91 / 2023-04-13 14:06:07

Prediction of potassium silicate hosts in Earth's deep mantle

potassium silicate,structure prediction,deep Earth

高压物理与材料科学 > 高压地球科学-II

Potassium isotope ⁴⁰K is considered one of the major sources of radiogenic heat in Earth’s interior but is also considered depleted in the mantle. Recently, K was detected in high concentrations in lower mantle minerals, indicating that K-rich regions might exist as hidden reservoirs in Earth's lower mantle. However, it is unclear how K can be hosted in minerals at high pressure, and how these are delivered to the deep mantle. Here, using first-principles calculations and structure predictions, stable K-silicate structures in the K₂O-SiO₂ binary system have been thoroughly investigated up to 130 GPa pressure. Results show that six K-silicate compounds are stable at lower mantle pressures, and these may act as K host minerals in deep Earth. We find four compositions stable in the D'' region, which may influence chemical exchange at the core-mantle boundary. Density profiles indicate that K can be concentrated in these silicates during subduction and be easily incorporated into upwelling mantle plumes due to buoyancy. Our results support the existence of large reservoirs of K in deep Earth and provide insights into the cycling processes for K in the mantle.