Collaborative Research: Chemical, Isotopic and Volatile Constraints on the Evolution of the Lau Basin

这项研究支持南加州两所大学的四名研究人员对西太平洋劳弧后盆地的岩浆过程进行全面的地球化学和同位素调查。该环境是研究和了解俯冲洋壳与其沉积物盖层、弧后地幔动力学、非均质性以及沿弧和海底喷发岩浆的地幔来源的理想场所。本工作旨在表征盆地下地幔的地球化学特征，并辨别其对盆地演化的控制作用。特别是，研究将集中在了解西太平洋劳盆地的海洋地壳组成如何受到太平洋板块向东俯冲的物质的影响。劳盆地一直是一个密集侦察工作的地点，目标地球化学样品套件包括400个熔岩和玻璃，这些样品是由斯克里普斯海洋研究所在nsf赞助的五次巡航中收集的。样品清单代表了劳盆地的广泛覆盖范围，包括来自所有公认扩散中心的熔岩。本研究将对具有代表性的火成岩和火山岩进行主微量元素化学分析（包括REE、HFSE和轻元素Li、Be、B、Cl）；挥发性元素（CO2, H2O）；Sr、Nd、Pb、Hf、He、Ne、Ar的同位素；以及U衰变系列的短寿命同位素（226Ra、230Th和234U）。利用这一前所未有的数据集，研究将能够解决以下四个问题：(1)是否有可能绘制出劳盆地印度型和太平洋型地幔的空间分布和范围；(2)劳盆地萨摩亚地幔柱成分的空间分布范围；(3)劳盆地扩张中心靠近Tofua弧对地幔熔融的影响；(4)劳盆地熔岩中挥发性富集的比例是由脊弧源相互作用引起的，还是由地壳同化等其他过程引起的。这项工作将为该区域的其他工作提供框架。这项工作对美国国家科学基金会资助的边际和RIDGE 2000项目的科学目标很重要。更广泛的影响：本研究的更广泛的影响包括对教育和培训至少三名研究生（博士和/或硕士）的贡献。此外，本科生将参与工作的选定方面。学生将在分析地球化学的一些分支学科中接受广泛的地球化学训练。此外，来自加州大学圣地亚哥分校（UCSD）的博士级学生在圣地亚哥州立大学（SDSU）的存在，没有博士课程，将刺激和挑战本科生和硕士生取得更高水平的成就。最后，该提案将有助于支持加州大学圣地亚哥分校和圣地亚哥州立大学的大量分析基础设施，并促进两所大学的教师和学生之间更密切的工作关系。

Intellectual MeritThis research supports four investigators at two southern California universities to carry out a comprehensive geochemical and isotopic investigation of magmatic processes occurring in the Lau back-arc basin in the western Pacific. The setting is an ideal one to study and understand links between subducting oceanic crust and its sediment cover, back-arc mantle dynamics, and heterogeneity as well as the mantle source of magmas erupting along the arc and on the seafloor. This work seeks to characterize the geochemistry of the mantle beneath the basin and discern its control on basin evolution. In particular, the research will focus on understanding how the composition of the ocean crust in the Lau Basin in the western Pacific Ocean is affected by materials coming from the Pacific plate that is being subducted to the east. The Lau Basin has been a site of intense reconnaissance work and the targeted geochemical sample suite consists of 400 lavas and glasses collected by Scripps Institution of Oceanography during five NSF-sponsored cruises to the region. The sample inventory represents extensive coverage of the Lau Basin, including lavas from all recognized spreading centers. This research will analyze representative igneous and volcanic rocks for major and trace element chemistry (including REE, HFSE, and light elements Li, Be, B, Cl); volatile elements (CO2, H2O); isotopes of Sr, Nd, Pb, Hf, He, Ne, and Ar; and short-lived isotopes of the U decay series (226Ra, 230Th, and 234U). With this unprecedented data set, the research will be able to address the following four issues: (1) whether it is possible to map the spatial distribution and extent of Indian- and Pacific-type mantles in the Lau Basin; (2) what the spatial extent of the Samoan mantle plume component in the Lau Basin is; (3) how the proximity of the Lau Basin spreading centers to the Tofua Arc affects mantle melting, and (4) what proportion of volatile enrichment in Lau Basin lavas is due to ridge-arc source interaction versus other processes such as crustal assimilation. This work will provide the framework for additional work in the region. The work is important for the science objectives of the NSF-funded MARGINS and RIDGE 2000 Programs. Broader Impacts: Broader impacts of this research include contributions to education and training of at least three graduate students (Ph. D. and/or M.S). Furthermore, undergraduates will be involved in selected aspects of the work. Students will receive broad geochemical training in a number of sub-disciplines of analytical geochemistry. In addition the presence of PhD-level students from the University of California, San Diego (UCSD) at San Diego State University (SDSU), which has no PhD program, will stimulate and challenge the undergraduate and Master's students to higher levels of achievement. Finally, the proposal will help to support the considerable analytical infrastructure at UCSD and SDSU, as well as foster closer working relationships between faculty and students at both institutions.