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.

这个项目的目标是更好地了解岩浆是如何在地球内部产生的火山下面的喀斯喀特山脉的华盛顿，俄勒冈州和北方加州。 这一地区的火山活动是由俯冲过程引起的，在俯冲过程中，太平洋西北部近海的海洋地壳沉入地球。地幔沿着大陆边缘。 俯冲作用也是该地区可能发生的特大地震的原因。 当下沉的板块升温时，它释放出H2O和其他？挥发性？元素（Cl，S，F，C），这反过来又导致上覆的地幔岩石熔化，产生岩浆，为喀斯喀特火山提供燃料。 虽然俯冲过程发生在世界各地的许多地区（例如，安第斯山脉），喀斯喀特系统的一个显着特征是俯冲洋壳在开始俯冲时在地质上还很年轻。 这导致地壳变得更热，当俯冲地壳仍然很浅时，在它位于火山下面之前，应该会释放出H2O和其他挥发物。 主要的挑战，那么，是要了解什么样的作用H2O和其他挥发性物质在创造下面的喀斯喀特火山岩浆，如果挥发性物质是重要的，他们如何从俯冲洋壳回到地幔产生岩浆。暖板俯冲带，如瀑布弧。该项目将涉及对原始喀斯喀特岩浆中的H2O、其他挥发物、流体移动的元素以及稳定和放射性同位素示踪剂进行新的测量。许多测量将在熔融包裹体上进行，熔融包裹体是被困在深度生长的斑晶内的硅酸盐熔体的小斑点。 当岩浆向地球移动时，这种包裹体不受低压脱气的影响？的表面，从而提供了一个记录的喷发前溶解的挥发分含量的岩浆。 在这个项目中获得的数据将提供新的信息，地幔和板片温度，岩浆生产过程，以及在瀑布弧下的挥发物的来源。该项目涉及与美国其他科学家的合作，加拿大和日本进行一些专门的化学分析。 另一项合作工作将涉及对瀑布下的地幔楔流模式进行地球动力学建模，以便将新的地球化学数据与地球物理结果相结合。