Links between the Archean hydrosphere and Earth's interior.

Area of Science:

• Geochemistry
• Early Earth Science
• Mantle Dynamics

Background:

• Earth's habitability relies on volatile cycling between the surface and mantle.
• The timing of this cycling and hydrosphere-mantle connection is debated.
• Komatiites, Archean ultramafic magmas, archive early mantle conditions.

Purpose of the Study:

• Investigate the initiation of volatile cycling into Earth's mantle.
• Determine the role of subduction in early Earth's volatile transport.
• Analyze potassium (K) isotope compositions in Archean komatiites.

Main Methods:

• High-precision K isotope analysis of komatiites from ten global localities.
• Interpreting isotopic signatures as indicators of mantle metasomatism.
• Correlating K isotope data with geological context of komatiite formation.

Main Results:

• Archean komatiites from three localities exhibit heavy K isotope compositions.
• These heavy isotope values exceed typical mantle and surface reservoir values.
• The heavy K signal suggests metasomatism by fluids from subducted oceanic lithosphere.

Conclusions:

• Surface-derived water was incorporated into mantle reservoirs by at least 3.6 billion years ago.
• Komatiites serve as crucial links between the Archean hydrosphere and Earth's interior.
• The study provides evidence for early subduction-style volatile recycling on Earth.