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<\/p>\nThrough a collaborative research project under the joint usage project (PRIUS) at the Geodynamics Research Center (GRC), Ehime University, Assistant Professor ZHANG Youyue, together with Professor MAO Zhu and students from the University of Science and Technology of China (USTC), revealed the origin of the sporadic splitting of the 520-km mantle discontinuity. This splitting manifests as a secondary seismic reflector near 560 km beneath subduction zones and mantle upwellings. However, previous models based on normal davemaoite () exsolution could not produce the required 2\u20134% impedance contrast observed in seismic data.<\/p>\n
In this study, high pressure-temperature experiments (~20 GPa, 1,200\u20131,600 \u00b0C) simulating mantle transition zone conditions were performed using a composition similar to carbonate-altered oceanic crust. The findings demonstrate that carbonate addition drives Ca-Mg exchange with silicates, increases Ca incorporation into silicates under Fe-rich conditions, and significantly enhances davemaoite exsolution. This process concentrates davemaoite to 12\u201333 vol.% near a depth of ~560 km, generating a sufficient elastic contrast to match the seismic observations.<\/p>\n
This study demonstrates that deep carbon cycling driven by subducted carbonates reshapes mineral equilibria and generates persistent seismic signatures in the deep interior. It offers crucial insights into mantle material recycling and the physical and chemical evolution of Earth’s interior.<\/p>\n
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