Hydration at the base of the mantle transition zone by ancient subductions in Asia.

Ancient subduction in Asia is linked to present-day mantle hydration at the base of the mantle transition zone, with water reaching over 0.5 wt% beneath parts of the Mongol-Okhotsk suture zone.

• Why it matters: It remains unclear whether subduction enriches the mantle transition zone with water and how that history is preserved in today’s deep Earth structure.
• What they did: The study combined mineral-physics constraints on hydrous pyrolite with global seismic velocity structure and 660-km discontinuity topography to map water at the MTZ base.
• The result: An average global MTZ-base water content is about 0.14 wt%, while hydration anomalies tied to subduction reconstructions since 410 Ma reach above 0.5 wt% in the Mongol-Okhotsk suture zone, Central Asian Orogenic Belt, and Tethyan orogenic domain.

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