Because that the basaltic oceanic crust with a lower density than the normal mantle has negative buoyancy near the 660-km discontinuity, so that it may be gravitationally trapped in this region.

We plot changes in the density of the subducted oceanic crust (mid-ocean-ridge basalt) with depth due to the post-garnet transformation in both equilibrium 21 and metastable models in Fig. 4.

Density is a significant difference, oceanic crust is made up of more dense rocks than continental crust, meaning oceanic crust sits lower in the mantle as compared to continental crust.

Fate of the subducted oceanic crust revealed by laboratory experiments Date: February 6, 2019 Source: Ehime University Summary: Laboratory experiments at extreme pressures and temperatures lead to ...

Fate of the subducted oceanic crust revealed by laboratory experiments. Ehime University. Journal Nature DOI 10.1038/s41586-018-0816-5 ...

A new study finds that rocky chunks of oceanic crust are stuck at the deepest layers of the mantle, ... That's because seismic waves travel differently through materials of various densities and ...

"We know that Earth's oceanic crust accounts for 60 percent of Earth's surface, and on average is four miles thick," said geomicrobiologist Mark Lever of Denmark's Aarhuis University, part of a ...

Plate tectonics has shaped the Earth's surface for billions of years: Continents and oceanic crust have pushed and pulled on each other, continually rearranging the planet's façade. As two ...