Collaborative Research: The Time Scales of Magmatic Differentiation and Their Relationship to Eruptive Style

冰岛南部的赫克拉火山在火山活动方式和岩石演化程度上具有明显的对应关系。大多数喷发都是分区的，特别是那些打断长时间休眠的喷发，以爆炸性硅质相开始，以镁铁质冰洲岩的渗出结束。Thorarinsson的开创性工作表明，Hekla的分化程度与喷发之间的休息有关。该项目旨在详细研究历史喷发的分区产物，以阐明分异的机制和时间尺度。将进行实地工作，以收集每次历史喷发的样品序列;因为喷发都是历史性的，结晶、混合和分化的最短时间受到很好的限制。将使用现代最先进的技术对每种岩石进行分析，但这项研究的重点是斑晶相的微观分析，斑晶相是它们结晶的液体成分的示踪剂。斑晶的主量和微量元素分带剖面和熔体包裹体分析将有助于确定斑晶的母体，以及它们被夹带在其寄主岩浆中的持续时间。斑晶的氧同位素比值和熔融包裹体的水分析记录了水对岩浆演化的影响程度。最后，对斑晶进行相对短寿命的锕系同位素分析将限制它们的年龄，即它们在岩浆管道系统中存在的时间。就更广泛的影响而言，该奖项将支持爱达荷州大学的一名博士生和高露洁大学的六名本科生的研究工作。PI设计了一个计划，为博士生提供长期与本科生一起工作的教学和指导经验。反过来，高露洁的学生将有机会参加扩展的实地考察，与研究科学家互动，研究独立的，有针对性的研究问题。研究结果还将纳入高露洁和爱达荷州大学的本科和研究生课程，以及旨在为当地K-12学生和社区团体带来实践科学调查的推广计划。

Hekla volcano in southern Iceland displays a remarkable correspondence between its style of volcanic activity and extent of petrologic evolution. Most eruptions are zoned, especially the ones that punctuate long repose, initiating with an explosive siliceous phase and ending with effusion of mafic icelandite. The pioneering work of Thorarinsson showed that the extent of differentiation at Hekla correlates with the repose between eruptions. This project is designed to study in detail the zoned products of the historical eruptions, in order to elucidate the mechanisms and timescales of differentiation. Field work will be conducted in order to collect sequences of samples from each historical eruption; because the eruptions are all historical, the minimum time for crystallization, mixing, and differentiation is well-constrained. Each of the rocks will be analyzed using modern, state of the art techniques, but the focus of this study is microanalysis of phenocryst phases, which are tracers of the liquid compositions from which they crystallized. Major and trace element zoning profiles of phenocrysts and analyses of melt inclusions will help determine the parentage of the phenocrysts, as well as the duration they have been entrained in their host magmas. Oxygen isotopic ratios of the phenocrysts and water analyses of melt inclusions record the extent to which water influences magmatic evolution. Finally, relatively short-lived actinide-series isotopic analyses of the phenocrysts will constrain their age, the amount of time they have resided in the magmatic plumbing system. In terms of broader impacts, this award will support the research endeavors of a doctoral student at the University of Idaho and six Colgate University undergraduates. The PIs have designed a plan to provide the PhD student with teaching and mentoring experience working with the undergraduates on a protracted basis. The Colgate students, in turn, will have the opportunity to participate in extended fieldwork, interact with research scientists, work on independent, focused research questions. Results will also be incorporated into both undergraduate and graduate level courses at Colgate and the University of Idaho, as well as outreach programs designed to bring hands-on science investigation to local K-12 students and community groups.