Presentation Information
[SGC46-02]Pressure-stabilised Pb–S phases as deep-mantle hosts for unradiogenic lead: solving the lead isotope paradox?
*Simon A T Redfern1, Siyu Liu1, Shidong Yu1, Meng Guo2 (1.Nanyang Technological University, 2.Hong Kong University)
Keywords:
Lead isotope paradox,Lower mantle geochemistry,High-pressure sulfides,First principles calculations,Mantle differentiation
The distribution and cycling of lead (Pb) in Earth’s deep interior has long challenged geochemists due to the so-called “lead isotope paradox,” whereby mantle Pb isotopic compositions suggest reservoirs that have remained isolated since early differentiation. In this talk, I will present high-pressure first-principles predictions of novel Pb–S mineral phases that fundamentally alter our understanding of Pb partitioning in the lower mantle.
Using crystal structure prediction and density functional theory, we systematically explored the Pb–S binary system under pressures equivalent to the mantle’s mid to lowermost regions. We identify stable PbS2 and PbS3 polymorphs that are thermodynamically favoured at pressures above 70 GPa, with distinct electronic structures and robust polysulfide bonding motifs. These phases remain solid under conditions where PbS would melt, suggesting the possibility of pressure-stabilised solid Pb carriers in the deep mantle. Ab initio molecular dynamics and phonon analyses further constrain their stability fields and transport properties, revealing that they can incorporate unradiogenic Pb and resist remelting during mantle evolution.
By integrating mineral physics with mantle geochemistry, our results offer a quantitative mechanism for ancient Pb sequestration, with implications for long-lived heterogeneities in Earth’s interior and for models of core-mantle differentiation. The existence of such phases expands the suite of viable deep Pb hosts and provides a bridge between solid-state geochemistry and dynamical models of mantle reservoirs.
Using crystal structure prediction and density functional theory, we systematically explored the Pb–S binary system under pressures equivalent to the mantle’s mid to lowermost regions. We identify stable PbS2 and PbS3 polymorphs that are thermodynamically favoured at pressures above 70 GPa, with distinct electronic structures and robust polysulfide bonding motifs. These phases remain solid under conditions where PbS would melt, suggesting the possibility of pressure-stabilised solid Pb carriers in the deep mantle. Ab initio molecular dynamics and phonon analyses further constrain their stability fields and transport properties, revealing that they can incorporate unradiogenic Pb and resist remelting during mantle evolution.
By integrating mineral physics with mantle geochemistry, our results offer a quantitative mechanism for ancient Pb sequestration, with implications for long-lived heterogeneities in Earth’s interior and for models of core-mantle differentiation. The existence of such phases expands the suite of viable deep Pb hosts and provides a bridge between solid-state geochemistry and dynamical models of mantle reservoirs.