Identifying Crustal and Mantle Processes in the Central Trans-Mexican Volcanic Belt

学术价值：俯冲带是地球上许多活跃的火山爆发和相关危险的场所，也是地壳和地幔之间物质交换的重要场所，是大陆地壳生长和地壳-地幔系统随时间演变的基本因素。爆炸性的硅质层状火山引起了很多关注，但对基性单成因火山的研究却很少，它们非常常见，而且具有很高的破坏性。此外，它们的基性组成使它们成为研究俯冲背景下地幔过程的理想材料。我们建议对跨墨西哥火山带中部历史上的Jorullo和Parícutin单成因火山中心进行详细的多同位素研究。约鲁洛火山和Parícutin火山是理想的成对案例研究，因为：它们都产生了有详细记录的历史喷发；已经进行了详细的实地研究，以便选择用于地球化学分析的样品可以放在地层环境中；两者均表现出SiO2随时间增加的时间组成趋势，这在基性单成因喷发中很常见，但其成因尚不清楚；它们代表了推断出的地壳相互作用程度的可能端元，Jorullo熔岩污染较少，Parícutin熔岩污染非常广泛；现有的局部上下地壳捕虏体将允许对岩石圈同化作用进行严格的研究；在相对固定的构造/地质背景下，不同火山中心的地幔和地壳过程的潜在变异性可以进行比较。Sr- nd - pb - hf -Os同位素组成将在整个岩石的熔岩、火山体和地壳包体中测量，O和Os同位素在橄榄石-氧化物基质分离物中测量，Sr同位素在单个熔融包裹体中测量。这些数据将独特地限制下地壳和上地壳同化的相对作用，以及地幔楔中可能添加的板块衍生成分，包括含水板块流体和沉积物熔体。这项研究将对基性单成因火山系统中岩浆储层的建立和喷发产物的时间组成变化的原因具有重要意义，并将对地幔楔内小空间尺度上板源流体/熔体的性质和非均质性提供见解。更广泛的影响：学生培训和教育：参与该项目的学生将在几种最先进的分析技术方面获得丰富的经验，并且至少有一名学生将参加实地工作，接受实地火山学方面的培训。预计实地工作将与火山学实地讲习班一起进行，为更多的学生提供受益的机会。这项研究的结果也将被纳入课堂的讲座材料和相关的实践，探究式学习活动。为科学领域的女性提供指导：智慧是科学领域女性的榜样/导师，目前有一个由4名女性博士生组成的研究小组。Widom和她的学生过去一直与本科生密切合作，预计以女性为主的研究小组将有助于吸引女性本科生的参与。外联活动：该项目将与冯·洪堡基金会最近向Siebe和Schmincke提供的赠款密切相关，其中实地测绘和火山学研究的结果以及我们新的地球化学数据将与Jorullo作为新的联合国教科文组织地质公园的建立相结合。此外，Widom和她的学生将通过迈阿密大学参与外展项目，包括担任迈阿密Limper地质博物馆的顾问，通过博物馆的K-12项目为社区提供基于研究的教育体验，以及为当地退休人员和社区大学生提供实验室参观/演示。火山危害评估：该项目的结果将有助于限制位于一个高度活跃的火山地区的两座历史火山的喷发前过程，在这些火山地区，任何未来的喷发都将对当地人口和包括莫雷利亚和可能的墨西哥城在内的主要城市中心产生重大影响。国际合作：该项目将促进与墨西哥地质学家Siebe和Schaaf以及德国火山学家Schmincke的持续国际合作。该奖项由国际科学与工程办公室（OISE）共同资助。

Intellectual Merit: Subduction zones are the sites of much of the Earth's active explosivevolcanism and associated hazards, and also important sites of mass exchange between the crust and mantle, and fundamental agents in the growth of the continental crust and evolution of the crust-mantle system through time. Much attention has been focused on explosive silicicstratovolcanoes, yet less studied mafic monogenetic cones are very common and can be highly destructive. In addition, their mafic composition makes them ideal for study of mantle processes in subduction settings. We propose to do a detailed multi-isotopic study of the historic Jorullo and Parícutin monogenetic volcanic centers in the central Trans-Mexican Volcanic Belt. Jorullo and Parícutin volcanoes are ideal for a paired case study because: they both produced well documented historic eruptions; detailed field studies have been done so samples selected for geochemical analysis can be placed in stratigraphic context; they both exhibit a temporal compositional trend of increasing SiO2 with time that is common in mafic monogenetic eruptions but the origin of which is poorly understood; they represent possible endmembers in inferred extents of crustal interaction, with lesser contamination of Jorullo lavas and very extensive contamination of Parícutin lavas; existing local upper and lower crustal xenoliths will allow rigorous investigation of the role of lithospheric assimilation; and their close geographic proximity enables a comparison of potential variability of mantle and crustal processes in different volcanic centers in a relatively fixed tectonic/geologic setting. Sr-Nd-Pb-Hf-Os isotopic compositions will be measured on whole-rock lavas, tephra, and crustal xenoliths, O and Os isotopes on olivine-oxide-matrix separates, and Sr isotopes in single melt-inclusion-bearing olivines. These data should uniquely constrain the relative roles of lower and upper crustal assimilation and the potential addition of slab-derived components to the mantle wedge including hydrous slab-fluid and sediment-melt. This study will have important implications regarding the establishment of magma reservoirs in mafic monogenetic volcanic systems and the cause of temporal-compositional variations in eruptive products, and will provide insights into the nature and heterogeneities of slab-derived fluids/melts over small spatial scales within a mantle wedge.Broader Impacts: Student Training & Education: Students involved in this project will gain extensive experience in several state-of-the-art analytical techniques, and at least one student will participate in fieldwork, receiving training in field volcanology. It is anticipated that the field work will be done in conjunction with a volcanology field workshop, providing the opportunity for additional students to benefit. Results from this research will also be incorporated into the classroom in lecture material and related hands-on, inquiry-based learning activities. Mentoring Women in Science: Widom serves as a role model/mentor for women in science, and currently has a research group with 4 female Ph.D. students. Widom and her students have worked closely with undergraduates in the past, and it is anticipated that the female-dominated research group will help attract participation of female undergraduate students. Outreach Activities: This project will be closely linked to the recent von Humboldt Foundation grant to Siebe and Schmincke, in which results of field mapping and volcanological studies, and our new geochemical data, will be integrated with the establishment of Jorullo as a new UNESCO GeoPark. In addition, Widom and her students will be involved in outreach programs through Miami U, including serving as consultants with Miami's Limper Geology Museum and providing research-based educational experiences to the community through the museum's K-12 programs as well as lab tours/demonstrations to local retirees and community college students. Volcanic Hazard Assessment: The results of this project will help constrain pre-eruptive processes in two historic volcanoes in a highly active volcanic region in which any future eruption will have a major impact on the local population and major urban centers including Morelia and likely Mexico City. International Collaboration: This project will foster ongoing international collaborations with Mexican geologists Siebe and Schaaf, as well as German volcanologist Schmincke.This award is co-funded by the Office of International Science and Engineering (OISE).