Collaborative Research: Caldera Magmatism from the Inside Out: A geochronologic and Geochemical Investigation of Plutonic and Volcanic Rocks in Three Contrasting Calderas

合作研究：从内到外的火山口岩浆作用——对三个对比鲜明的火山口的深成岩和火山岩的地质年代学和地球化学研究。拟议的研究将利用同生火山岩和深成岩的地质年代学和地球化学来了解火山口岩浆作用的关键方面。在火山口岩浆活动期间，大量成分多样的岩浆被植入上地壳。这些岩浆的一部分喷发出来，其余的结晶形成岩体。我们目前对火山口岩浆过程的了解，大部分来自对火山岩的详细研究。同生深成岩还记录了有关火山口下岩浆过程的有用信息，如现有岩浆房的恢复和改造，岩脉和岩壁的就位，与复苏有关的上涌岩浆，以及岩浆作用的消退阶段。这些过程都没有直接记录在火山记录中。通过建立与火山口有关的火山岩和深成岩的时间、化学和空间关系，可以建立一个更全面的火山口岩浆活动模型。本文的研究目标包括：研究岩浆分异深度，探索岩浆侵入上地壳的速率，确定未喷发岩浆在火山口后岩浆活动中的作用，估算火山口岩浆房喷发的比例，确定分带和非分带火成岩套的差异，以及了解大体积硅质火山作用与深部作用的关系。三个中新生代破火山口系统——新墨西哥州的Questa和Organ以及科罗拉多州的Aetna火山——被选中用于研究与破火山口有关的岩浆作用。这些地区的大裂断作用暴露出了破火山口内的火山岩和破火山口下的侵入物。开发火山口岩浆作用模型的一个挑战是，不同火山口系统之间的过程可能不同。由于火山口岩浆作用的类型、暴露的火山和深部岩石的体积和深度不同，这些火山口系统为了解相关的岩浆作用提供了必要的多样性。过去几年的实地工作已经为每个地点提供了一套全面的样品。Ar-Ar方法将用于确定火山活动和岩体侵位的时间和冷却历史。激光烧蚀ICP-MS U-Pb测年将被用作鉴定样品的侦察工具，随后将使用CA-ID-TIMS方法确定样品的高精度年龄。利用离子探针o -同位素分析方法监测深成岩喷发后锆石的变质。同时期的深成岩和火山岩的地球化学将用于确定分馏、部分熔融和同化在产生大量硅熔体中的作用。更广泛的影响。了解与火山口相关的岩浆活动对于评估火山危害至关重要。综合火山口岩浆模型也可用于寻找与火山有关的地热活动和经济矿床。由于这项研究将为快速冷却的岩石（例如，火成岩，环状岩脉）产生高精度的UPb和Ar-Ar年龄，因此拟议的研究将测试最近为校准两种辐射测量系统所做的努力的准确性。该项目将为pi、两名博士生、两名硕士生和至少三名本科生提供新墨西哥理工大学、北卡罗来纳大学、美国地质调查局和加州大学洛杉矶分校之间的合作研究经验。研究将为研究生提供有用的实验室训练，以培养职业生涯所需的技能。在研究生的帮助下，pi将继续与国家和州立公园互动，为社区提供教育体验。数据将提交给NAVDAT数据库，该数据库曾经并将继续广泛用于发展本提案的核心思想。

Collaborative research: Caldera magmatism from the inside out - A geochronologic and geochemical investigation of plutonic and volcanic rocks in three contrasting calderasIntellectual Merit. The proposed research will use geochronology and geochemistry of cogenetic volcanic and plutonic rocks to understand critical aspects of caldera magmatism. During caldera magmatism, large volumes of compositionally diverse magmas are emplaced into the upper crust. Some fraction of this magma erupts and the remainder crystallizes to form a pluton. Much of our current understanding of caldera magmatic processes is from detailed studies of the vocanic rocks. Cogenetic plutonic rocks also record useful information about sub-caldera magmatic processes such as rejuvenation and modification of existing magma chambers, dike and sill emplacement, upwelling magma related to resurgence, and the waning stages of magmatism. None of these processes are directly recorded in the volcanic record. By establishing the temporal, chemical, and spatial relationship of both caldera-related volcanic and plutonic rocks, a more comprehensive model of caldera magmatism can be developed. Objectives of this proposal include investigating the depth of magma differentiation, exploring rates of magma emplacement into the upper crust, establishing the role of nonerupted magma in postcaldera magmatism, estimating the fraction of a caldera magma chambers that erupt, determining differences between zoned and nonzoned igneous suites, and understanding the relationship between large-volume silicic volcanism and plutonism. Three mid-Cenozoic caldera systems - Questa and Organ in New Mexico, and Mt. Aetna in Colorado, have been selected for investigating caldera related magmatism. Rio Grande-rift-faulting at these locations has exposed both intracaldera volcanic rocks and subcaldera intrusions. A challenge in developing caldera magmatism models is the likelihood that processes vary between different caldera systems. Because the field locations differ with respect to style of caldera magmatism and volume and depth of exposed volcanic and plutonic rocks, these caldera systems provide the necessary diversity to understand the associated magmatic processes. Fieldwork during the past several years has already yielded a comprehensive sample suite for each location. The Ar-Ar method will be used to establish the timing of volcanism and pluton emplacement and cooling histories. Laser ablation ICP-MS U-Pb dating will be used as a reconnaissance tool to identify samples for which high-precision ages will subsequently be determined using the CA-ID-TIMS method. Post-eruptive zircon modification in the plutonic rocks will be monitored using ion-probe O-isotope analysis. Geochemistry of coeval plutonic and volcanic rocks will be used to determine the roles of fractionation, partial melting, and assimilation in generating large volumes of silicic melt.Broader Impacts. Understanding the magmatism associated with calderas is essential to assessing volcanic hazards. Comprehensive caldera magmatic models may also be used to explore for volcanorelated geothermal activity and economic ore deposits. Because this study will produce high-precision UPb and Ar-Ar ages for rapidly cooled rocks (e.g. ignimbrites, ring dikes), the proposed research will test the accuracy of recent efforts to intercalibrate the two radiometric systems. The project will provide the PIs, two doctoral students, two masters students, and at least three undergraduate students a collaborative research experience between New Mexico Tech, the University of North Carolina, the USGS and UCLA. Research will provide graduate students with useful laboratory training to develop skills necessary for professional careers. The PIs, along with help from the graduate students, will continue interacting with national and state parks to provide an education experience for the community. Data will be submitted to the NAVDAT database, which was, and will continue to be, used extensively in developing the ideas central to this proposal.