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

在整个相关压力和温度范围内，弧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上？形成大陆地壳的基本组成部分。在阿留申群岛，大多数长英质深成岩的成分与大陆地壳的整体成分重叠，与空间相关的熔岩明显不同。了解阿留申长英质深成岩的成因是了解大陆弧岩浆作用的成因和演化的关键，而弧岩浆作用是边缘和地球地质活动的一个重要科学目标。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同位素不同的源成分？如果确实如此，这一点至关重要，因为人们通常认为喷发的玄武岩代表了从地幔进入弧壳的岩浆流。如果没有，我们将评估如何将它们解释为在同一母熔体上运行的不同分化过程的结果。(2)随着时间的推移，阿留申弧的成分是否发生了变化？深成岩和火山岩的差异是否代表了弧的时间演化，还是代表了不同岩浆成分的不同岩浆搬运和侵位方式？(3)黏度高的长英质岩浆是否优先嵌入岩体，而黏度低的基性岩浆是否优先形成熔岩？当熔岩被认为是弧岩浆过程和成分的代表时，这会带来什么偏差？更广泛的影响：阿留申弧对社会造成了许多危害。了解俯冲过程有助于预测、避免和/或减轻火山爆发、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，并有可能帮助设计和参与基于这个试点项目的更大的实地研究项目。

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.