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首页> 外文期刊>Contributions to Mineralogy and Petrology >Mantle dynamics and mantle melting beneath Niuafo'ou Island and the northern Lau back-arc basin
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Mantle dynamics and mantle melting beneath Niuafo'ou Island and the northern Lau back-arc basin

机译：Niuafo'ou岛和北部Lau后弧盆地下方的地幔动力学和地幔融化

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A suite of young volcanic basaltic lavas erupted on the intra-plate island of Niuafo'ou and at active rifts and spreading centres (the King's Triple Junction and the Northeastern Lau Spreading Centre) in the northern Lau Basin is used to examine the pattern of mantle flow and the dynamics of melting beneath this complex back-arc system. All lavas contain variable amounts of a subduction related component inherited from the Tonga subduction zone to the east. All lavas have higher ~(87)Sr/~(86)Sr, lower ~(143)Nd/~(144)Nd and more radiogenic Pb isotope compositions than basalts erupted at the Central Lau Spreading Centre in the central Lau Basin, and are interpreted as variable mixtures of subduction-modified, depleted upper mantle, and mantle residues derived from melting beneath the Samoan Islands which has leaked through a tear in the subducting Pacific Plate beneath the Vitiaz Lineament at the northern edge of the Lau Basin. Our data can be used to map out the present-day distribution of Samoan mantle in this region, and show that it influences the compositions of lavas erupted as far as 400 km from the Samoan Islands. The distribution of Samoan-influenced lavas implies south-and southwest-wards mantle flow rates of >4 cm/year. U-series disequilibria in historic Niuafo'ou lavas have average (~(230)Th/~(238)U) = 1.13, (~(231)Pa/~(235)U) = 2.17, (~(226)Ra/~(230)Th) = 2.11, and together with major and trace element data require approx 5 percent partial melting of mantle at between 2 and 3 GPa, with a residual porosity of 0.002 and an upwelling rate of 1 cm year~(-1). We suggest that intra-plate magmatism in the northern Lau Basin results from decompression melting during southward flow of mantle from beneath old (110-120 Ma), relatively thick Pacific oceanic lithosphere to beneath young (<5 Ma), thinner oceanic lithosphere beneath the northern Lau Basin.
机译：在劳阿盆地北部的板块内纽瓦弗岛以及活跃的裂谷和扩散中心（国王的三重交界处和东北劳扩散中心）爆发了一系列年轻的火山玄武岩熔岩。流和复杂的弧后系统融化动力学。所有熔岩都包含从东向汤加俯冲带继承的不同数量的俯冲相关成分。与在劳中盆地中央劳扩散中心喷出的玄武岩相比，所有熔岩具有更高的〜（87）Sr /〜（86）Sr，更低的〜（143）Nd /〜（144）Nd和更多的放射性Pb同位素组成。被解释为俯冲修饰的，贫化的上地幔和源自萨摩亚群岛下方融化的地幔残渣的可变混合物，萨摩亚群岛下方的熔融是通过劳流盆地北部边缘维蒂亚兹线下的俯冲太平洋板块的裂隙渗漏而来的。我们的数据可用于绘制该地区萨摩亚地幔的当前分布，并表明它影响了距萨摩亚群岛400公里处喷发的熔岩的成分。受萨摩亚影响的熔岩的分布意味着南，西南向地幔流速> 4厘米/年。在历史悠久的Niuafo'ou熔岩中的U系列失衡平均值为（〜（230）Th /〜（238）U）= 1.13，（〜（231）Pa /〜（235）U）= 2.17，（〜（226）Ra /〜（230）Th）= 2.11，再加上主要和微量元素数据，要求地幔在2至3 GPa之间部分熔化约5％，残余孔隙度为0.002，上升速率为1 cm年。 1）。我们认为，劳北盆地北部的板内岩浆作用是由于地幔从旧的（110-120 Ma），较厚的太平洋大洋岩石圈下方到年轻的（<5 Ma），较薄的海底岩石圈以下向南流动的减压融化的结果。劳盆地北部。

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