Origin of geochemically heterogeneous mid-ocean ridge basalts from the Macquarie Ridge Complex, SW Pacific
Origin of geochemically heterogeneous mid-ocean ridge basalts from the Macquarie Ridge Complex, SW Pacific
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DOI：
10.1016/j.lithos.2020.105893
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发表时间：
2020-11
期刊：
影响因子：
3.5
通讯作者：
Q. Jiang;R. Merle;F. Jourdan;H. Olierook;M. Chiaradia;K. Evans;Xuan‐Ce Wang;C. Conway;H. Bostock;R. Wysoczanski
中科院分区：
文献类型：
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作者：
Q. Jiang;R. Merle;F. Jourdan;H. Olierook;M. Chiaradia;K. Evans;Xuan‐Ce Wang;C. Conway;H. Bostock;R. Wysoczanski
麦夸里洋脊复合体位于新西兰以南的澳大利亚-太平洋板块边界，是一个崎岖的测深洋脊，由一系列海底海山和该复合体唯一的陆上部分麦夸里岛组成。麦夸里岛洋中脊玄武岩（MORB）表现出不同程度的不相容元素富集，其成分范围从典型的正常MORB到富集MORB。然而，这些玄武岩的同位素组成倾向于高μ类（μ = 238 U/204 Pb; HIMU）地幔成分，这对于MORB型岩石来说是不寻常的。这个地幔特征的起源尚不清楚，也不清楚这个同位素特征是整个MRC的特征还是麦夸里岛独有的。在这里，我们报告新的主要和微量元素丰度，和Sr，Nd和Pb同位素的样品从MRC海山和新的采样点麦夸里岛。地球化学和同位素数据表明，整个MRC包括正常的富集MORB。混合建模表明，MRC玄武岩的非均质同位素特征不是来自附近的Balleny地幔柱的污染，但与新生代Zealandia板内HIMU类玄武岩有密切关系。我们建议MRC玄武岩的非均质地球化学特征来自含角闪石的石榴辉石岩脉，这是由稀土元素部分熔融模型和Nd和Pb同位素比值与La/Sm之间的强相关性所支持的。我们认为辉石岩脉是在大洋岩石圈地幔中形成的，它是由来自拆离交代的Zealandia次大陆岩石圈地幔或来自软流圈俯冲物质的含水和碳酸盐质流体/熔体交代的。俯冲物质来源于古冈瓦纳古陆东缘沿着的古俯冲和/或现代俯冲作用。
The Macquarie Ridge Complex (MRC), located at the Australian–Pacific plate boundary south of New Zealand, is a rugged bathymetric ridge comprising a series of submarine seamounts and Macquarie Island, the only subaerial portion of the complex. Mid-ocean ridge basalts (MORBs) from Macquarie Island show various enrichments in incompatible elements with compositions ranging from typical normal MORB to enriched MORB. However, these basalts have isotopic compositions trending towards a high μ-like (μ =238U/204Pb; HIMU) mantle component, which is unusual for MORB-type rocks. The origin of this mantle signature is not understood, and it is unclear whether this isotopic signature is characteristic of the entire MRC or unique to Macquarie Island. Here we report new major and trace element abundances, and Sr, Nd, and Pb isotopes for samples from the MRC seamounts and from new sampling sites on Macquarie Island. The geochemical and isotopic data show that the entire MRC comprises normal to enriched MORB. Mixing modelling indicates that the heterogeneous isotopic signatures of the MRC basalts are not derived from contamination of the nearby Balleny mantle plume but have affinities with that of the Cenozoic Zealandia intraplate HIMU-like basalts. We propose that the heterogeneous geochemical signatures of the MRC basalts are derived from amphibole-bearing garnet pyroxenite veins, which is supported by the rare earth element partial melting modelling and strong correlations between Nd and Pb isotopic ratios vs La/Sm. We posit that the pyroxenite veins were generated in the oceanic lithospheric mantle, which was metasomatised by hydrous and carbonatitic fluids/melts derived either from delaminated, metasomatised Zealandia subcontinental lithosphere mantle, or from subducted material in the asthenosphere. The subducted material could be derived from ancient and/or recent subduction along the former east Gondwana margin.