Spin transition in magnesiowüstite and ultralow thermal conduction in ultralow velocity zones.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 41290576.
- Also identified by DOI 10.1038/s41467-025-65430-7 and PMC identifier 12647677.
- Licence recorded as CC BY-NC-ND.
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Abstract
Above Earth's core-mantle boundary (CMB), seismic studies revealed numerous enigmatic, small-sized patches of ultralow velocity zones (ULVZs) with anomalously lower velocities and higher density than ambient mantle. These regions may be enriched in Fe-rich oxides, and their thermal conductivity Ʌ would critically influence regional heat-flux and thermochemical evolution around CMB, but remains poorly constrained. Here we experimentally show that Ʌ of (Mg<sub>0.75</sub>,Fe<sub>0.25</sub>)O, Ʌ<sub>Fp25</sub>, and (Mg<sub>0.25</sub>,Fe<sub>0.75</sub>)O, Ʌ<sub>Fp75</sub>, both decrease across an iron spin-transition at 573 K, while such reduction is ~30-40% smaller than at room temperature, suggesting their Ʌ are less-affected across the spin-transition under deep-mantle's high temperatures. The temperature dependences of low-spin Ʌ<sub>Fp25</sub> and Ʌ<sub>Fp75</sub> (T <sup>-0.39</sup> and T <sup>-0.23</sup>, respectively) are weaker than the conventional T <sup>-0.5</sup> for high-spin state. If made of Fe-rich oxides (e.g., Fp75), ULVZs should have an ultralow thermal conductivity ( ~ 3.4 W m<sup>-1</sup> K<sup>-1</sup>). Such strong thermal insulation enhances local temperature, vitalizing regional mantle dynamics and thermochemical evolution, and growth of thermal plumes. The significant Ʌ discontinuity across CMB would induce heterogeneous amplitude and pattern of CMB heat-flux, potentially impacting geodynamo and geomagnetic stability.