Collaborative Research: Volatile Contents of Komatiites

智力上的优点。科马提岩提供了关键的，但有争议的，对地球的热量和成分演化的限制。最重要的是科马提岩岩浆的含水量-在低含水量下，科马提岩的形成需要比现代值高500 C的地幔潜在温度，而湿熔融需要更适度的增加。目前对科马提岩含水量的估计是可变的，并存在激烈的争论。此外，相对知之甚少的其他挥发性元素（S，F，Cl）的丰度在科马提岩岩浆及其地幔来源，虽然这些有可能提供的地球化学循环和脱气模型的主要限制。我们建议在科马提岩挥发分含量的合作研究。这将主要是通过测量来自津巴布韦Belingwe绿岩带保存完好的科马提岩样品中硅酸盐和氧化物相中的熔融包裹体，但也将涉及对来自其他低和中等变质等级岩石的科马提岩的检查和初步测量。该研究将使用岩相观察和微量分析技术的组合：二次离子质谱法（西姆斯）;激光烧蚀电感耦合等离子体质谱法（LA-ICP-MS）和电子探针分析（EMPA）。以前的数据报告从熔体包裹体在贝林圭样品是不确定的科马提岩水含量的估计方面，我们提出了一个仔细的分析方案，以纠正这一点。我们还将测量其他挥发性物质（CO2，F，S，Cl）以及主要和微量元素，S和H形态和H同位素组成的丰度。这些额外的数据将有助于确定脱气，氢扩散，地壳同化，蚀变和其他可能改变原生水含量的过程的影响，但也将为科马提岩岩浆的成分及其地幔来源提供新的见解。初步数据表明，我们手头的样品中的熔体包裹体含有大量的H2O，CO2，S和Cl。总的来说，我们的研究将提供一些第一个直接限制的挥发分含量的科马提岩岩浆和太古代地幔和科马提岩源区。更广泛的影响。这项工作将解决几个更广泛的影响。这项工作将支持两个PI，促进两个研究机构之间的合作，俄勒冈州州立大学和华盛顿卡内基研究所，并有助于开发和维护地球化学分析设施在这两个地方。这项工作还将提供有关地球化学和热演化的基本信息，是研究地幔挥发性结构和演化的长期项目的一部分。这项工作的一个特别重要的影响将是促进本科生的研究，并在国家的最先进的研究和研究设施的使用在俄勒冈州立大学和CIW从事有才华的本科生。来自俄勒冈州立大学的两名本科生将进行与该项目有关的高级论文研究，这将涉及到CIW和加拿大Abitibi绿岩带的科马提岩和相关岩石的实地露头的访问。两个PI都积极促进本科生的研究。PI肯特正在协调俄勒冈州立大学岩石学小组的本科生研究，并将在2006年秋季为大三和大四学生共同教授本科生研究课程。在俄勒冈州的本科研究目前正在通过这些活动，并通过一个本科研究协调员最近就业重振。

Intellectual merit. Komatiites provide key, but controversial, constraints on the thermal and compositional evolution of the Earth. Of primary importance are the water contents of komatiite magmas - at low water contents formation of komatiites require mantle potential temperatures 500 C above modern values, whereas wet melting requires more modest increases. Present estimates of komatiite water contents are variable and hotly debated. Further, relatively little is known about the abundances of other volatile elements (S, F, Cl) in komatiite magmas and their mantle sources, although these have the potential to provide primary constraints for models of geochemical cycling and degassing. We propose a collaborative study of volatile contents in komatiites. This will primarily be through measurements of melt inclusions trapped within silicate and oxide phases in well-preserved komatiite samples from the Belingwe Greenstone Belt in Zimbabwe, but will also involve examination and preliminary measurements of komatiites from a selection of other low and medium metamorphic grade terranes. The study will use a combination of petrographic observations and microanalytical techniques: Secondary Ion Mass Spectrometry (SIMS); Laser Ablation Inductively-Coupled Plasma Mass Spectrometry (LA-ICP-MS) and Electron Microprobe Analysis (EMPA). Previous data reported from melt inclusions in Belingwe samples are not definitive in terms of estimates of komatiite water contents and we propose a careful analytical scheme to rectify this. We will also measure abundances of other volatile species (CO2, F, S, Cl) as well as major and trace elements, S and H speciation and H isotope composition. This additional data will help define the effects of degassing, hydrogen diffusion, crustal assimilation, alteration and other processes that have the potential to alter primary water contents, but will also provide new insights into the compositions of komatiite magmas and their mantle sources. Preliminary data demonstrate that melt inclusions in samples we have in hand contain significant and measurable abundances of H2O, CO2, S and Cl. Overall our study will provide some of the first direct constraints on the volatile contents of komatiite magmas and Archean mantle and komatiites source regions. Broader impacts. This work will address several broader impacts. The work will support two PI's, foster collaboration between two research institutions, Oregon State University and the Carnegie Institute of Washington, and contribute to development and maintenance of geochemical analysis facilities in both places. The work will also provide fundamental information about the chemical and thermal evolution of the earth and is part of a long-term project to investigate the volatile structure and evolution of the mantle. A particularly important impact of this work will be to foster undergraduate research and to engage talented undergraduates in state-of-the-art research and use of research facilities at OSU and CIW. Two undergraduates from OSU will perform senior thesis research related to the project and this will involve visits to both CIW and to field outcrops of komatiite and associated rocks in the Abitibi Greenstone Belt in Canada. Both PI's are active in fostering undergraduate research. PI-Kent is coordinating undergraduate research for the OSU petrology group and will co-teach a course in undergraduate research for juniors and seniors in Fall 2006. Undergraduate research at Oregon State is currently being reinvigorated through these activities and via recent employment of an undergraduate research coordinator.