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Water-rich sublithospheric melt channel in the equatorial Atlantic Ocean

Nature Geoscience volume 11, pages 65–69 (2018)Cite this article

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Abstract

The lithosphere–asthenosphere boundary is the most extensive boundary on Earth, separating the mobile plate above from the convecting mantle below, but its nature remains a matter of debate. Using an ultra-deep seismic reflection technique, here we show a systematic seismic image of two deep reflectors that we interpret as the upper and lower limits of the lithosphere–asthenosphere boundary beneath a 40–70-million-year-old oceanic lithosphere in the Atlantic Ocean. These two reflections correspond to 1,260 °C and 1,355 °C isotherms and bound a low-velocity channel, suggesting that the lithosphere–asthenosphere boundary is thermally controlled. We observe a clear age dependency of this sublithospheric channel: its depth increases with age from 72 km where it is 40-Myr-old to 88 km where it is 70-Myr-old, whereas its thickness decreases with age from 18 km to 12 km. We suggest that partial melting, facilitated by water, is the main mechanism responsible for the low-velocity channel. The required water concentration for melting increases with age; nevertheless, its corresponding total mass remains relatively constant, suggesting that most of the volatiles in the oceanic sublithospheric channel originate from a horizontal flux near the ridge axis.

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Fig. 1: Study area of the seismic survey.
Fig. 2: Time-domain seismic image.
Fig. 3: The LAB image.
Fig. 4: The LAB as a function of age.

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Acknowledgements

The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007–2013)/ERC Advance Grant agreement no. 339442_TransAtlanticILAB. The discussions with C. Langmuir on petrology were extremely useful. This manuscript was substantially improved in response to the thoughtful suggestions of B. Romanowicz and C. Langmuir. T. Stern provided a very constructive review. This is an Intitut de Physique du Globe de Paris contribution number 3899.

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Authors and Affiliations

  1. Equipe de Géosciences Marines, Institut de Physique du Globe de Paris (CNRS, Paris Diderot, Sorbonne Paris Cité), Paris, France

    Fares Mehouachi & Satish C. Singh

  2. Earth Observatory of Singapore, Nanyang Technological University, Singapore, Singapore

    Satish C. Singh

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  1. Fares Mehouachi
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Contributions

S.C.S. designed the project, led the data acquisition, supervised F.M. and wrote the paper. F.M. processed the seismic data, carried out all the calculations, produced the figures and participated in the writing of the paper.

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Correspondence to Satish C. Singh.

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Mehouachi, F., Singh, S.C. Water-rich sublithospheric melt channel in the equatorial Atlantic Ocean. Nature Geosci 11, 65–69 (2018). https://doi.org/10.1038/s41561-017-0034-z

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