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# Role of garnet shaping the 660-km seismic discontinuity

## Details

**Authors** Takayuki Ishii, Hiroshi Kojitani, Masaki Akaogi

**Year** 2026

**Publisher** Nature Communications

**Kind of work** article

**Discipline** Geology

**Applied** false

[Read it at the publisher](https://doi.org/10.1038/s41467-026-73717-6) 
10.1038/s41467-026-73717-6

## In authors' words

### What they set out to do (purpose)

To determine what mineral transformations actually produce Earth's 660-km seismic discontinuity, given that ringwoodite breakdown (the post-spinel transition) alone incompletely explains seismic observations.

### Who or what was studied (sample)

Synthetic mantle-analog mineral compositions (garnet-free and garnet-bearing) tested under laboratory conditions.

### How they did it (methods)

High-pressure, high-temperature experiments in a Kawai-type multi-anvil apparatus comparing garnet-free and garnet-bearing compositions under matched conditions.

### What they found (results)

The post-spinel transition does not occur independently but proceeds as a reaction coupled to a post-garnet transition, and this coupled mechanism explains the depth and variable structure of the 660-km discontinuity beneath both subduction zones and mantle plumes.

## Commentary

### In short

A major structural boundary inside a large system (Earth's mantle) arises from the coupled interaction of two distinct components rather than either acting alone, while the mantle as a whole retains a single, uniform composition rather than being a mixture of separate rock types.

**Patterns it shows** D, S, R

**Added** 2026-09-26

**How to cite this** Takayuki Ishii, Hiroshi Kojitani, Masaki Akaogi (2026). Role of garnet shaping the 660-km seismic discontinuity. Nature Communications.