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

含有高浓度二氧化硅的岩浆是地球上一些最具灾难性的喷发的原因，但在地壳中很少检测到它们。因此，人们对这些岩浆在喷发前的寿命和动力学知之甚少。就像树轮一样，这种岩浆中晶体的化学分带包含了岩浆演化的连续记录；与树轮不同，这种分带的实际意义被证明是难以捉摸的。特别是对于硅质岩浆，晶体尺度的分带剖面可能提供对岩浆历史的重要洞察。该项目将开发一种新校准的地质温度计，该温度计基于锆石的钛含量(Watson和Harison，2005)，目标是使用晶体分带来确定晶体历史上的大部分时间是悬浮在主要是液态岩浆中、孤立在堆积体中，还是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硅质火山活动中心(长谷、多巴和黄石)喷发的流纹岩，U-Th-Pb晶体年龄已经确定。由于这种新的地质温度计具有很高的地质应用潜力，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对温度计的影响。在结合所获得的年龄数据进行考虑时，将有可能确定破火山口硅质岩浆的时间-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是如何演化的，岩体增长的机制，以及地球大陆地壳的演化。这项研究将促进两个机构的研究人员和学生之间的合作，这两个机构为大量的少数民族学生提供服务，并将支持两个理科硕士的研究项目。学生和几个本科生。

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.