Sound velocity anomalies of limestone at high pressure and implications for the mantle wedge

ABSTRACT

Limestone mainly consisting of CaCO₃ is one of the most abundant carbonates on Earth's surface. The sound velocities of limestone at high pressure were determined at room temperature using ultrasonic interferometry in a multi-anvil apparatus. Softening and discontinuities in compressional (P) and shear (S) wave velocities have been observed at around 1.45 GPa due to the phase transition of CaCO₃-I to CaCO₃-II, and the coexistence of CaCO3-IIIb and CaCO3-III stay up to ∼5 GPa. Limestone under CaCO₃-I and CaCO₃-III phase has much lower velocities and higher V_P/V_S ratio than most crustal and mantle minerals and the PREM model. Phase transitions from CaCO₃-I to CaCO₃-II cause the abrupt reduction of V_P, V_S, and V_P/V_S. The low velocities and high/low V_P/V_S ratio are well consistent with the seismology observed in the mantle wedge. The result suggests that the subduction of limestone into Earth's interior would cause low-velocity anomalies in mantle wedges.

KEYWORDS:

• Limestone
• CaCO₃
• high pressure
• phase transition
• velocity

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Natural Science Foundation of China [grant number 42073063], the State key laboratory of earthquake dynamics [grant number LED2021B02], Open Foundation of the United Laboratory of High-Pressure Physics and Earthquake Science [grant number 2019HPPES08], [grant number 2022HPPES01], Key Laboratory of Earthquake prediction, Institute of Earthquake Forecasting, CEA [grant number 2017KLEP03].