Collaborative Proposal: North Sister Volcano: A Window into Deep Crustal Processes in a Mafic Arc

俯冲带熔体的地壳污染被广泛接受为在硅质大陆地壳上形成的弧，但基性地壳污染潜在的深刻和可能的隐性影响尚未得到很好的理解。所建议的工作的智力价值在于评估作用于俯冲带之上的地壳深处的过程，这些过程影响着从地幔上升的岩浆。本研究选择喀斯喀特火山弧的北姐妹火山，因为它是三姐妹火山中最不进化（基性）和最古老的弧火山组成员，并且位于一个异常基性的弧段，在那里原始的地幔贡献受到限制。研究的目的是：(1)确定有助于北姐妹玄武安山岩构造的具有区域特色的幔源玄武岩的组成种类和比例；(2)评估这些地幔输入如何与深部地壳混合和相互作用；(3)限制岩浆作用发生的深度。为了实现这些目标，我们将结合所选岩石的成分和同位素分析，以代表在绘制北姊妹火山期间采样的熔岩的年龄和矿物谱。矿物及其熔体包裹体的微量分析将补充整体岩石分析，以辨别岩浆历史。对天然样品的实验工作将揭示北姐妹岩浆形成时的压力、温度和水条件。这项工作的广泛影响包括对两名研究生进行实地、分析和实验技能的培训，其中一名研究生是女性，来自科学界代表性不足的群体。两名本科生也将获得研究机会。这项研究的结果将在国家和国际会议上传播，并作为论文在审定期刊上发表。高压实验工作和激光烧蚀熔体夹杂物分析技术的发展将有助于科学基础设施的建设。该项目是俄勒冈州立大学和俄勒冈大学之间精心设计的合作伙伴关系，利用互补的设施和研究者的专业知识。拟议的工作也具有特殊的社会效益，因为它解决了喀斯喀特弧特别活跃部分的火山历史，最近发现的隆起引起了人们对潜在火山危害的关注。

GrunderEAR-0230359 Crustal contamination of melts formed in subduction zones is widely accepted for arcs formed on silicic continental crust, but the potentially profound and likely cryptic effects of contamination by mafic crust are not well understood. The intellectual merit of the proposed work is the assessment of processes acting in the deep crust above a subduction zone that affect the magmas rising from the mantle. North Sister volcano of the Cascades volcanic arc is selected for this study because it is the least evolved (mafic) and oldest member of an arc volcano suite represented in the Three Sisters volcanoes, and lies in an unusually mafic segment of arc where the primitive, mantle contributions are constrained. The study's objectives are (1) to identify the compositional variety and proportion of regionally distinctive mantle-derived basalts that contributed to the construction of the basaltic andesite at North Sister; (2) to evaluate how these mantle inputs mix and interact with the deep crust; and (3) to constrain the depth at which the magmatic processes took place. To achieve these goals we will combine compositional and isotopic analysis of rocks selected to represent the age and mineralogical spectrum of lavas sampled during the course of mapping North Sister Volcano. Microanalysis of minerals and their melt inclusions will supplement the bulk rock analyses to discern magmatic histories. Experimental work on natural samples will reveal the pressure, temperature and water conditions under which the North Sister magmas formed. The broader impact of this work includes training in field, analytical and experimental skills of two graduate students, one of which is female and from an underrepresented groups in science. Two undergraduates will also be given research opportunities. The results of the study will be disseminated at national and international meetings and as papers in refereed journals. Technique development for high-pressure experimental work and melt inclusion analysis by laser ablation will contribute to scientific infrastructure. The project is a carefully crafted partnership between Oregon State and University of Oregon taking advantage of complementary facilities and investigator expertise. The proposed work is also of particular societal benefit as it addresses the history of a volcano that is in a particularly active part of the Cascades arc, where recently identified uplift has focused attention on potential volcanic hazards.