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Nat Commun. 2019 Jan 4;10(1):60. doi: 10.1038/s41467-018-07955-8.

Tiny droplets of ocean island basalts unveil Earth's deep chlorine cycle.

Author information

1
Department of Solid Earth Geochemistry, Japan Agency for Marine-Earth Science and Technology, Yokosuka, 237-0061, Japan. hanyut@jamstec.go.jp.
2
Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Nankoku, 783-8502, Japan.
3
Department of Solid Earth Geochemistry, Japan Agency for Marine-Earth Science and Technology, Yokosuka, 237-0061, Japan.
4
Earthquake Research Institute, The University of Tokyo, Bunkyo, Tokyo, 113-0032, Japan.
5
Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo, 152-8550, Japan.

Abstract

Fully characterising the exchange of volatile elements between the Earth's interior and surface layers has been a longstanding challenge. Volatiles scavenged from seawater by hydrothermally altered oceanic crust have been transferred to the upper mantle during subduction of the oceanic crust, but whether these volatiles are carried deeper into the lower mantle is poorly understood. Here we present evidence of the deep-mantle Cl cycle recorded in melt inclusions in olivine crystals in ocean island basalts sourced from the lower mantle. We show that Cl-rich melt inclusions are associated with radiogenic Pb isotopes, indicating ancient subducted oceanic crust in basalt sources, together with lithophile elements characteristic of melts from a carbonated source. These signatures collectively indicate that seawater-altered and carbonated oceanic crust conveyed surface Cl downward to the lower mantle, forming a Cl-rich reservoir that accounts for 13-26% or an even greater proportion of the total Cl in the mantle.

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