[S-IT17] Mass and energy transport in the crust and mantle: from properties to processes

[SIT17-05] Low fraction of volatile-charged carbonate melts in the upper mantle

*Yongsheng HUANG¹, Guoji Wu^1,2, Xuran Liang³, Kaiwei Tao^1,2, Michihiko Nakamura⁴, Yuan Li⁵ (1.State Key Laboratory of Deep Earth Processes and Resources, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China , 2.College of Earth and Planetary Sciences, University of the Chinese Academy of Sciences, Beijing 100049, China, 3.Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China, 4.Department of Earth Science, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan , 5.Bayerisches Geoinstitut, University of Bayreuth, 95440 Bayreuth, Germany)

Keywords:upper mantle, carbonate-charged melt, dihedral angle, complete wetting, carbonate melt volume, high electrical conductivity and low velocity anomalies

Carbonate melts serve as an ideal medium for metasomatism, facilitating the global material cycle between Earth's surface and its interior. Recently, high electrical conductivity and low seismic wave velocity anomalies have been detected at the bottom of upper mantle, which are attributed to the presence of carbonate-rich melt. However, the spatial distribution of carbonate-rich melt in the mantle rock remains elusive. Here, we experimentally investigate the effects of volatiles (H₂O and NaCl) and Al₂O₃-SiO₂ on the dihedral angle in olivine-carbonate melt systems under upper mantle conditions. Our findings reveal that the addition of volatiles significantly reduces the dihedral angle, reaching nearly 0° even at 1 GPa and 1200°C. Our results indicate that, at the bottom of the upper mantle, volatiles-bearing carbonate melt can completely wet the olivine grain boundaries. The decrease in dihedral angle is probably attributable to the high solubility of olivine in a low-viscosity carbonate melt containing volatiles. Our model calculations show that a minimal volume fraction of volatiles-bearing carbonate melt, ranging from 0.0002 to 0.06 vol%, sufficiently explains the observed high electrical conductivity and low velocity anomalies. The interconnected networks/films of volatile-charged carbonate melts effectively facilitate the permeation of melt, ultimately resulting in extensive metasomatism and matter transport within the upper mantle.