Metastable garnet in oceanic crust at the top of the lower mantle
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Summary
This summary is machine-generated.The post-garnet transformation in subducting oceanic crust is much slower than previously thought. This kinetic effect means the crust
Area Of Science
- Mineral Physics and Geodynamics
- High-pressure/high-temperature transformations in Earth's mantle
Background
- Oceanic tectonic plates subduct into the Earth's lower mantle.
- Garnet and silicate spinel decompose into silicate perovskite via post-garnet and post-spinel transformations, respectively.
- Previous phase equilibrium studies suggested post-garnet transformation occurs in the shallow lower mantle, implying subducted basaltic crust wouldn't become buoyant.
Purpose Of The Study
- To investigate the kinetics of the post-garnet transformation.
- To re-evaluate the buoyancy behavior of subducted basaltic crust entering the lower mantle considering transformation kinetics.
Main Methods
- In situ X-ray observations using sintered diamond anvils.
- Kinetic study of the post-garnet transformation under high-pressure/high-temperature conditions.
Main Results
- The kinetics of the post-garnet transformation are significantly slower than those of the post-spinel transformation.
- Metastable garnet can survive for approximately 10 million years even at 1,600 K.
- Metastable spinel breaks down rapidly at 1,000 K.
Conclusions
- The slow kinetics of the post-garnet transformation allow metastable garnet to persist for extended periods in the subducting slab.
- This persistence broadens the depth range at the top of the lower mantle where subducted oceanic crust can potentially become buoyant.
- Transformation kinetics are crucial for accurately modeling the fate and geodynamic implications of subducted oceanic crust.