Thermodynamic and Elastic Properties of Magnesite at Mantle Conditions: First-Principles Calculations

Magnesite (MgCO3) is a likely main host of carbonates in the mantle and plays an important role in the transport and storage of carbon in the Earth's mantle. Its physical properties at high pressure and high temperature (PT) are crucial for understanding the deep carbon cycle. Here we investigated thermodynamic and elastic properties of magnesite under the mantle PT conditions using first-principles calculations with local density approximation (LDA). Magnesite has the seismic velocities close to those of forsterite. The effect of the magnesite on seismic velocity of the carbonated peridotite and eclogite is subtle in the upper mantle. However, magnesite has much smaller seismic velocities and far larger elastic anisotropy than major minerals in the transition zone and lower mantle. The enrichment of magnesite in the transition zone and lower mantle will likely produce seismically detectable low-velocity zone and velocity anisotropy.