Diapir

"If a diapir is outside an established plume it rises at a much slower rate," Loper says.

This final stage is characterized by the cooling and resolidification of the partially molten diapir within the mantle, slow subsidence at the surface, and greatly diminished rates of crustal addition.

Deeply buried deposits of sea-salt dome upwards and pass through the overlying strata, as a kind of intrusive lobe, eventually emerging at the surface – the rising tongue is called a diapir.