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SiO2的岩浆是地球上一些最灾难性的火山爆发的原因，但它们很少在地壳中被检测到。 因此，人们对这种岩浆在喷发前的寿命和动力学知之甚少。 就像树木年轮一样，这种岩浆中晶体的化学分带包含了岩浆演化的连续记录;与树木年轮不同，揭示这种分带的实际意义已被证明是难以捉摸的。 特别是对于岩浆，晶体尺度的分区配置文件可以提供必要的见解岩浆的历史。 该项目将利用一种新校准的地质温度计，该温度计以锆石的钛含量为基础（沃森和哈里森，2005年），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，孤立地堆积在堆积物中，或作为花岗岩类的一部分固化。 这项工作最初将集中在三个重要的火山活动中心（长谷，多巴，黄石）的U-Th-Pb晶体年龄已经确定的流纹岩喷发。 由于这种新的地质温度计具有很高的潜力，许多地质应用，离子微探针微量元素分析的锆石将进行，以评估晶体生长动力学，晶体熔体分配，岩浆混合可能会影响温度计。 当考虑到所获得的年龄数据的背景下，它将有可能界定的时间-温度-成分的火山口火山岩浆的演变。 预计这些结果将有助于更好地了解岩浆在喷发前的演化、深成岩的生长机制以及地球大陆地壳的演化。 这项研究将在两个为少数民族学生提供大量服务的机构的研究人员和学生之间产生合作，并将支持两名硕士学生和几名本科生的研究项目。