他挥发物的释放。 因此，主要的挑战是要了解H2O和其他挥发物在喀斯喀特火山下创建岩浆中的作用，如果挥发物很重要，它们如何从俯冲的海洋壳中转移到地幔中产生岩浆，以生产岩浆，以测试有关挥发性回收和岩浆生成的一些基本观念？俯冲带，例如级联电弧。该项目将涉及H2O，其他挥发物，流体移动元件以及原始级联岩浆中的稳定和放射同位素示踪剂的新测量。许多测量将对熔体夹杂物进行，这些熔体是在深度生长的表晶中捕获的硅酸盐熔体的小斑点。 当岩浆向地球表面移动时，这种夹杂物不受低压脱气的影响，因此提供了岩浆中喷发前溶解的挥发性含量的记录。 该项目中获得的数据将提供有关地幔和板温度，岩浆生产过程以及级联弧下挥发物来源的新信息。该项目涉及与美国，加拿大和日本的其他科学家合作进行一些专门的化学分析。 另一个协作的工作将涉及层层下地幔楔流模式的地球动力学建模，因此可以将新的地球化学数据与地球物理结果集成在一起。