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Thallium Isotopic Compositions in Hawaiian Lavas: Evidence for Recycled Materials on the Kea Side of the Hawaiian Mantle Plume
Geochemistry, Geophysics, Geosystems ( IF 4.480 ) Pub Date : 2021-08-23 , DOI: 10.1029/2021gc009765
Nicole M. B. Williamson 1 , Dominique Weis 1 , Julie Prytulak 2
Affiliation  

Hawaiian volcanoes record 6 Ma of potentially deep mantle chemistry and form two parallel volcanic chains that are geochemically unique, named Loa and Kea. Loa volcanoes erupt lavas with isotopically enriched compositions thought to reflect the presence of recycled material in the deep mantle source of the Hawaiian plume. Variations in stable thallium (Tl) isotopes have been used to trace recycled pelagic ocean sediment from subduction to eruption in arc and intraplate lavas. Previous work attributed heavy Tl isotopic compositions in eight Loa samples to recycled sediments in their source. We reexamined this hypothesis using a large sample set (n = 34) of shield-stage, tholeiitic basalt from 13 Hawaiian volcanoes representing the entire range of isotopically enriched and depleted compositions along the Hawaiian chain. Samples were acid-leached prior to isotopic analysis to remove post-eruption alteration and resulting ε205Tl values show statistical differences between Loa and Kea volcanoes. Corresponding isotopic data and re-analyzed trace element concentrations suggest that the ε205Tl values are primary magmatic signatures. Possible co-variations between heavy ε205Tl and oxygen isotopes in samples from Kea-trend volcanoes could reflect the presence of ancient, recycled pelagic sediment on the Kea side of the Hawaiian plume, which samples the average deep Pacific mantle. As such, the deep mantle source of both Loa and Kea Hawaiian volcanoes may contain recycled materials of different natures and recycling histories, which supports work from both geophysical and geochemical studies suggesting that the Earth's lower mantle is chemically heterogeneous on multiple spatial scales.

中文翻译:

夏威夷熔岩中的铊同位素组成:夏威夷地幔柱 Kea 侧回收材料的证据

夏威夷火山记录了 6 Ma 的潜在深层地幔化学物质,并形成了两条地球化学上独特的平行火山链,分别命名为 Loa 和 Kea。罗阿火山喷发的熔岩中含有丰富的同位素成分,这被认为反映了夏威夷羽流的深部地幔源中存在回收材料。稳定铊 (Tl) 同位素的变化已被用于追踪从俯冲到弧形和板内熔岩喷发的再循环远洋沉积物。先前的工作将八个 Loa 样品中的重铊同位素组成归因于其来源中的再循环沉积物。我们使用大样本集(n = 34) 来自 13 座夏威夷火山的盾构阶段拉斑玄武岩,代表了沿夏威夷链的整个同位素富集和枯竭成分范围。在同位素分析之前对样品进行酸浸以去除喷发后的变化,由此产生的 ε 205 Tl 值显示了 Loa 和 Kea 火山之间的统计差异。相应的同位素数据和重新分析的微量元素浓度表明 ε 205 Tl 值是主要的岩浆特征。重 ε 205之间可能的协变来自 Kea 趋势火山的样本中的 Tl 和氧同位素可以反映夏威夷羽流的 Kea 一侧存在古老的、循环的远洋沉积物,夏威夷羽流对平均深太平洋地幔进行采样。因此,Loa 和 Kea Hawaii 火山的深地幔源可能包含不同性质和回收历史的回收材料,这支持地球物理和地球化学研究的工作,表明地球下地幔在多个空间尺度上具有化学异质性。
更新日期:2021-09-03
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