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）的学术价值：一些板内熔岩的高3 He/4 He签名的起源是当今地球科学中最有争议的话题之一。一般来说，签名的起源归结为两个相互竞争的模型：周球模型认为，高3 He/4 He熔岩起源于地幔的浅部，其中含有再循环的外星物质和/或经历过（U + Th）/3 He贫化过程，而羽流模型认为，高3 He/4 He熔岩起源于更原始的，下地幔中相对不含气体的部分。本研究试图通过检验哪一个模型能做出有效的预测来确定这两个模型中哪一个更好地解释了板内熔岩高3 He/4 He特征的起源。近球模型预测：（1）所有板内熔岩具有相似的成分特征，（2）某些板内熔岩具有高的3 He/4 He比值，而另一些板内熔岩具有低的3 He/4 He比值，（3）He与放射成因同位素之间没有相关性。羽流模型预测：（1）来自局部板内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）这些局部板内火山不具有高的3 He/4 He比值。 本研究利用东太平洋化石扩张中心和裂隙脊的镁铁质岩浆岩的He-Sr-Nd-Pb同位素组成及其相应的常量和微量元素化学特征对模型进行了检验，以验证模型是否得到数据的支持。更广泛的影响：该项目支持加州州的调查人员，并构成博士学位的一部分。一个学生的论文，他将负责大部分的化学和同位素分析以及分析结果的解释。所有分析都将支持利用斯克里普斯海洋学研究所现有的分析基础设施。该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研究的关键方面。该项目涉及与在线科学教育资源“地球指南”（http：//earthguide.ucsd.edu/）的创建者合作，制作一个互动式在线动画片，重点介绍构成大洋地壳的岩浆和熔岩的形成。 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，以及我们目前的理解所依据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.