Isotope fractionation in silicate melts by thermal diffusion.

Area of Science:

• Geochemistry
• Materials Science
• Physical Chemistry

Background:

• Thermal diffusion, or the Ludwig-Soret effect, describes mass transport driven by temperature gradients.
• Characterizing the Soret coefficient, S(T), is difficult due to its high sensitivity to various factors.
• Existing models struggle to robustly describe thermal diffusion across diverse compositions and temperatures.

Purpose of the Study:

• To develop a simplified and robust framework for characterizing thermal diffusion.
• To investigate the behavior of isotopic Soret coefficients in silicate melts.
• To explore the applicability of local thermodynamic equilibrium theory to thermal diffusion.

Main Methods:

• Experimental analysis of thermal diffusion across a wide range of compositions and temperatures.
• Focus on isotopic differences of network-modifying elements (Fe, Ca, Mg).
• Development of an additive decomposition model for the Soret coefficient.

Main Results:

• The difference in S(T) between isotopes of network modifiers is invariant with composition and temperature.
• This invariance allows for a predictable additive decomposition of S(T).
• Demonstrated a promising theoretical approach based on local thermodynamic equilibrium.

Conclusions:

• A simple and robust framework for characterizing isotope fractionation via thermal diffusion has been established.
• The findings are applicable to both natural and synthetic systems.
• Local thermodynamic equilibrium offers a viable theoretical basis for understanding thermal diffusion in complex solutions.