Backarc volcanism along the en echelon seamounts: The Enpo seamount chain in the northern Izu‐Ogasawara arc
Backarc volcanism along the en echelon seamounts: The Enpo seamount chain in the northern Izu‐Ogasawara arc
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DOI：
10.1029/2003gc000554
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发表时间：
2003-08
期刊：
影响因子：
3.7
通讯作者：
S. Machida;T. Ishii
中科院分区：
文献类型：
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作者：
S. Machida;T. Ishii
本文报道了恩坡海山链火山岩的详细岩石学分析结果，揭示了大洋岛弧背景下弧后雁梯队海山链的火山作用特征。根据原始玄武岩橄榄石斑晶中铬尖晶石的组成和大块岩石微量元素化学特征，确定了恩坡海山链中两种类型的火山岩套。“更富集组合体”（MES）具有丰富的HFSE成分（如Nb、Ta）、较高的Nb/Zr值和较低的Cr#。“低富集层”（LES）中HFSE成分减少，Nb/Zr值降低，尖晶石中Cr#含量高。这些结果需要不同的地幔源，对构成恩坡海山链的火山岩有不同的要求。矿物学和地球化学分析表明，LES熔岩内部的岩石学变化可以用分馏和开放体系岩浆混合来解释。相比之下，MES熔岩之间的变化需要不同的岩浆成因机制，因为该套内的岩石学变化不能用分选来解释。MES玄武岩也显示岩浆混合的矿物学证据。Enpo海山链上火山活动的特征是由亚碱性玄武岩、碱性安山岩和角闪岩（富水）安山岩组成的MES熔岩与由亚碱性玄武岩和分块安山岩组成的LES熔岩之间存在复杂的时空关系。我们认为这些特征是海洋岛弧弧后海山链岩浆系统变异性的特征。
We report results of detailed petrological analyses of volcanic rocks from the Enpo seamount chain that reveal the characteristics of volcanism in a backarc en echelon seamount chain in an oceanic island arc setting. We identified two types volcanic rock suites in the Enpo seamount chain based on bulk rock trace element chemistry and compositions of chrome spinels included in olivine phenocrysts of primitive basalts. “More Enriched Suites” (MES) have enriched HFSE compositions (such as Nb, Ta), higher Nb/Zr values, and low Cr# in spinel. “Less Enriched Suites” (LES) have depleted HFSE compositions, lower Nb/Zr values, and high Cr# in spinel. These results require distinct mantle sources with different for the volcanic rocks constituting the Enpo seamount chain. Mineralogical and geochemical analyses show that petrological variations within LES lavas are explained by fractionation with open system magma mixing. In contrast, variations between MES lavas require different mechanisms of magma genesis because petrological variation within this suite cannot be explained by fractionation. MES basalts also exhibit mineralogical evidence for magma mixing. Volcanism on the Enpo seamount chain is characterized by complex spatial and temporal relationships between MES lavas consisting of subalkaline basalt, alkaline andesite, and hornblende (water rich) andesite, and LES lavas consisting of subalkaline basalt and fractionated andesite. We suggest that these features are characteristic of variability within magma systems that feed backarc seamount chains in oceanic island arcs.