Bulk-rock Major and Trace Element Compositions of Abyssal Peridotites: Implications for Mantle Melting, Melt Extraction and Post-melting Processes Beneath Mid-Ocean Ridges
Bulk-rock Major and Trace Element Compositions of Abyssal Peridotites: Implications for Mantle Melting, Melt Extraction and Post-melting Processes Beneath Mid-Ocean Ridges
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DOI：
10.1093/petrology/egh068
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发表时间：
2004-12
影响因子：
3.9
通讯作者：
Y. Niu
中科院分区：
文献类型：
--
作者：
Y. Niu
本文首次给出了太平洋和印度洋海脊转换系中�130深海橄榄岩样品的主量元素和微量元素数据。这些数据揭示了这些岩石的岩石成因、洋脊下的地幔熔融和熔体提取过程以及元素行为的重要特征。尽管深海橄榄岩是蛇纹岩，也经历了海底风化，但岩浆特征在块状岩石成分中仍然保存完好。氧化镁与逐渐变重的稀土元素(REE)的较好的负相关反映了不同数量的熔体贫化。这种熔体损耗可能是最近亚脊地幔熔融的结果，但也可能是来自富饶的地幔来源的先前熔体提取事件的遗传。块状岩石样品中的轻稀土元素(LREE)比同一样品组分的单斜辉石(Cpx)更富集，而不是更亏损。如果cpx LREE记录了亚脊地幔熔融过程，那么块状岩石LREE必然反映了熔融后的参考作用。轻稀土元素(如La、Ce、Pr、ND)与静止的高场强元素(如Nb、Zr)的显著相关性表明，轻稀土元素和高场强元素的富集化是共同的岩浆作用的结果。参考发生在山脊下的‘冷’热边界层(TBL)，上升的熔体通过该层迁移并与高级残渣相互作用。引用显然不影响对CPX遗迹进行微量元素分析。这一观察结果表明，晶界多孔熔体在热障涂层中迁移。上升的熔体可能在温度上不起反应，因此可能只影响了cpx边缘，这些边缘与沉淀的橄榄石、被困住的熔体和岩石的其余部分一起，随后被蛇纹岩化。观测到块状岩石的Zr/Hf和Nb/Ta比值变化很大，这是意想不到的。这两个比值之间的相关性与对玄武岩的观测结果是一致的，即DZr/DHF；1和DNb/DTA<；1。
This paper presents the first comprehensive major and trace element data for � 130 abyssal peridotite samples from the Pacific and Indian ocean ridge–transform systems. The data reveal important features about the petrogenesis of these rocks, mantle melting and melt extraction processes beneath ocean ridges, and elemental behaviours. Although abyssal peridotites are serpentinized, and have also experienced seafloor weathering, magmatic signatures remain well preserved in the bulk-rock compositions. The better inverse correlation of MgO with progressively heavier rare earth elements (REE) reflects varying amounts of melt depletion. This melt depletion may result from recent sub-ridge mantle melting, but could also be inherited from previous melt extraction events from the fertile mantle source. Light REE (LREE) in bulk-rock samples are more enriched, not more depleted, than in the constituent clinopyroxenes (cpx) of the same sample suites. If the cpx LREE record sub-ridge mantle melting processes, then the bulk-rock LREE must reflect post-melting refertilization. The significant correlations of LREE (e.g. La, Ce, Pr, Nd) with immobile high field strength elements (HFSE, e.g. Nb and Zr) suggest that enrichments of both LREE and HFSE resulted from a common magmatic process. The refertilization takes place in the ‘cold’ thermal boundary layer (TBL) beneath ridges through which the ascending melts migrate and interact with the advanced residues. The refertilization apparently did not affect the cpx relics analyzed for trace elements. This observation suggests grain-boundary porous melt migration in the TBL. The ascending melts may not be thermally ‘reactive’, and thus may have affected only cpx rims, which, together with precipitated olivine, entrapped melt, and the rest of the rock, were subsequently serpentinized. Very large variations in bulk-rock Zr/Hf and Nb/Ta ratios are observed, which are unexpected. The correlation between the two ratios is consistent with observations on basalts that DZr/DHf < 1 and DNb/DTa < 1. Given