Upper mantle low-velocity layer tied to volatile-charged carbonate melts

Recent geophysical observations indicate the presence of small-volume, carbonate-rich melts in Earth's deep interior. However, the mechanisms by which such minute melt fractions migrate through largely solid rocks and generate large-scale geophysical anomalies have remained unclear. Here, our high-pressure experiments demonstrate that, in the presence of H₂O and NaCl, carbonate-rich melts act as super-spreaders, completely wetting and coating the surfaces of surrounding mantle minerals. This perfect wetting enables even trace amounts of melt (0.02 to 0.08 vol%) to form fully interconnected networks. Such connectivity facilitates efficient melt migration and chemical exchange, driving global material recycling between the surface and planetary interior.