Extreme geochemical heterogeneity beneath the North Tonga Arc: Interaction of a subduction zone with intraplate seamount chains
Extreme geochemical heterogeneity beneath the North Tonga Arc: Interaction of a subduction zone with intraplate seamount chains
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DOI：
10.1016/j.chemgeo.2022.120903
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发表时间：
2022-05
期刊：
影响因子：
3.9
通讯作者：
B. Storch;M. Regelous;Kristina Noebel;K. Haase;J. Bauer
中科院分区：
文献类型：
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作者：
B. Storch;M. Regelous;Kristina Noebel;K. Haase;J. Bauer
我们提供了来自最北端大洋汤加岛弧的六个年轻海底火山的熔岩的新的地球化学和同位素数据。这些熔岩具有低浓度的中等不相容的微量元素，但与所有其他汤加岛弧熔岩相比，它们富含Nb和Ta，其Nd、Hf和Pb同位素组成与附近萨摩亚热区的复活熔岩相似。这些不寻常的成分表明，北汤加熔岩的地幔来源在之前的熔融事件中被耗尽，然后被部分熔体重新富集，该部分熔体富含与萨摩亚板内熔岩类似的高度不相容的元素。萨摩亚地幔在汤加北部岛弧和刘盆地下方向南流动，部分原因是汤加板块岩石圈的裂谷作用。后来，从俯冲的远洋沉积物和俯冲的路易斯维尔海山链火山物质的混合物中添加了一种流体成分。我们的新数据表明，路易斯维尔组分只在沿弧前100000公里的∼火山产生的熔岩中发现，这表明洋壳在俯冲过程中通过脱水在相对较小的深度区间内损失了铅。因此，汤加岛弧北部熔岩的成分受来自两个热点的物质的影响：过去6 Ma来自弧下活动的萨摩亚热柱的地幔向南流入，以及来自>；80 Ma古老的俯冲路易斯维尔海山链玄武岩的俯冲成分。
We provide new geochemical and isotope data for lavas from six young submarine volcanoes from the northernmost oceanic Tonga island arc. These lavas have low concentrations of moderately incompatible trace elements, but are enriched in Nb and Ta compared to all other Tonga island arc lavas, and their Nd, Hf and Pb isotope compositions resemble those of rejuvenated lavas from the nearby Samoa hotspot. These unusual compositions indicate that the mantle source of North Tonga lavas was depleted by prior melting events, before re-enrichment by a partial melt enriched in highly incompatible elements with Nd, Hf and Pb isotope compositions similar to Samoan intraplate lavas. Samoa plume mantle is flowing southwards beneath the northern Tonga island arc and Lau Basin, in part guided by rifting of the Tonga plate lithosphere. A fluid component was later added from a mixture of subducted pelagic sediment and subducting Louisville Seamount Chain volcanic material. Our new data show that the Louisville component is only found in lavas from volcanoes occurring along ∼100 km of the arc front, indicating that the oceanic crust loses Pb by dehydration over a relatively small depth interval during subduction. The compositions of lavas from the northern Tonga island arc are therefore influenced by material from two hotspots; southwards inflow of mantle from the active Samoa plume beneath the arc within the past 6 Ma, and a subduction component from >80 Ma old subducted Louisville Seamount Chain basalts.