Distinguishing melt and fluid subduction components in Umnak Volcanics, Aleutian Arc
Distinguishing melt and fluid subduction components in Umnak Volcanics, Aleutian Arc
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DOI：
10.1029/1999gc000010
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发表时间：
2000-06
期刊：
影响因子：
3.7
通讯作者：
C. Class;Daniel M. Miller;S. Goldstein;C. Langmuir
中科院分区：
文献类型：
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作者：
C. Class;Daniel M. Miller;S. Goldstein;C. Langmuir
会聚边缘的板块处理在主要地球储集层之间的元素分布中起着核心作用。然而，这种分布发生的机制仍然受到很少的限制。本文通过对阿留申弧中部乌姆纳克岛火山岩的详细同位素和微量元素研究，提供了新的约束条件。这些数据要求在弧下地幔中增加三个不同的俯冲成分，并对其进行了表征和量化：(1)来自俯冲洋壳的含水流体，具有类似大洋中脊玄武岩的同位素组成，但具有高的铅/钕比；(2)来自俯冲沉积物的含水流体，具有类似沉积物的同位素组成，并富含可流动元素；(3)沉积物部分熔融，具有类似沉积物的同位素组成，与区域和全球沉积物相比，具有较高的Th/Nd和Th/Nb。沉积物熔体中的流动元素是贫化的，表明熔融前流体的损失。沉积物熔体的高Th/Nb表明在部分熔融过程中存在金红石等富钛残留相。在不同的火山岩中可以区分出沉积流体和沉积物熔体，这表明它们分别到达了弧状岩浆形成的地点。这表明多个离散的流体和熔体相从沉积物释放到上覆地幔楔体，这可以被视为俯冲板递进变质的自然结果。
Plate processing at convergent margins plays a central role in the distribution of elements among major earth reservoirs. The mechanisms by which this distribution occurs, however, have remained poorly constrained. This paper provides new constraints through a detailed isotope and trace element study of volcanic rocks from Umnak Island, Central Aleutian Arc. The data require the addition of three distinct subduction components to the subarc mantle, which are characterized and quantified: (1) a hydrous fluid from subducted oceanic crust, with mid‐ocean ridge basalt (MORB)‐like isotopic compositions but high Pb/Nd; (2) a hydrous fluid from subducted sediment, with sediment‐like isotopic compositions and an enrichment in fluid‐mobile elements; (3) a sediment partial melt, with sediment‐like isotopic compositions and high Th/Nd and Th/Nb compared to both regional and global sediments. The sediment melt is depleted in fluid‐mobile elements, indicating loss of fluid prior to melting. The high Th/Nb of the sediment melt indicates presence of a Ti‐rich residual phase such as rutile during partial melting. The observation that sediment fluid and sediment melt can be distinguished in different volcanic rocks suggests that they arrive separately at the sites of arc magma formation. This indicates release of multiple discrete fluid and melt phases from sediment to the overlying mantle wedge, which can be viewed as a natural consequence of progressive metamorphism of the subducting slab.