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

夏威夷链是热点火山活动的一个重要例子。岩浆岩的化学和同位素组成具有很大的差异，其组成的多样性反映了地幔中不同的源区成分以及地幔热柱与岩石圈和上地幔的相互作用。本项目引入锂同位素作为一种新的同位素示踪剂，用于研究洋岛玄武岩。近年来，随着质谱学技术的发展，海相储集层的锂同位素组成得到了精确的表征。海水、淡水和蚀变洋壳、海洋沉积物和地幔橄榄岩的锂同位素数据可用于评价夏威夷熔岩的来源。这项拟议的研究将集中于四座火山的熔岩：库劳火山、莫纳克亚火山、莫纳罗亚火山和基拉韦厄火山。库劳和莫纳克亚被认为是夏威夷火山的极端成分端元。同位素证据表明，库劳熔岩代表富含再循环洋壳和沉积物的羽流物质，而莫纳克亚熔岩则包含了再循环热液蚀变的下地壳熔体。锂同位素研究的目的是确定夏威夷羽流中的来源物质，包括从俯冲的大洋岩石圈和沉积物中回收的组分，并利用钻芯样品追踪岩浆的同位素随时间的演变。在更广泛的意义上，这项研究解决了地幔中的同位素不均质性、熔体-岩石圈相互作用和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.