Unraveling Earth's Mysteries: From Viscosity Jump to Mountain Formation
An international research team has discovered that the sudden increase in viscosity in the Earth's lower mantle at depths of 800 to 1,200 km is due to the presence of bridgmanite-enriched rocks with larger grain sizes. These rocks, which make up a significant portion of the lower mantle, have a positive grain size dependence on viscosity. The viscosity jump affects various geophysical and geochemical processes, explaining phenomena such as the slowed sinking of subducted plates and the rapid upwelling of mantle plumes. The highly viscous bridgmanite-enriched rocks have been preserved in the deep lower mantle for billions of years.