Sluggish post-garnet transformation controls slab stagnation at the uppermost lower mantle

Area of Science:

• Geophysics
• Mineral Physics
• Earth Science

Background:

• Subducted slab behavior in the deep mantle is key to understanding Earth's evolution.
• Seismic data show slabs stagnate around 1000 km, but the cause is unclear.
• No known phase transitions at this depth explain the stagnation.

Purpose of the Study:

• Investigate the mechanisms behind deep mantle slab stagnation.
• Explain the enigmatic seismic observations of slab behavior.
• Propose a new model for slab stalling.

Main Methods:

• Simulated sluggish kinetics of the post-garnet transformation.
• Analyzed the resulting density deficit in subducting slabs.
• Modeled the duration of metastable garnet formation.

Main Results:

• Delayed post-garnet transformation kinetics create a density deficit.
• This deficit sustains metastable garnet, stalling slabs for millions of years.
• Slab stagnation is transient and linked to transformation kinetics.

Conclusions:

• Phase transformation kinetics offer a new explanation for slab stagnation.
• This model aligns with geophysical inferences of transient stagnation.
• Highlights the importance of kinetics in deep mantle dynamics.