The multiple depleted mantle components in the Hawaiian-Emperor chain
The multiple depleted mantle components in the Hawaiian-Emperor chain
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DOI：
10.1016/j.chemgeo.2019.119324
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发表时间：
2020-01-20
期刊：
影响因子：
3.9
通讯作者：
Garcia, Michael O.
中科院分区：
文献类型：
--
作者：
Harrison, Lauren N.;Weis, Dominique;Garcia, Michael O.
大洋岛屿玄武岩是地球化学研究的目标，因为它们提供了一个直接的窗口，地幔成分和丰富的信息与地球混合的动力学和时间尺度。以往的研究主要集中在大洋岛屿的盾状火山岩阶段，以及这些玄武岩中容易区分的更易熔、富集的地幔成分。地幔贫化组合物通常更难以分辨，除非大量的这种物质参与地幔熔融（例如，大洋中脊），或独特的过程允许它们的成分未经稀释地喷发，例如具有最少可熔富集成分的源的非常小程度的熔化（例如，再生玄武岩）或作为捕虏体（例如，深海橄榄岩）。地幔亏损组分，此处定义为具有低时间积分Rb/Sr的物质（低Sr-87/Sr-86）和高时间积分Sm/Nd和Lu/Hf比值（高Nd-143/Nd-144和Hf-176/Hf-177），来自潜在的超大体积储集层（高达地幔的80%），因此需要充分的表征，以估计地球和地幔衍生熔体的组成。本文以夏威夷-皇帝岛链为例，重点介绍洋岛玄武岩中的地幔亏损成分。夏威夷-皇帝链是类似于6000公里长的地质记录的深源夏威夷地幔柱，活动超过8100万年。夏威夷火山活动的演化经历了四个火山活动阶段：碱性前盾、拉斑玄武岩盾（占火山体积的80-90%）、碱性后盾（约1%）和硅不饱和再生（< 0.1%）。我们报告Pb-Sr-Nd-Hf同位素组成和微量元素浓度的三个振兴西北夏威夷海岭玄武岩和比较详尽的汇编数据集的玄武岩从夏威夷群岛的皇帝海山。西北夏威夷海脊（NWHR）包括51座火山，跨度约为4200万年。在夏威夷-皇帝链的弯曲和夏威夷群岛之间，没有高精度的同位素数据公布的再生阶段超过了类似的47%的链。NWHR和夏威夷岛再生玄武岩的地球化学相似，表明再生火山作用的一致来源超过1250万年。相比之下，来自最古老的皇帝海山的盾形阶段玄武岩的同位素组成更为贫乏（即，较高的Hf-176/Hf-177和Nd-143/Nd-144，具有较低的Sr-87/Sr-86和（208）Pb*/Pb-206*）和痕量元素浓度（即，高度不相容元素的浓度低得多）比所有其他比弯曲年轻的耗尽夏威夷玄武岩，包括NWHR再生玄武岩。最古老的皇帝海山（> 70 Ma）的强烈贫化源可能与晚白垩世在夏威夷地幔柱附近活动的库拉-太平洋-伊佐那木洋中脊扩张系统的相互作用有关。与此相反，不兼容的微量元素比例NWHR再生玄武岩需要一个独特的来源，在夏威夷地幔柱，是由古代（> 1 Ga）部分熔融，可能是古代回收的海洋岩石圈的印记。这一审查的地球化学的夏威夷贫化组件文件的需要，多个独特的贫化组合物的采样，每一个优先熔化在特定时期的夏威夷羽activity.This表明，组成的贫化组件可以演变的地幔柱的生命周期，在夏威夷地幔柱中的富集成分观察。亏损组分成分的变化主要受喷发时上地幔构造构型的控制（即，这种效应可能会影响到下地幔不同成分的采样所传递的信号。
Oceanic island basalts are targeted for geochemical study because they provide a direct window into mantle composition and a wealth of information on the dynamics and timescales associated with Earth mixing. Previous studies mainly focused on the shield volcanic stage of oceanic islands and the more fusible, enriched mantle components that are easily distinguished in those basalts. Mantle depleted compositions are typically more difficult to resolve unless large amounts of this material participated in mantle melting (e.g., mid-ocean ridges), or unique processes allow for their compositions to be erupted undiluted, such as very small degrees of melting of a source with minimal fusible enriched components (e.g., rejuvenated basalts) or as xenoliths (e.g., abyssal peridotites). Mantle depleted components, defined here as material with low time-integrated Rb/Sr (low Sr-87/Sr-86) and high time-integrated Sm/Nd and Lu/Hf ratios (high Nd-143/Nd-144 and Hf-176/Hf-177) relative to primitive mantle, derive from a potentially very large volume reservoir (up to 80% of the mantle), and therefore need adequate characterization in order estimate the composition of the Earth and mantle-derived melts. This review focuses on mantle depleted compositions in oceanic island basalts using the Hawaiian-Emperor chain as a case study. The Hawaiian-Emperor chain is the similar to 6000 km long geological record of the deeply sourced Hawaiian mantle plume, active for > 81 Myr. Hawaiian volcanism evolves through four volcanic stages as a volcano traverses the Hawaiian plume: alkalic preshield, tholeiitic shield (80-90% volcano volume), alkalic postshield (similar to 1%), and silica undersaturated rejuvenated (< 0.1%). We report Pb-Sr-Nd-Hf isotope compositions and trace element concentrations of three rejuvenated Northwest Hawaiian Ridge basalts and compare them to an exhaustive compiled dataset of basalts from the Hawaiian Islands to the Emperor Seamounts. The Northwest Hawaiian Ridge (NWHR) includes 51 volcanoes spanning similar to 42 m.y. between the bend in the Hawaiian-Emperor chain and the Hawaiian Islands where there is no high-precision isotopic data published on the rejuvenated-stage over similar to 47% of the chain. NWHR and Hawaiian Island rejuvenated basalts are geochemically similar, indicating a consistent source for rejuvenated volcanism over similar to 12.5 million years. In contrast, shield-stage basalts from the oldest Emperor Seamounts are more depleted in isotopic composition (i.e., higher Hf-176/Hf-177, and Nd-143/Nd-144 with lower Sr-87/Sr-86 and (208)pb*/Pb-206*) and trace element concentrations (i.e., much lower concentrations of highly incompatible elements) than all other depleted Hawaiian basalts younger than the bend, including NWHR rejuvenated basalts. The strongly depleted source for the oldest Emperor Seamounts (> 70 Ma) was likely related to interaction with the Kula-Pacific-Izanagi mid-ocean ridge spreading system active near the Hawaiian plume in the Late Cretaceous. In contrast, the incompatible trace element ratios of NWHR rejuvenated basalts require a distinct source in the Hawaiian mantle plume that was imprinted by ancient (> 1 Ga) partial melting, likely ancient recycled oceanic lithosphere. This review of the geochemistry of Hawaiian depleted components documents the need for the sampling of multiple distinctive depleted compositions, each preferentially melted during specific periods of Hawaiian plume activity.This suggests that the composition of depleted components can evolve during the lifetime of the mantle plume, as observed for enriched components in the Hawaiian mantle plume. Changes in the composition of depleted components are dominantly controlled by the upper mantle tectonic configurations at the time of eruption (i.e., proximity to a mid-ocean ridge), as this effect overwhelms the signal imparted by potentially sampling different lower mantle components through time.