Calcium carbonate (CaCO3) is a major host for CO2 in the deep Earth. The physical and chemical properties of CaCO3 at extreme pressure-temperature (P-T) conditions are indispensable to decipher the circulation of carbon between the Earth's interior and surface via volcanism and subduction. Using the pulse-echo-overlap method combined with Paris-Edinburgh press, we measured velocities of CaCO3 and observed an anomalous drop associated with the amorphization of aragonite under upper mantle conditions. The compressional (VP) and shear (VS) wave velocities of the partially amorphized CaCO3 are reduced by ~35% and 52% respectively, at 3.5–5.5 GPa and 1,073–1,373 K. The VP and VS of the partially amorphized CaCO3 are ~1/2 and 1/3 of what are expected for typical upper mantle minerals. The ultralow velocities of CaCO3 provide a possible alternative explanation for the slow seismic anomalies, such as the low-velocity layers atop the slabs, in the upper mantle.
CaCO3, low velocity zone
Hou, Mingqiang; Ming Hao; Jin Liu; Xiaowan Su; Wen-Yi Zhou; Rostislav Hrubiak; and Jin S. Zhang. "Ultralow velocities of CaCO3 and the origin of seismic anomalies in the Earth's upper mantle." (2021). https://digitalrepository.unm.edu/eps_fsp/12