Studies of the Evolution of the Terrestrial Mantle Using Neon Isotopes in Ocean Island and Island Arc Basalts

本研究以氖同位素为主要地球化学示踪剂，在两个相关的地幔研究领域进行地球化学研究。第一个领域涉及地幔柱的起源。不同种类的海洋岛玄武岩（OIB）之间的氖同位素非均质性将作为采样陆地地幔中不同储层的一种手段。该项目的最终目标是通过冰岛透明质碎屑岩和地下熔岩进一步评估He和Ne之间的关系，冰岛透明质碎屑岩和地下熔岩具有世界上最高的3He/4He值。计划对最原始地幔的氖同位素特征进行表征，并分析来自La Palma（西班牙）和Mangaia（库克群岛）的具有himu型地球化学特征的样品，以考虑这一重要地幔端元的Ne同位素特征。这部分研究的重点将是确定回收成分在OIB起源中的参与程度。该项目的第二个目标是考虑通过俯冲带进行挥发性回收的程度。此前由美国国家科学基金会（nsf）赞助的边际计划（MARGINS initiative）确定的两个俯冲带（中美洲和伊豆-博宁-马里亚纳系统）将成为研究目标，以寻找弧火山作用对挥发性产出的浅层和深层贡献的证据。氖同位素与其他地幔或空气源贡献指数（He和Ar的特定同位素）之间的关系将被研究，目的是量化它们对总质量平衡的贡献。稀有气体（和其他挥发物）的俯冲有可能对地幔的地球化学演化施加强有力的控制。该提案将对SIO/UCSD的两个研究活动领域产生影响。首先，它将重新建立一个专门的氖同位素设施，其主要作用是培养研究生和博士后访客。其次，氖气质谱仪（VG5400）位于SIO的流体和挥发物实验室。VG5400是该设施的重要补充，使学生和参观者都能接触到惰性气体研究的许多不同方面，增强他们的培训经验。

This study is to pursue geochemical studies in two related areas of terrestrial mantle research using neon isotopes as the primary geochemical tracer. The first area concerns the origin of mantle plumes. Neon isotopic heterogeneity among various classes of ocean island basalt (OIB) will be pursued as a means of sampling different reservoirs in the terrestrial mantle. The ultimate goal of the project is to further evaluate the relationship between He and Ne by targeting Icelandic hyaloclastites and sub-aerial lavas, which have amongst the highest 3He/4He values worldwide. The plan is to characterize the neon isotope characteristics of the most primitive mantle, and also, to analyze samples having HIMU-type geochemical characteristics from La Palma (Spain) and Mangaia (Cook Islands) to consider the Ne isotope characteristics of this important mantle end-member. The focus of this part of the study will be to ascertain the extent of involvement of recycled components in the genesis of OIB.A secondary goal of the project is to consider the extent of volatile recycling via subduction zones. Two subduction zones previously identified by the NSF-sponsored MARGINS initiative (Central America and the Izu-Bonin-Mariana system) will be targeted in order to search for evidence of shallow versus deep contributions to the volatile output via arc volcanism. Relationships between neon isotopes and other indices of mantle- or air-derived contributions (specific isotopes of He and Ar) will be investigated with the aim of quantifying their contributions to the total mass balance. Subduction of noble gases (and other volatiles) has the potential to exert a strong control on the geochemical evolution of the mantle.The impact of this proposal will be on two areas of research activity at SIO/UCSD. First, it will re-establish a dedicated neon isotope facility whose primary role is training of graduate students and post-doctoral visitors. Second, the neon mass spectrometer (VG5400) is sited in the Fluids and Volatiles Laboratory at SIO. The VG5400 is an important addition to the facility such that students and visitors alike will be exposed to many different facets of noble gas research enhancing their training experience.