Collaborative Research: Crystal-Scale Histories of Magma Evolution from Zircon T-X-t

合作研究：锆石 T-X-t 的晶体尺度岩浆演化历史

• 批准号: 0538309
• 负责人: Mary Reid
• 金额: $ 11.99万
• 依托单位: Northern Arizona University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-06-01 至 2012-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0538309&HistoricalAwards=false
• 关键词: Collaborative; Research; Crystal; Scale; Histories

Magmas containing high concentrations of SiO2 are responsible for some of the most catastrophic eruptions on Earth yet they are rarely detected in the crust. Consequently, little is known about the longevity and dynamics of such magmas prior to their eruption. Much like tree-rings, the chemical zoning of crystals in such magmas contain a sequential record of magmatic evolution; unlike tree-rings, unraveling the practical significance of this zoning has proved to be elusive. For silicic magmas in particular, crystal-scale zoning profiles may provide essential insights into magmatic history. This project will exploit a newly calibrated geothermometer that is based on the titanium content of zircons (Watson and Harrison, 2005) with the goal of using crystal zoning to determine whether crystals spend much of their history suspended in mostly liquid magma, isolated in cumulates piles, or solidified as a part of granitoids. The work will initially focus on rhyolites erupted at three important centers of silicic volcanism (Long Valley, Toba, & Yellowstone) for which U-Th-Pb crystal ages have already determined. Because this new geothermometer has a high potential for many geologic applications, ion microprobe trace element analyses of the zircons will be performed in order to evaluate how crystal growth kinetics, crystal-melt partitioning, and magma mixing might affect the thermometer. When considered in the context of the age data obtained, it will be possible to delimit the time-temperature-compositional evolution of silicic magmas at caldera volcanoes. It is expected that the results will provide a better understanding of how silicic magmas evolve prior to eruption, the mechanisms of pluton growth, and the evolution of Earth's continental crust. The research will engender collaboration between researchers and students at two institutions that serve significant numbers of ethnic minority students, and will support the research projects of two M.Sc. students and several undergraduates.

含有高浓度二氧化硅的岩浆是地球上一些最灾难性的火山喷发的原因，但它们在地壳中很少被发现。 因此，人们对此类岩浆喷发前的寿命和动态知之甚少。 与树木年轮非常相似，此类岩浆中晶体的化学分区包含岩浆演化的连续记录。与树木年轮不同，阐明这种分区的实际意义已被证明是难以捉摸的。 特别是对于硅质岩浆，晶体尺度的分区剖面可以为岩浆历史提供重要的见解。 该项目将利用一种新校准的地温计，该地温计基于锆石的钛含量（Watson 和 Harrison，2005），目的是利用晶体分区来确定晶体是否在其历史的大部分时间里悬浮在主要是液态的岩浆中，并隔离在堆积堆中，或凝固为花岗岩的一部分。 这项工作首先将重点关注在三个重要的硅质火山活动中心（长谷、多巴和黄石）喷发的流纹岩，这些火山的 U-Th-Pb 晶体年龄已经确定。 由于这种新型地温计在许多地质应用中具有很高的潜力，因此将对锆石进行离子微探针痕量元素分析，以评估晶体生长动力学、晶体熔体分配和岩浆混合可能如何影响温度计。 当结合所获得的年龄数据进行考虑时，将有可能界定破火山口火山硅质岩浆的时间-温度-成分演化。 预计这些结果将有助于更好地了解硅质岩浆在喷发前如何演化、岩体生长机制以及地球大陆地壳的演化。 该研究将促进两个为大量少数民族学生提供服务的机构的研究人员和学生之间的合作，并将支持两个硕士学位的研究项目。学生和数名本科生。