start-ver=1.4 cd-journal=joma no-vol=53 cd-vols= no-issue=14 article-no= start-page=e2026GL122472 end-page= dt-received= dt-revised= dt-accepted= dt-pub-year=2026 dt-pub=20260728 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Electrical Conductivity of Hydrous Ultramafic Melts With Implications for Origin of Low Velocity Layer Atop of the 410 km Seismic Discontinuity en-subtitle= kn-subtitle= en-abstract= kn-abstract=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. en-copyright= kn-copyright= en-aut-name=YoshinoTakashi en-aut-sei=Yoshino en-aut-mei=Takashi kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=XieLongjian en-aut-sei=Xie en-aut-mei=Longjian kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 ORCID= affil-num=1 en-affil=Institute for Planetary Materials, Okayama University kn-affil= affil-num=2 en-affil=Center for High Pressure Science & Technology Advanced Research kn-affil= en-keyword=electrical conductivity kn-keyword=electrical conductivity en-keyword=water kn-keyword=water en-keyword=low velocity zone kn-keyword=low velocity zone en-keyword=silicate melt kn-keyword=silicate melt en-keyword=mantle kn-keyword=mantle END start-ver=1.4 cd-journal=joma no-vol=53 cd-vols= no-issue=14 article-no= start-page=e2026GL121981 end-page= dt-received= dt-revised= dt-accepted= dt-pub-year=2026 dt-pub=20260710 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Calcium Solubility of Bridgmanite in Subducted Basalt in Earth's Lower Mantle en-subtitle= kn-subtitle= en-abstract= kn-abstract=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. en-copyright= kn-copyright= en-aut-name=ZhangChengwei en-aut-sei=Zhang en-aut-mei=Chengwei kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=YoshinoTakashi en-aut-sei=Yoshino en-aut-mei=Takashi kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 ORCID= en-aut-name=El GhazaouiElias en-aut-sei=El Ghazaoui en-aut-mei=Elias kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=3 ORCID= en-aut-name=CharitonStella en-aut-sei=Chariton en-aut-mei=Stella kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=4 ORCID= en-aut-name=PrakapenkaVitali B. en-aut-sei=Prakapenka en-aut-mei=Vitali B. kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=5 ORCID= en-aut-name=LiLuo en-aut-sei=Li en-aut-mei=Luo kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=6 ORCID= en-aut-name=ZhangYanyao en-aut-sei=Zhang en-aut-mei=Yanyao kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=7 ORCID= en-aut-name=LinJung‐Fu en-aut-sei=Lin en-aut-mei=Jung‐Fu kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=8 ORCID= affil-num=1 en-affil=Department of Earth and Planetary Sciences, Jackson School of Geosciences The University of Texas at Austin kn-affil= affil-num=2 en-affil=Institute for Planetary Materials, Okayama University kn-affil= affil-num=3 en-affil=School of Earth and Environmental Sciences, Seoul National University kn-affil= affil-num=4 en-affil=Center for Advanced Radiation Sources, The University of Chicago kn-affil= affil-num=5 en-affil=Center for Advanced Radiation Sources, The University of Chicago kn-affil= affil-num=6 en-affil=Department of Earth and Planetary Sciences, Jackson School of Geosciences The University of Texas at Austin kn-affil= affil-num=7 en-affil=Earth and Planetary Sciences, Stanford University kn-affil= affil-num=8 en-affil=Department of Earth and Planetary Sciences, Jackson School of Geosciences The University of Texas at Austin kn-affil= END