Electrical Conductivity of (Mg, Fe)CO3 at the Spin Crossover and Its Implication for Mid‐Mantle Geomagnetic Heterogeneities

• Published in: Geophysical research letters Vol. 51; no. 22
• Main Authors: Zhao, Chaoshuai, Liu, Jin, Xu, Liangxu, Hou, Mingqiang, Zhuang, Yukai, Zhu, Jie, Lin, Jung‐Fu
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.11.2024
• Subjects: (Mg, Fe)CO3; Anomalies; Bearing materials; Carbon; Depth; Diamonds; Electrical conductivity; Electrical resistivity; Geomagnetic anomalies; geomagnetic anomaly; Geomagnetic observations; Geomagnetism; high pressure; High temperature; High temperature effects; Iron carbonate; Iron content; Iron oxides; Lower mantle; Magnesium; Magnetic anomalies; Minerals; Mixtures; spin crossover; Temperature effects
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2024GL111046

(Mg, Fe)CO3 is an important deep carbon carrier and plays a vital role in our understanding of lower‐mantle carbon reservoirs. The electrical conductivity (EC) of FeCO3 was measured at 126−2000 K up to 83 GPa in diamond‐anvil cells using a standard four‐probe van der Pauw method. Moreover, the EC of FeCO3 increases by ∼6 orders of magnitude from 300 to 1500 K at 10−20 GPa, indicating a strong effect of high temperature. The EC of Fe0.65Mg0.35CO3 was measured up to 60 GPa at 300 K, the EC values of (Mg, Fe)CO3 are proportional to iron content and increase by 2–3 orders of magnitude at 300 K across the spin crossover. The EC values of (Mg, Fe)CO3 and FeCO3 + Fe3O4 ± C mixtures surpass that of bridgmanite, ferropericlase and davemaoite by ∼1–4 orders of magnitude at depths of 800–2,000 km. This result sheds insights into the genesis of local geomagnetic heterogeneities in the mid‐lower mantle. Plain Language Summary Geomagnetic observations reveal electrical heterogeneities in the mid‐lower mantle. However, some of the aforementioned geomagnetic anomalies are higher than the electrical conductivity (EC) values of major lower‐mantle minerals such as ferropericlase, bridgmanite, and davemaoite. This calls for the existence of high conductive mineral(s) in the region where subducting slabs can bring certain amounts of Fe‐bearing and/or carbon‐bearing materials. In this study, we report that EC values of (Mg, Fe)CO3 and FeCO3 + Fe3O4 ± C mixtures are 1–4 orders of magnitude greater than that of the major minerals at depths of 800–2,000 km. This suggests (Mg, Fe)CO3‐bearing and its decomposed mixtures subducting patches may induce local geomagnetic heterogeneities at these depths. In particular, these materials may contribute to the geomagnetic anomalies observed at ∼1,300 km depths and assist in identifying potential carbon‐rich regions in the lower mantle. Key Points Electrical conductivity (EC) of FeCO3 was measured at 126−2000 K and 0–83 GPa using the van der Pauw method in diamond‐anvil cells EC of (Mg, Fe)CO3 is proportional to iron content and increases by 2–3 orders of magnitude at the spin crossover High conductivity of (Mg, Fe)CO3 and FeCO3 + Fe3O4 ± C mixtures may contribute to local geomagnetic heterogeneities in the mid‐lower mantle