American Geophysical Union (AGU) Acta Medica Okayama 0094-8276 53 14 2026 Electrical Conductivity of Hydrous Ultramafic Melts With Implications for Origin of Low Velocity Layer Atop of the 410 km Seismic Discontinuity e2026GL122472 EN Takashi Yoshino Institute for Planetary Materials, Okayama University Longjian Xie Center for High Pressure Science & Technology Advanced Research Low-velocity layers (LVLs) above the 410-km discontinuity are commonly attributed to partial melt generated by dehydration melting when hydrous mantle transition-zone material rises into the upper mantle, where water solubility in nominally anhydrous minerals decreases. Interpreting coexisting high-conductivity anomalies requires constraints on the intrinsic conductivity of the melt phase at pressures just above the transition zone. We measured electrical conductivity of hydrous ultramafic melts representative of incipient melts, ranging from 6.3 to 18.6 wt% H2O at 13 GPa using impedance spectroscopy in a Kawai-type multi-anvil apparatus. Hydrous ultramafic melts are extremely conductive, and conductivity increases systematically with H2O content to values comparable to alkali-carbonate melts. The high conductivity implies that even small fractions of interconnected hydrous melt can dominate bulk mantle conductivity. Combining our measurements with geophysical conductance estimates indicates that <1 vol% melt can produce conductive layers thicker than 10 km, consistent with seismological constraints on LVL structure. No potential conflict of interest relevant to this article was reported.

American Geophysical Union (AGU) Acta Medica Okayama 0094-8276 53 14 2026 Calcium Solubility of Bridgmanite in Subducted Basalt in Earth's Lower Mantle e2026GL121981 EN Chengwei Zhang Department of Earth and Planetary Sciences, Jackson School of Geosciences The University of Texas at Austin Takashi Yoshino Institute for Planetary Materials, Okayama University Elias El Ghazaoui School of Earth and Environmental Sciences, Seoul National University Stella Chariton Center for Advanced Radiation Sources, The University of Chicago Vitali B. Prakapenka Center for Advanced Radiation Sources, The University of Chicago Luo Li Department of Earth and Planetary Sciences, Jackson School of Geosciences The University of Texas at Austin Yanyao Zhang Earth and Planetary Sciences, Stanford University Jung‐Fu Lin Department of Earth and Planetary Sciences, Jackson School of Geosciences The University of Texas at Austin The calcium solubility in bridgmanite and the resulting abundance of davemaoite under lower-mantle pressure-temperature conditions have been under debate following a recent report of extensive calcium dissolution in bridgmanite. We experimentally investigated the calcium solubility in bridgmanite in a basaltic composition at pressures up to 125 GPa and temperatures up to 3,520 K. Our experimental data are modeled thermodynamically along the bridgmanite-davemaoite solvus to quantify the calcium solubility in bridgmanite and the davemaoite proportion in basaltic and pyrolitic assemblages along lower mantle geotherms. Our results indicate that bridgmanite hosts only 0.001–0.03 Ca cations per formula unit in the lower mantle, while davemaoite remains as an abundant mineral, accounting for 8 and 25 vol% of pyrolitic and basaltic mineralogical models, respectively, along representative lower-mantle geotherms. Our thermoelastic modeling further indicates that the effect of calcium dissolution on the density and bulk sound velocity of lower-mantle assemblages is negligible. No potential conflict of interest relevant to this article was reported.