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Geochemistry of abyssal peridotites from the super slow-spreading Southwest Indian Ridge near 65°E: Implications for magma source and seawater alteration

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The geochemical characteristics of abyssal peridotite samples from one dredge station (27°49.74′S, 65°02.14′E, water depth 4473 m) on the super slow-spreading Southwest Indian Ridge (SWIR) near 65°E were investigated. Abyssal peridotites recovered from this site were comprised mainly of lizardite, chlorite, carbonate and magnetite with minor amounts of talc, pyroxene phenocrysts and sparse olivines.

Serpentinites exhibit talc veins and major serpentine derived from serpentinization with relict olivine granuloblasts. Olivine grains in serpentinites display exsolution lamellae, indicating the occurrence of talc reduction or decompression during seawater–rock interaction. Pyroxene shows clear cleavage in two directions, with clinopyroxene or orthopyroxene exsolution lamellae. By contrast, bulk rock trace element patterns of serpentinites reveal depletion in most incompatible elements, similarly to the depleted mid-ocean ridge basalt mantle composition, indicating that the SWIR peridotites originated from a depleted mantle source magma and have experienced partial melting. Meanwhile, Rb, Ba, U, Pb, Sr, Li anomalies and the Ce/Pb ratio suggest that these serpentinites have been strongly altered by seawater.

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Acknowledgements

Authors would like to thank the crews of the DY105-17A cruise for the help to collect samples. The authors gratefully acknowledge Shanke Liu (IGGCAS), Dingshuai Xue (IGGCAS) and He Li (IGGCAS) for technical assistance with XRD and XRF analyses. We are most grateful for the detailed and constructive comments and suggestions provided by the anonymous reviewer and the Associate Editor Dr. Somnath Dasgupta, which significantly improved the content of this paper. They also like to thank International Science Editing for checking our English. This work was supported by National Natural Science Foundation of China (Grant No. 40830849, 40976027), Shandong Province Natural Science Foundation of China for Distinguished Young Scholars (Grant No. JQ200913), and National Special Fund for the Twelfth Five Year Plan of COMRA (Grant No. DY125-12-R-02 and Grant No. DY125-11-R-05).

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  1. Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China

    Zhigang Zeng, Qiaoyun Wang, Xiaomei Wang, Shuai Chen, Xuebo Yin & Zhaoxue Li

  2. Graduate University of Chinese Academy of Sciences, Beijing, 100049, China

    Xiaomei Wang & Shuai Chen

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  1. Zhigang Zeng
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Zeng, Z., Wang, Q., Wang, X. et al. Geochemistry of abyssal peridotites from the super slow-spreading Southwest Indian Ridge near 65°E: Implications for magma source and seawater alteration. J Earth Syst Sci 121, 1317–1336 (2012). https://doi.org/10.1007/s12040-012-0229-z

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