Diapir

A diapir (; from French diapir [djapiʁ], from Ancient Greek διαπειραίνω (diapeiraínō) 'to pierce through') is a type of intrusion in which a more mobile and ductilely deformable material is forced into brittle overlying rocks. Depending on the tectonic environment, diapirs can range from idealized mushroom-shaped Rayleigh–Taylor instability structures in regions with low tectonic stress such as in the Gulf of Mexico to narrow dikes of material that move along tectonically induced fractures in surrounding rock.

The term was introduced by Romanian geologist Ludovic Mrazek, who was the first to understand the principle of salt tectonics and plasticity. The term diapir may be applied to igneous intrusions, but it is more commonly applied to non-igneous, relatively cold materials, such as salt domes and mud diapirs. If a salt diapir reaches the surface, it can flow because salt becomes ductile with a small amount of moisture, forming a salt glacier.

Occurrence

Differential loading causes salt deposits covered by overburden (sediment) to rise upward toward the surface and pierce the overburden, forming diapirs (including salt domes), pillars, sheets, or other geological structures.

In addition to Earth-based observations, diapirism is thought to occur on Neptune's moon Triton, Jupiter's moon Europa, Saturn's moon Enceladus, and Uranus's moon Miranda.

Formation

Diapirs commonly intrude buoyantly upward along fractures or zones of structural weakness through denser overlying rocks. This process is known as diapirism. The resulting structures are also referred to as piercement structures.