Lithium Isotope Compositions of Hawaiian Lavas: A Study of Source Components

[903197] [qh]夏威夷火山链是热点火山作用的一个重要例子。盾状熔岩在化学和同位素组成上表现出相当大的变化。地幔成分的多样性反映了地幔源成分的差异性以及地幔柱与岩石圈和上地壳的相互作用。本项目引入锂同位素作为一种新的同位素示踪剂，用于海洋岛玄武岩的研究。质谱技术的最新发展使海相储层锂同位素组成的精确表征成为可能。海水、新鲜和蚀变海洋地壳、海洋沉积物和地幔橄榄岩的锂同位素数据可用于评估夏威夷熔岩的起源。拟议的研究将集中在四个火山的熔岩上：库劳火山、莫纳克亚火山、莫纳罗亚火山和基拉韦厄火山。库劳火山和莫纳克亚火山被认为是夏威夷火山的极端组成末端。同位素证据表明，库劳熔岩代表了富含循环海洋地壳和沉积物的羽流物质，而莫纳克亚火山熔岩则包含了循环热液蚀变的下地壳的熔体。锂同位素研究的目的是确定夏威夷地幔柱的源物质，包括从俯冲的海洋岩石圈和沉积物中回收的成分，并利用岩心样品随时间追踪岩浆的同位素演化。在更广泛的意义上，本研究解决了地幔同位素非均质性、熔体-岩石圈相互作用以及俯冲地壳物质的再循环等问题。

9903197ChanThe Hawaiian chain is an important example of hot spot volcanism. Shieldlavas exhibit considerable variation in chemical and isotopic composition.The compositional diversity reflects distinct source components in themantle and interaction of the mantle plume with lithosphere and the uppermantle. This project introduces lithium isotopes as a new isotopic tracerfor the study of ocean island basalts. Recent developments of massspectrometric techniques have led to precise characterization of lithiumisotope compositions of marine reservoirs. Lithium isotopic data ofseawater, fresh and altered ocean crust, marine sediments, and mantleperidotite are available to evaluate the origin of Hawaiian lavas. Theproposed study will focus on lavas from four volcanoes: Koolau, Mauna Kea,Mauna Loa and Kilauea. Koolau and Mauna Kea are considered to be extremecompositional endmembers in Hawaiian volcanoes. Isotopic evidence suggeststhat Koolau lavas represent plume material enriched with recycled oceaniccrust and sediments , whereas Mauna Kea lavas has incorporated melts ofrecycled hydrothermally altered lower crust. The objectives of the lithiumisotope study are to identify source material in the Hawaiian plume,including recycled components from the subducted oceanic lithosphere andsediments, and to trace the isotopic evolution of the magmas with timeusing drill core samples. In a broader sense, this study addresses theissues of isotopic heterogeneity in the mantle, melt-lithosphereinteraction, and recycling of subducted crustal material.