Calcium dissolution in bridgmanite in the Earth's deep mantle

Area of Science:

• Geophysics
• Mineral Physics
• Earth Science

Background:

• The lower mantle, comprising over half Earth's volume, requires accurate mineralogical understanding.
• Calcium silicate (CaSiO3) perovskite is considered the third most abundant mineral in the lower mantle.
• Bridgmanite and ferropericlase are the two most abundant lower mantle minerals.

Purpose of the Study:

• To investigate the solubility of calcium in bridgmanite at high pressures and temperatures.
• To determine the conditions under which CaSiO3 perovskite disappears in the lower mantle.
• To propose a new model for lower mantle mineralogical domains.

Main Methods:

• High-pressure and high-temperature experiments simulating lower mantle conditions.
• Analysis of calcium solubility in bridgmanite.
• Geophysical modeling of mineral phase transitions.

Main Results:

• Calcium solubility in bridgmanite significantly increases above 40 GPa and 2,300 K.
• CaSiO3 perovskite dissolves completely into bridgmanite at depths greater than 1,800 km along the geotherm.
• A transition from a two-perovskite domain (TPD) to a single-perovskite domain (SPD) of calcium-rich bridgmanite is proposed for the lower mantle.
• Iron plays a crucial role in enhancing calcium solubility in bridgmanite.

Conclusions:

• The lower mantle transitions from a TPD to an SPD with increasing depth.
• Temperature variations significantly impact the depth of the TPD-SPD transition.
• This finding necessitates revisions to deep-mantle mineralogy models and impacts our understanding of mantle composition, structure, dynamics, and evolution.