Volcanic Sources of Volatile Platinum Group Elements

知识优势：尼加拉瓜火神马萨亚火山气溶胶的初步数据表明，铂族元素（PGE）浓度明显高于城市空气中的PGE浓度。城市空气通常被认为受到汽车催化转化器释放的PGE污染。这些气溶胶颗粒以Pt、Pd和Rh对城市地区造成区域性污染。据20世纪70年代中期以来格陵兰岛冰雪的记录，这些颗粒的远距离迁移被怀疑是环境中PGE浓度增加的原因。如果在马萨亚火山气溶胶中测量到的PGE浓度是典型的火山气溶胶，那么挥发性PGE排放在全球范围内具有重要意义，值得详细研究。Re-Os-Ir-Rh-Ru-Pt-Pd的岩浆分馏受相关含pge络合物（如氧化物、卤化氢、硫化物）的挥发性和岩浆的物理化学性质（温度、相关化学物质的流通量）的控制。尼加拉瓜火神马萨亚火山气溶胶的初步数据表明，与其他重要的PGE来源相比，PGE丰度模式具有强烈而独特的分馏性（即高Pd/Pt， Os/Ir, Ru/Rh）。这些独特的模式与1870 / 188o相结合，可以作为pge火山来源的独特指纹，只要它们是火山喷发的典型特征。如果pge丰度模式是地质记录中PGE来源的独特地球化学指标，那么它们可能具有潜在的应用范围，从鉴定有争议的冲击层到评估环境中PGE浓度的来源。我们建议通过分析来自三个监测良好的火山系统（夏威夷基拉韦厄火山的Pu'u O'o喷口）的气溶胶过滤器（气态和颗粒结合的PGE）来研究岩浆条件下Re， Os和互补PGE的挥发性；尼加拉瓜的火神马萨亚；埃特纳火山，意大利。这些遗址涵盖了广泛的火山系统，即典型的地幔-柱、板内和俯冲相关的火山，具有显著的二氧化硫通量。我们从Vulcan Masaya获得的初步数据似乎支持这样的假设，即挥发性PGE丰度模式，结合Os同位素分析，可以用来区分岩浆、人为和地外PGE来源。我们建议分析一组60-100个样品的Re/Os/PGE和Os同位素组成。将进行补充性的主要元素和微量元素分析，将Re/Os/PGE数据置于更广泛的地球化学背景下。更广泛的影响：除了促进对地外环境，海洋，地壳和地幔之间相互作用的基本理解外，本研究还将为WHOI的两名本科生暑期学生研究员提供研究和教育机会（REU）。该项目还将促进与英国和法国科学家的国际合作。Peucker-Ehrenbrinkand Sims将继续参与各种推广工作，与麻省理工学院/世卫组织联合项目的研究生和公众分享我们的科学成果。

Intellectual Merits:Preliminary data for volcanic aerosols from Vulcan Masaya, Nicaragua, indicate that platinum group element (PGE) concentrations are significantly higher than PGE concentrations in urban air. Urban air is generally considered contaminated with PGE released from automotive catalytic converters. Such aerosol particles regionally contaminate urban areas with Pt, Pd and Rh. Long range transport of such particles is the suspected cause of increasing PGE concentrations in the environment, as recorded in Greenland snow and ice since the mid 1970s. If PGE concentrations measured in volcanic aerosols from Vulcan Masaya are typical of volcanic aerosols in general, volatile PGE emissions are globally significant and merit detailed study. Magmatic fractionation of Re-Os-Ir-Rh-Ru-Pt-Pd is governed by the volatility of relevant PGE-containing complexes (e.g., oxides, hydrogen halides, sulfides) and the physicochemical properties of the magma (temperature, fugacities of relevant chemical species). Preliminary data for volcanic aerosols from Vulcan Masaya, Nicaragua, indicate that PGE abundance patterns are strongly and uniquely fractionated (i.e., high Pd/Pt, Os/Ir, Ru/Rh) compared to other important sources of PGE.These unique patterns, in conjunction with 187Os/188Os, may serve as a unique fingerprint forvolcanic sources of PGEs, provided they are typical for volcanic exhalations in general. If PGEabundance patterns are a unique geochemical indicator of PGE sources in the geologic record, they may have potential applications ranging from the identification of disputed impact layers to assessing origins of PGE concentrations in the environment.We propose to investigate volatility of Re, Os and complementary PGE at magmatic conditions by analyzing aerosol filters (gaseous and particle-bound PGE) from three well-monitored volcanic systems - Pu'u O'o vent of the Kilauea volcano, Hawaii; Vulcan Masaya, Nicaragua; Etna volcano, Italy. These sites encompass a wide spectrum of volcanic systems, i.e., archetypical mantle-plume, intraplate and subduction related volcanoes with significant SO2 fluxes. Our preliminary data from Vulcan Masaya seem to support the hypothesis that volatile PGE abundance patterns, in combination with Os isotope analyses, can be used to distinguish magmatic from anthropogenic and extraterrestrial PGE sources. We propose to analyze a suite of 60-100 samples for Re/Os/PGE and Os isotopic composition. Complementary major and trace element analyses will be carried out to place the Re/Os/PGE data in a broader geochemical context.Broader Impacts:In addition to advancing basic understanding of interaction between the extraterrestrialenvironment, the ocean, crust and mantle, this study will provide research and educationalopportunities (REU) for two undergraduate Summer Student Fellows at WHOI. The project willalso foster international collaborations with scientists in England and France. Peucker-Ehrenbrinkand Sims will continue to participate in a variety of outreach efforts to share our scientific resultswith graduate students in the MIT/WHOI Joint Program and the general public.