Helium, Sr, Nd, and Pb Isotope Geochemistry of Intraplate Mafic Igneous Rocks in Eastern Pacific: Implications for the Origin of Linear Volcanic Chains

摘要卡斯蒂略(0550237)的智力价值：某些板内熔岩的高3He/4He特征的起源是当今地球科学中最有争议的话题之一。总的来说，这一特征的起源可以归结为两种相互竞争的模型：一种是行星模型，它认为高3He/4He熔岩来自地幔浅层，那里含有可回收的地外物质和/或经历了(U Th)/3He亏损过程；另一种是羽流模型，它声称高3He/4He熔岩来自下地幔更原始、相对未脱气的部分。本研究试图通过检验哪一种模型能够有效地预测板内熔岩的高3He/4He特征，来确定哪一种模型能更好地解释板内熔岩高3He/4He特征的成因。周球模型预测：(1)所有板内熔岩具有相似的成分特征；(2)一些板内熔岩具有高的3He/4He比值，而另一些则具有低的3He/4He比值；(3)He与放射性同位素特征之间没有相关性。羽流模型预测：(1)板内局部火山的熔岩具有不同于形成主要线性火山链的熔岩的氦源特征；(2)这些局部板内火山的3He/4He比值不高。这项研究利用东太平洋化石扩张中心和裂隙脊中镁铁质火成岩的氦-锶-钕-铅同位素组成，以及相应的常量元素和微量元素化学来检验模型，以确定数据支持哪些模型。更广泛的影响：这个项目支持加利福尼亚州的研究人员，并成为一名学生博士论文的一部分，该学生将负责大部分化学和同位素分析，并对分析结果进行解释。所有分析都将支持使用斯克里普斯海洋研究所现有的分析基础设施。这项研究还支持与加州海洋科学教育卓越中心(COSEE-CA)合作，与公众，特别是科学教育工作者和学生分享这项研究的关键方面。它涉及到与在线科学教育资源EarthGuide(http://earthguide.ucsd.edu/)，)的创建者合作，制作一个互动的在线动画特写，重点是组成洋壳的岩浆和熔岩的形成。此外，还包括板块构造的驱动力、地球隐藏内部的性质、行星流变学以及我们目前理解所基于的地球物理和岩石学证据。

ABSTRACT Castillo (0550237)Intellectual merit: The origin of the high 3He/4He signature of some intraplate lavas is one of the most controversial topics in Earth Science today. In general, the origin of the signature boils down to two competing models: the perisphere model, which states that high 3He/4He lavas originate from the shallow part of the mantle that contains recycled extraterrestrial materials and/or experienced (U + Th)/ 3He depletion processes, and the plume model, which claims that high 3He/4He lavas originate from a more primitive, relatively undegassed portion of the lower mantle. This research tries to determine which of the two models better explains the origin of high 3He/4He signature of intraplate lavas by testing which model makes valid predictions. The perisphere model predicts: (1) all intraplate lavas exhibit similar compositional characteristics, (2) some intraplate lavas have high whereas others have low 3He/4He ratios and (3) there is no correlation between He and radiogenic isotopic signatures. The plume model predicts: (1) lavas from localized intraplate volcanoes have a helium source signature different from those of lavas that form major linear volcanic chains and (2) these localized intraplate volcanoes do not have high 3He/4He ratios. This research uses He-Sr-Nd-Pb isotopic compositions of mafic igneous rocks from fossil spreading centers and fissure ridges in the eastern Pacific, as well as their corresponding major and trace element chemistry to test the models to see which is supported by the data. Broader Impacts: This project supports investigators in the state of California and form part of a Ph.D. dissertation of a student who will be responsible for much of the chemical and isotopic analyses and interpretation of the analytical results. All the analyses will support use of existing analytical infrastructure at the Scripps Institution of Oceanography. The research also supports work with the California Center for Ocean Sciences Education Excellence (COSEE-CA) to share key aspects of the research with the public, particularly science educators and students. It involves working with the creators of Earthguide (http://earthguide.ucsd.edu/), an online science educational resource to produce an interactive online animation feature focusing on the formation of magmas and lavas that comprise the oceanic crust. Also covered are the driving forces of plate tectonics, the nature of the Earths hidden interior, planetary rheology, and the geophysical and petrological evidence on which our current understanding is based.