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首页> 外文期刊>Journal of Asian earth sciences >Shallow submarine volcano group in the early stage of island arc development: Geology and petrology of small islands south off Hahajima main island, the Ogasawara Islands
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Shallow submarine volcano group in the early stage of island arc development: Geology and petrology of small islands south off Hahajima main island, the Ogasawara Islands

机译：岛弧发展初期的浅层海底火山群：小gas原群岛Hahajima主岛以南的小岛屿的地质和岩石学

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摘要

Small Islands south off Hahajima, the southernmost of the Ogasawara Archipelago, consist of primitive basalts (<12 wt.% MgO) to dacite erupted during the transitional stage immediately following boninite volcanism on the incipient arc to sustained typical oceanic arc. Strombolian to Hawaiian fissure eruptions occurring on independent volcanic centers for the individual islands under a shallow sea produced mag-nesian basalt to dacite fall-out tephras, hyaloclastite and a small volume of pillow lava, which were intruded by NE-trending dikes. These volcanic strata are correlated to the upper part (<40 Ma) of the Hahajima main island. Volcanic rock samples have slightly lower FeO'/MgO ratios than the present volcanic front lavas, and are divided into three types with high, medium and low La/Yb ratios. Basalt to dacite of high- and medium-La/Yb types show both tholeiitic (TH) and calc-alkaline (CA) differentiation trends. Low-la/Yb type belongs only to TH basalt. The multiple magma types are coexistence on the each island. TH basalts have phenocrysts of olivine, clinopyroxene and plagioclase, while CA basalts are free from plagioclase phenocrysts.
机译：小gas原群岛最南端的Hahajima南部的小岛由原始玄武岩（<12 wt。％MgO）组成，在过渡阶段的原始贝尼石火山作用之后的过渡阶段，镁铝石突然转变成持续的典型海洋弧。在浅海之下，各个岛屿的独立火山中心发生的斯特伦伯纪至夏威夷裂隙喷发产生了镁质玄武岩，形成了脱落的特弗拉斯，透明质岩和少量枕状熔岩，这些岩浆被NE趋势大堤侵入。这些火山岩地层与Hahajima主岛的上部（<40 Ma）相关。火山岩样品的FeO'/ MgO比值比目前的火山前熔岩稍低，并且分为高，中和低La / Yb比值的三种类型。高和中La / Yb类型的玄武岩至钠长晶岩显示出高生质（TH）和钙碱性（CA）的分化趋势。低la / Yb类型仅属于TH玄武岩。多个岩浆类型在每个岛上共存。 TH玄武岩具有橄榄石，斜辉石和斜长石的表晶，而CA玄武岩中没有斜长石的表晶。

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