Collaborative Research: Volatile Contents of Komatiites

智力上的优点。科马提岩对地球的热和成分演化提供了关键但有争议的限制。最重要的是科马提岩岩浆的含水率--在低含水率时，科马提岩的形成需要地幔潜在温度比现代值高500摄氏度，而湿熔融需要更温和的增加。目前对科马提石水分含量的估计是可变的，并引起了激烈的争论。此外，对科马提岩岩浆中其他挥发性元素(S、氟、氯)的丰度及其地幔来源知之甚少，尽管这些元素有可能为地球化学循环和脱气模型提供主要约束。我们建议对科马提岩中的挥发性成分进行合作研究。这将主要是通过测量保存完好的津巴布韦贝灵圭绿岩带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一些中低变质等级地体的科马提岩的检查和初步测量。这项研究将结合岩相学观察和微观分析技术：二次离子质谱仪(SIMS)、激光烧蚀电感耦合等离子体质谱(LA-ICPMS)和电子微探针分析(EMPA)。之前报道的贝灵圭样品熔体包裹体的数据不能确定科马提石的水分含量，我们提出了一个仔细的分析方案来纠正这一点。我们还将测定其他挥发性物种(二氧化碳、氟、S、氯)的丰度以及常量和微量元素、S和氢的形态和氢同位素组成。这些补充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组成及其地幔来源提供新的见解。初步数据表明，在我们手头的样品中，熔体包裹体中含有大量的和可测量的H2O、CO2、S和氯。总体而言，我们的研究将对科马提岩岩浆和太古代地幔和科马提岩源区的挥发分含量提供一些首次直接制约。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国际和平研究所，促进俄勒冈州立大学和华盛顿卡内基研究所这两个研究机构之间的合作，并为这两个地方的地球化学分析设施的开发和维护做出贡献。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，并吸引有才华的本科生参与最先进的研究和使用OSU和CIW的研究设施。来自俄亥俄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，这将包括访问CIW和实地考察加拿大Abitibi Greenstone带的科马提岩和伴生岩石的露头。这两位PI都积极促进本科生的研究。皮肯特正在为俄亥俄州立大学岩石学小组协调本科生研究，并将在2006年秋季共同教授一门面向大三和大四学生的本科生研究课程。俄勒冈州立大学的本科生研究目前正通过这些活动和最近聘用的本科生研究协调员重新焕发活力。

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.