Wiktionary
n. (context geology English) An intrusion of a ductile rock into an overburden.
WordNet
n. a domed rock formation where a core of rock has moved upward and pierced through the more brittle overlying strata
Wikipedia
A diapir (; French, from Greek diapeirein, to pierce through) is a type of geologic intrusion in which a more mobile and ductily deformable material is forced into brittle overlying rocks. Depending on the tectonic environment, diapirs can range from idealized mushroom-shaped Rayleigh–Taylor-instability-type 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 the Romanian geologist Ludovic Mrazek, who was the first to understand the principle of salt intrusion and plasticity. The term "diapir" may be applied to igneous structures, but it is more commonly applied to non-igneous, relatively cold materials, such as salt domes and mud diapirs.
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.
Diapirs commonly intrude vertically upward along fractures or zones of structural weakness through denser overlying rocks because of density contrast between a less dense, lower rock mass and overlying denser rocks. The density contrast manifests as a force of buoyancy. The process is known as diapirism. The resulting structures are also referred to as piercement structures.
In the process, segments of the existing strata can be disconnected and pushed upwards. While moving higher, they retain much of their original properties such as pressure, which can be significantly different from that of the shallower strata they get pushed into. Such overpressured Floaters pose a significant risk when trying to drill through them. There is an analogy to a Galilean thermometer.
Rock types such as evaporitic salt deposits, and gas charged muds are potential sources of diapirs. Diapirs also form in the earth's mantle when a sufficient mass of hot, less dense magma assembles. Diapirism in the mantle is thought to be associated with the development of large igneous provinces and some mantle plumes.
Explosive, hot volatile rich magma or volcanic eruptions are referred to generally as diatremes. Diatremes are not usually associated with diapirs, as they are small-volume magmas which ascend by volatile plumes, not by density contrast with the surrounding mantle.
Usage examples of "diapir".
In nearby regions of the Massif Central we see even more clearly the workings of intracrustal metamorphism, the anatexis engendered above one or more ascending asthenospheric diapirs.
This close to Chaos Central there would have to be diapirs, and kraken hated diapirs .
This diapir was about fifteen klicks across and rising rapidly as it approached the surface cap.
A diapir was nothing more than a blob of warm ice, heated by the vents and gravitational hot zones far below, rising through the Epsom-salt sea toward the ice cap that had once covered 100 percent of Europa and which now, two thousand e-years after the cryobot arbeiter company arrived, still covered more than 98 percent of the moon.
After a moment the ascending diapir pinched off from below and its matter formed a reservoir at the deepest part of Clyde's lithospheric mantle.
In a few minutes the diapir itself would mush into the thick cap ice, flow upward through fissures, lentinculae and leads, and bubble slush ice in a fountain a hundred meters high.