A diapir (; , ) is a type of
igneous 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
The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United S ...
to narrow
dikes of material that move along tectonically induced fractures in surrounding rock.
The term was introduced by the
Romanian geologist
A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, alt ...
Ludovic Mrazek, who was the first to understand the principle of
salt tectonics and
plasticity. The term ''diapir'' may be applied to
igneous
Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma o ...
structures, but it is more commonly applied to non-igneous, relatively cold materials, such as
salt domes and
mud diapirs.
Occurrence
Differential loading
Differential may refer to:
Mathematics
* Differential (mathematics) comprises multiple related meanings of the word, both in calculus and differential geometry, such as an infinitesimal change in the value of a function
* Differential algebra
* ...
causes salt deposits covered by
overburden (
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...
) 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
Enceladus is the sixth-largest moon of Saturn (19th largest in the Solar System). It is about in diameter, about a tenth of that of Saturn's largest moon, Titan. Enceladus is mostly covered by fresh, clean ice, making it one of the most refle ...
, and Uranus's moon
Miranda.
Formation mechanisms
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''.
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
Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natura ...
assembles. Diapirism in the
mantle
A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that.
Mantle may refer to:
*Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear
**Mantle (vesture), an Eastern Orthodox ve ...
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.
Economic importance
Diapirs or piercement structures are structures resulting from the penetration of overlaying material. By pushing upward and piercing overlying rock layers, diapirs can form
anticline
In structural geology, an anticline is a type of fold that is an arch-like shape and has its oldest beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex up in which the hinge or crest is the ...
s (arch-like shape
fold
Fold, folding or foldable may refer to:
Arts, entertainment, and media
* ''Fold'' (album), the debut release by Australian rock band Epicure
*Fold (poker), in the game of poker, to discard one's hand and forfeit interest in the current pot
*Above ...
s),
salt domes (mushroom/
dome-shaped diapirs), and other structures capable of trapping
hydrocarbons
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
such as
petroleum
Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...
and
natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbon ...
. Igneous intrusions themselves are typically too hot to allow the preservation of preexisting
hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
s.
[Schlumberger Oilfield Glossary, on-line a]
. Retrieved 2008-08-15.
See also
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References
{{reflist
Economic geology
Geological processes
Intrusions
Salt domes
Structural geology
Structure of the Earth