4-D Reconstruction of Magmatism at a long-lived Andesite Locus: Goat Rocks Volcanic Complex, Cascade Arc

以俯冲带为特色的大型复合火山是岩浆工厂的表面表现，岩浆工厂蒸馏地幔物质来创造和改变地壳。虽然火山本身对人类健康和财产构成危害，但驱动它们的岩浆系统导致用于电力和娱乐的热水循环，还导致在深处形成多种类型的矿藏。出于这些原因，俯冲火山的性质和发展以及提供它们的岩浆支撑是至关重要的。该项目将调查山羊岩火山群的长期(约300万年)发展，这是华盛顿喀斯喀特山脉的一群被侵蚀的复合火山群，以了解那里喷发的岩浆的来源和储存条件，以及它们如何随着时间的变化而变化。这项研究的更广泛的影响包括培训一名女博士生和本科生在不同的领域、实验室、出版和推广技能；与华盛顿自然资源部在项目和出版物上的合作；以及关于级联火山弧发展的动画。山羊岩火山杂岩是一个特别好的自然实验室，因为它很容易被冰川侵蚀暴露出来，它相对年轻，而且它跨越了俯冲带层状火山的全球组成范围的很大一部分。山羊岩火山杂岩的初步工作表明，岩浆系统在时间上发生了重大变化，从储存在地壳中等深度的富钾岩浆，到储存在更深处的低钾和更富水的岩浆。详细的地层学和地质年代学(主要是40Ar/39Ar测年)将为用于重建岩浆历史(例如压力、温度和水条件)的岩石和矿物的地球化学分析提供更可靠的时间框架，这将使用耦合质量和热平衡的计算机模型进行量化。然后将重建的这个火山杂岩与喀斯喀兹和其他弧区的其他俯冲火山的岩浆历史进行比较。一个特别的目的是评估相互冲突的岩浆生成和储存模式，即(1)普遍存在深部地壳岩浆产生的模式，在喷发前只有短暂的浅层储存；(2)如火山弧形地壳裸露部分所表明的那样，地壳和岩浆在各级之间广泛相互作用。我们假设，从发展的角度来看，这些模式可能会得到协调。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The large composite volcanoes that are distinctive of subduction zones are the surface expressions of the magma factory that distills mantle material to create and change the Earth’s crust. While the volcanoes themselves pose hazards to human health and property, the magma systems that drive them result in the circulation of hot water used for power and recreation, and also lead to the formation of many types of ore deposits at depth. For these reasons, the nature and development of subduction volcanoes and the magmatic underpinnings that feed them are critical. This project will investigate the long-term (~3 million year) development of the Goat Rocks Volcanic Complex, a cluster of eroded composite volcanoes in the Washington Cascade Range, to understand the origin and storage conditions of magmas erupted there and how they changed over time. Broader impacts of this study include the training of a female PhD student and undergraduate students in diverse field, laboratory, publication, and outreach skills; collaboration with the Washington Department of Natural Resources on projects and publications; and an animation of the development of the Cascade Volcanic Arc.The Goat Rocks Volcanic Complex makes a particularly good natural laboratory because it is well exposed by glacial erosion, it is relatively young, and it spans a large part of the global compositional range of subduction zone stratovolcanoes. Preliminary work at the Goat Rocks Volcanic Complex indicates that the magma system changed substantially in time, from potassium-rich magmas stored at modest depth in the crust, to low-potassium and more water-rich magmas stored at greater depth. Detailed stratigraphy and geochronology (mainly 40Ar/39Ar dating) will provide a more robust time framework for the geochemical analyses of rocks and minerals to be used in reconstructing the magmatic history (e.g., pressure, temperature and water conditions), which will be quantified using computer models that couple mass and thermal balance. The reconstruction of this volcanic complex will then be compared to the magmatic histories of other subduction volcanoes in the Cascades and in other arcs. A particular aim is to evaluate conflicting models of magma generation and storage, i.e. (1) a model wherein deep crustal magma generation is prevalent, with only transient shallow storage before eruption; vs. (2) extensive interaction between crust and magma at all levels, as suggested by exposed sections of volcanic arc crust. We posit that seen through the lens of development in time, such models may be reconciled.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.