Isotope systematics of Li, Sr, Nd, and volatiles in Indian Ocean MORBs of the Rodrigues Triple Junction : Constraints on the origin of the DUPAL anomaly
Isotope systematics of Li, Sr, Nd, and volatiles in Indian Ocean MORBs of the Rodrigues Triple Junction : Constraints on the origin of the DUPAL anomaly
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DOI：
10.1016/j.gca.2006.10.004
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发表时间：
2007-02
影响因子：
5
通讯作者：
Y. Nishio;S. Nakai;T. Ishii;Y. Sano
中科院分区：
文献类型：
--
作者：
Y. Nishio;S. Nakai;T. Ishii;Y. Sano
DUPAL异常是在印度洋地幔中发现的一种放射性同位素异常，被解释为大尺度地幔不均匀性所致。为了提供新的限制DUPAL起源，我们分析了锂，锶，钕在新鲜的N-MORB玻璃回收罗德里格斯三重结在印度洋，从北大西洋的同位素比值。印度洋DUPAL N-MORB的Li同位素组成与北大西洋non-DUPAL N-MORB的Li同位素组成相当。印度洋MORB中DUPAL标志的源区与E-MORB型富集地幔源区具有明显不同的Li同位素组成。两个源区的143 Nd/144 Nd值均明显低于北大西洋N-MORB。除少数Koolau熔岩外，大多数具有类似低143 Nd/144 Nd特征的洋岛玄武岩的δ 7 Li值也高于北大西洋N-MORB。锂同位素的结果支持最近的建议，大量的回收下大陆地壳可能会产生印度洋DUPAL源的放射性同位素签名。
The DUPAL anomaly, a radiogenic isotope anomaly discovered in the Indian Ocean mantle, has been interpreted as due to a large-scale mantle heterogeneity. To provide new constraints on the DUPAL origin, we analyzed isotope ratios of Li, Sr, and Nd in fresh N-MORB glasses recovered from the Rodrigues Triple Junction in the Indian Ocean, and from the North Atlantic. The Li isotopic compositions of the Indian Ocean DUPAL N-MORBs were comparable to those of the North Atlantic non-DUPAL N-MORBs. The source of the DUPAL signature in Indian Ocean MORBs and the E-MORB-type enriched mantle source have quite different Li isotopic compositions. The143Nd/144Nd values of both sources are significantly lower than those of the North Atlantic N-MORBs. The δ7Li values of most oceanic island basalts with similar low143Nd/144Nd signatures are also higher than those of the North Atlantic N-MORBs, except for several Koolau lavas. The Li isotope results support the recent proposal that significant amounts of recycled lower continental crust might produce the radiogenic isotope signatures of the Indian Ocean DUPAL source.