Magma Differentiation Time Scales in Carbonatite -Silicate Systems

智力优势。晶体、液体和蒸汽之间的相分离是岩浆多样化的最常见过程，也为岩浆如何凝固或喷发奠定了基础，但这种情况如何发生的确切机制仍然知之甚少。本研究的目的是限制空间相关的碳酸盐岩和硅酸盐岩浆的起源，并量化的时间尺度，在此期间，他们在一个浅岩浆系统相互作用。Laacher See火山是研究这些过程的理想场所：它是成分和热分区岩浆房的一个很好的研究例子，它喷发了一套显着的碳酸盐-硅酸盐捕虏体，为岩浆系统的晶体主导部分提供了见解。由于其年轻的年龄（喷发年龄12，900 a BP），可以应用U系列地质年代学，这将提供无与伦比的时间分辨率，约为10 E3 - 10 E4年。本研究拟采用二次电离质谱（西姆斯）、离子微探针（ion microprobe）对碳酸岩-正长岩捕虏体中的锆石进行U-Th同位素分析，以确定其结晶年龄及其与主要响岩岩浆的关系。锆石中的稀土元素和氧同位素组成也将用于追踪晶体起源（例如，原位形成或夹带捕虏晶）。最后，批量样品的U-Th同位素数据将被用来模拟碳酸盐岩和硅酸盐岩浆的分异时间，并检测老围岩的同化作用。这些数据将有助于了解岩浆分异的流体动力学时间尺度估计。Laacher See的研究结果最终将有助于更好地了解岩浆转移和储存的速率，以及地壳岩浆房中的质量和热量传输。Laacher See是一个潜在的仍然活跃的火山系统，位于人口稠密和工业化地区。这项研究将提高对这种差异化板内火山系统的行为和危害的理解。PI施密特是访问加州大学洛杉矶分校NSF国家离子微探针设施进行地质年代学或稳定同位素分析的主要研究人员。这些访问的科学家和研究生将直接受益于他们的研究项目，从方法上的进步与这个项目。该项目的国际合作（与哥廷根大学和日内瓦大学）为外国学生提供了在美国大学学习的经验。

Intellectual Merit. Phase separations between crystals, liquids, and vapor are the most common processes for magma diversification and also set the stage for how magmas solidify or erupt, yet the exact mechanisms of how this occurs remain poorly understood. The goal of this study is to constrain the origins of spatially associated carbonatite and silicate magmas and to quantify the time scales during which they interacted in a shallow magma system. Laacher See volcano is an ideal place to investigate these processes: it is a well studied example of a compositionally and thermally zoned magma chamber, and it erupted a remarkable suite of carbonatite - silicate xenoliths that provide insights into the crystal-dominated portions of the magma system. Because of its youthful age (eruption age 12,900 a BP), U-series geochronology can be applied which will provide unrivaled temporal resolution in the order of 10E3 -10E4 years. The proposed research will employ secondary ionization mass spectrometry (SIMS, ion microprobe) U-Th isotopic analysis of zircon from carbonatite - syenite xenoliths to determine their crystallization ages and their relation to the main phonolite magma. REE and oxygen isotopic compositions in zircon will also be used to trace crystal origins (e.g., formed in-situ or entrained xenocrysts). Finally, bulk sample U-Th isotope data will be used to model differentiation times for carbonatite and silicate magmas and to detect assimilation of older wall rocks. These data will contribute to understanding fluid-dynamic time scale estimates for magma differentiation. The results from Laacher See will ultimately contribute to an improved understanding of rates of magma transfer and storage, and mass and heat transport in crustal magma chambers.Broader Impact. Laacher See is a potentially still active volcanic system, located in a densely populated and industrialized region. This research will improve understanding of the behavior and hazards of such differentiated intraplate volcanic systems. PI Schmitt is the primary host of researchers that visit the NSF National Ion Microprobe Facility at UCLA for geochronological or stable isotope analyses. These visiting scientists and graduate students will directly benefit in their research projects from methodological advances related to this project. The international collaboration in this project (with Universities of Gottingen and Geneva) offers foreign students experience with universities in the US.