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Thin crust as evidence for depleted mantle supporting the Marion Rise



The global ridge system is dominated by oceanic rises reflecting large variations in axial depth associated with mantle hotspots. The little-studied Marion Rise is as large as the Icelandic Rise, considering both length and depth, but has an axial rift (rather than a high) nearly its entire length. Uniquely along the Southwest Indian Ridge systematic sampling allows direct examination of crustal architecture over its full length. Here we show that, unlike the Icelandic Rise, peridotites are extensively exposed high on the rise, revealing that the crust is generally thin, and often missing, over a rifted rise. Therefore the Marion Rise must be largely an isostatic response to ancient melting events that created low-density depleted mantle beneath the Southwest Indian Ridge rather than thickened crust or a large thermal anomaly. The origin of this depleted mantle is probably the mantle emplaced into the African asthenosphere during the Karoo and Madagascar flood basalt events.

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Figure 1: Physiographic and geoid maps of the SWIR with sample locations, and a map of the Icelandic rise for comparison.
Figure 2: Lithologic proportions by weight for SWIR dredges compiled from Supplementary Table 1 with proportions for the MAR Atlantis massif.
Figure 3: Bathymetric map of the 53° E ridge amagmatic segment with sample locations and contents.
Figure 4: Cartoon looking north from the Antarctic plate across the SWIR, showing the inferred crustal architecture along the Marion Rise.


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This work was supported by the Chinese National Key Basic Research Program (2012CB417300), China Ocean Mineral Resources Research and Development Association, and the US National Science Foundation (grant OCE-0526905). We thank the crew and scientists of RV Dayang Yihao Cruise 21. M. Sulanowska provided technical support. Z. Chen and Y. Liu analysed chrome spinels for us at the Guangzhou Institute of Geochemistry, Chinese Academy of Sciences. A glass sample from 53° E was analysed by F. Ji at the State Key Laboratory for Mineral Deposits Research, Nanjing University. We thank the Core and Rock Storage Facility of the Woods Hole Oceanographic Institution for curatorial support and access to samples. D. Sauter, R. Fisher and E. Bonatti provided additional unpublished sample descriptions and locations for the eastern and western SWIR. A review by Y. Niu encouraged us to provide more appropriate measurements of ridge depth and directed us to several important papers, greatly benefiting the manuscript and its conclusions.

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This article represents the first report of results of a survey during Cruise 21 Leg 5 of the RV Dayang Yihao directed by H.Z., who also had additional analytical work done at his institution. H.J.B.D. collected the bulk of the sample data over a period of 35 years. Both authors interpreted the results, with H.J.B.D. primarily responsible for the written text.

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Correspondence to Huaiyang Zhou or Henry J. B. Dick.

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Zhou, H., Dick, H. Thin crust as evidence for depleted mantle supporting the Marion Rise. Nature 494, 195–200 (2013).

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