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Water-rich sublithospheric melt channel in the equatorial Atlantic Ocean

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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https://hal-insu.archives-ouvertes.fr/insu-03589299
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Submitted on : Friday, February 25, 2022 - 3:16:49 PM
Last modification on : Sunday, February 27, 2022 - 3:08:31 AM

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Fares Mehouachi, Satish C. Singh. Water-rich sublithospheric melt channel in the equatorial Atlantic Ocean. Nature Geoscience, 2018, 11, pp.65-69. ⟨10.1038/s41561-017-0034-z⟩. ⟨insu-03589299⟩

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