Long-term core-mantle interaction explains W-He isotope heterogeneities

Area of Science:

• Geochemistry
• Isotope Geochemistry
• Planetary Science

Background:

• Ocean island basalts (OIBs) provide insights into Earth's mantle evolution.
• A puzzling anticorrelation exists between tungsten (W) and helium (He) isotopes in OIBs.
• Existing models struggle to explain this W-He isotopic anticorrelation without invoking complex or unobserved processes.

Purpose of the Study:

• To investigate the role of isotopic diffusion across the core-mantle boundary (CMB) in explaining OIB W-He isotopic anomalies.
• To challenge the necessity of deep, undegassed mantle reservoirs for explaining high ³He/⁴He signatures.
• To explore the implications of core-mantle exchange for early Earth conditions.

Main Methods:

• Numerical modeling of long-term isotopic evolution in mantle domains.
• Simulating isotopic diffusion of tungsten and helium across the CMB.
• Comparing model predictions with observed W-He isotopic heterogeneities in OIBs.

Main Results:

• Isotopic diffusion across the CMB can simultaneously transport W and He, naturally explaining the observed anticorrelation.
• The proposed diffusion mechanism adequately accounts for isotopic ratios in plume sources.
• The model obviates the need for a primordial, undegassed deep mantle reservoir.

Conclusions:

• Core-mantle boundary diffusion is a viable mechanism for generating OIB W-He isotopic signatures.
• This mechanism has significant implications for understanding mantle composition and early Earth differentiation.
• The findings challenge traditional models of mantle evolution and early Earth processes.