Collaborative Research: Plutons as ingredients for continental crust: Pilot study of the differences between intermediate plutons and lavas in the intra-oceanic Aleutian arc

在整个相关的压力和温度范围内，在弧形中形成的长英质深成岩相对于地幔橄榄岩是浮力的。它们倾向于留在地球表面，形成大陆地壳的基本构造块。在阿留申山脉，大多数长英质深成岩的成分与对大陆地壳主体成分的估计重叠，与空间上伴生的熔岩明显不同。了解阿留申长英质深成岩的成因是通过弧形岩浆作用了解大陆成因和演化的关键，弧形岩浆作用是边缘和GeoPRISMS倡议的关键科学目标。PI将解决以下问题：(1)与附近的熔岩相比，阿留申深成岩是否具有不同的同位素来源成分？如果是这样的话，这一点至关重要，因为人们通常认为，喷发的玄武岩代表着从地幔到弧形地壳的岩浆流动。如果不是，我们将评估如何解释它们是同一亲本熔体上不同分化过程的结果。(2)随着时间的推移，阿留申弧内是否存在成分变化？深成岩和火山岩之间的差异是代表了弧形的时间演化，还是代表了不同岩浆成分的不同岩浆运输和侵位方式？(3)高粘度的长英质岩浆优先侵位在深成岩体中，而低粘度的镁铁质岩浆优先形成熔岩吗？当熔岩被认为是弧形岩浆过程和成分的代表时，这会带来什么偏见？更广泛的影响：阿留申弧会对社会造成许多危害。了解俯冲过程有助于预测、避免和/或减轻火山喷发、山体滑坡和地震的危险后果。在这个项目中，一名研究生将接受研究方面的培训，并很可能能够帮助设计和参与基于这个试点项目的更大的实地研究计划。

Felsic plutonic rocks formed in arcs are buoyant with respect to mantle peridotite over the entire range of relevant pressures and temperatures. They tend to remain at the Earth?s surface, to form the fundamental building blocks of continental crust. In the Aleutians, most felsic plutonic rocks have compositions that overlap estimates for the bulk composition of the continental crust, and that are distinctly different from spatially associated lavas. Understanding the genesis of Aleutian felsic plutonic rocks is a key to understanding continental genesis and evolution via arc magmatism, a key science goal for the MARGINS and GeoPRISMS Initiatives. The PIs will address the following questions: (1) Do Aleutian plutonic rocks have an isotopically distinct source composition, compared to nearby lavas? If they do, this is vitally important since it is commonly assumed that erupted basalts are representative of the magmatic flux from the mantle into arc crust. If not, we will evaluate how they can be explained as the result of different differentiation processes operating on the same parental melt. (2) Has there been compositional variation in the Aleutian arc over time? Do differences between plutonic and volcanic rocks represent temporal evolution of the arc, or different modes of magma transport and emplacement for different magma compositions? And (3) are high viscosity felsic magmas preferentially emplaced in plutons, while low viscosity, mafic magmas preferentially form lavas? What biases does this introduce, when lavas are presumed to be representative of arc magmatic processes and compositions?Broader Impacts: The Aleutian arc poses numerous hazards to society. Understanding subduction processes helps to predict, avoid, and/or mitigate the hazardous consequences of volcanic eruptions, landslides and earthquakes. During this project, a graduate student will be trained in research, and will likely be able to help design and participate in a larger field research program based on this pilot project.