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

在俯冲带形成的熔体的地壳污染被广泛接受为在大陆地壳上形成的弧，但镁铁质地壳污染的潜在深刻和可能的神秘影响还没有得到很好的理解。拟议工作的智力价值是评估俯冲带上方地壳深部影响地幔岩浆上升的过程。北姐妹火山的喀斯喀特火山弧被选为这项研究，因为它是最不发达的（镁铁质）和最古老的成员的弧火山套件中的三个姐妹篇火山，并在一个异常的镁铁质弧段的原始，地幔的贡献受到限制。该研究的目标是：（1）确定构成North Sister玄武安山岩的区域独特的幔源玄武岩的成分多样性和比例;（2）评估这些地幔输入如何与地壳深部混合和相互作用;（3）限制岩浆过程发生的深度。为了实现这些目标，我们将结合联合收割机组成和同位素分析的岩石选择代表年龄和矿物光谱的熔岩采样过程中映射北姐妹火山。矿物及其熔融包裹体的微观分析将补充大块岩石分析，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的压力、温度和水条件。这项工作的更广泛影响包括对两名研究生进行实地、分析和实验技能培训，其中一名是女性，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。研究结果将在国家和国际会议上传播，并作为论文发表在权威期刊上。高压实验工作的技术开发和激光烧蚀熔融夹杂物分析将有助于科学基础设施。该项目是俄勒冈州和俄勒冈州大学之间精心设计的伙伴关系，利用互补的设施和调查专家的专业知识。拟议的工作也具有特别的社会效益，因为它涉及喀斯喀特火山弧特别活跃部分的火山历史，最近发现的隆起使人们关注潜在的火山危害。

JohnstonEAR-0230373 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.