Magma Differentiation Time Scales in Carbonatite -Silicate Systems

碳酸岩-硅酸盐体系中岩浆分异时间尺度

• 批准号: 0711193
• 负责人: Axel Schmitt
• 金额: $ 9.04万
• 依托单位: University of California-Los Angeles
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-08-01 至 2009-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0711193&HistoricalAwards=false
• 关键词: Magma; Differentiation; Time; Scales; Carbonatite

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.

智力优点。晶体、液体和蒸汽之间的相分离是岩浆多样化最常见的过程，也为岩浆凝固或喷发奠定了基础，但其发生的确切机制仍知之甚少。这项研究的目的是限制空间相关的碳酸岩和硅酸盐岩浆的起源，并量化它们在浅层岩浆系统中相互作用的时间尺度。拉赫湖火山是研究这些过程的理想场所：它是一个经过充分研究的岩浆室成分和热区的例子，它喷发了一套引人注目的碳酸岩-硅酸盐捕虏体，为了解岩浆系统中以晶体为主的部分提供了见解。由于其年龄较年轻（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 10E3 -10E4 年。拟议的研究将采用二次电离质谱法（SIMS，离子微探针）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，原位形成或夹带的异晶）。最后，大量样品 U-Th 同位素数据将用于模拟碳酸岩和硅酸盐岩浆的分化时间，并检测较老围岩的同化作用。这些数据将有助于理解岩浆分化的流体动力学时间尺度估计。 Laacher See 的结果最终将有助于更好地了解岩浆转移和储存的速率，以及地壳岩浆室中的质量和热量传输。更广泛的影响。拉彻湖 (Laacher See) 是一个可能仍然活跃的火山系统，位于人口稠密和工业化地区。这项研究将增进对这种差异化板内火山系统的行为和危害的理解。 PI Schmitt 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研究人员的主要接待者。这些访问科学家和研究生将直接从与该项目相关的方法论进步中受益。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就读的体验。