Diapir

Last updated
diapirs in a subducting plate boundary Subduction-en.svg
diapirs in a subducting plate boundary

A diapir ( /ˈd.əpɪər/ ; [1] 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 tectonics 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.

French language Romance language

French is a Romance language of the Indo-European family. It descended from the Vulgar Latin of the Roman Empire, as did all Romance languages. French evolved from Gallo-Romance, the spoken Latin in Gaul, and more specifically in Northern Gaul. Its closest relatives are the other langues d'oïl—languages historically spoken in northern France and in southern Belgium, which French (Francien) has largely supplanted. French was also influenced by native Celtic languages of Northern Roman Gaul like Gallia Belgica and by the (Germanic) Frankish language of the post-Roman Frankish invaders. Today, owing to France's past overseas expansion, there are numerous French-based creole languages, most notably Haitian Creole. A French-speaking person or nation may be referred to as Francophone in both English and French.

Greek language language spoken in Greece, Cyprus and Southern Albania

Greek is an independent branch of the Indo-European family of languages, native to Greece, Cyprus and other parts of the Eastern Mediterranean and the Black Sea. It has the longest documented history of any living Indo-European language, spanning more than 3000 years of written records. Its writing system has been the Greek alphabet for the major part of its history; other systems, such as Linear B and the Cypriot syllabary, were used previously. The alphabet arose from the Phoenician script and was in turn the basis of the Latin, Cyrillic, Armenian, Coptic, Gothic, and many other writing systems.

Rayleigh–Taylor instability Unstable behavior of two contacting fluids of different densities

The Rayleigh–Taylor instability, or RT instability, is an instability of an interface between two fluids of different densities which occurs when the lighter fluid is pushing the heavier fluid. Examples include the behavior of water suspended above oil in the gravity of Earth, mushroom clouds like those from volcanic eruptions and atmospheric nuclear explosions, supernova explosions in which expanding core gas is accelerated into denser shell gas, instabilities in plasma fusion reactors and inertial confinement fusion.

Contents

A lava lamp illustrates Rayleigh-Taylor instability-type diapirism in which the tectonic stresses are low. 1990s Mathmos Astro.jpg
A lava lamp illustrates Rayleigh–Taylor instability-type diapirism in which the tectonic stresses are low.

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. [2]

Triton (moon) largest moon of Neptune

Triton is the largest natural satellite of the planet Neptune, and the first Neptunian moon to be discovered. The discovery was made on October 10, 1846, by English astronomer William Lassell. It is the only large moon in the Solar System with a retrograde orbit, an orbit in the direction opposite to its planet's rotation. At 2,710 kilometres (1,680 mi) in diameter, it is the seventh-largest moon in the Solar System, the only satellite of Neptune massive enough to be in hydrostatic equilibrium and the second-largest planetary moon in relation to its primary, after Earth's Moon. Because of its retrograde orbit and composition similar to Pluto's, Triton is thought to have been a dwarf planet captured from the Kuiper belt.

Europa (moon) The smallest of the four Galilean moons of Jupiter

Europa is the smallest of the four Galilean moons orbiting Jupiter, and the sixth-closest to the planet of all the 79 known moons of Jupiter. It is also the sixth-largest moon in the Solar System. Europa was discovered in 1610 by Galileo Galilei and was named after Europa, the Phoenician mother of King Minos of Crete and lover of Zeus.

Miranda (moon) smallest moon of Uranus

Miranda, also designated Uranus V, is the smallest and innermost of Uranus's five round satellites. It was discovered by Gerard Kuiper on 16 February 1948 at McDonald Observatory, and named after Miranda from William Shakespeare's play The Tempest. Like the other large moons of Uranus, Miranda orbits close to its planet's equatorial plane. Because Uranus orbits the Sun on its side, Miranda's orbit is perpendicular to the ecliptic and shares Uranus's extreme seasonal cycle.

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.[ citation needed ] 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.[ citation needed ]

The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ, although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume:

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.[ clarification needed ] Such overpressured Floaters pose a significant risk when trying to drill through them.[ clarification needed ] There is an analogy to a Galilean thermometer. [3]

Well drilling

Well drilling is the process of drilling a hole in the ground for the extraction of a natural resource such as ground water, brine, natural gas, or petroleum, for the injection of a fluid from surface to a subsurface reservoir or for subsurface formations evaluation or monitoring. Drilling for the exploration of the nature of the material underground is best described as borehole drilling.

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.

Evaporite A water-soluble mineral sediment formed by evaporation from an aqueous solution

Evaporite is the term for a water-soluble mineral sediment that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as ocean deposits, and non-marine, which are found in standing bodies of water such as lakes. Evaporites are considered sedimentary rocks and are formed by chemical sediments.

Magma Mixture of molten or semi-molten rock, volatiles and solids that is found beneath the surface of the Earth

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 natural satellites. Besides molten rock, magma may also contain suspended crystals and gas bubbles. Magma is produced by melting of the mantle and/or the crust at various tectonic settings, including subduction zones, continental rift zones, mid-ocean ridges and hotspots. Mantle and crustal melts migrate upwards through the crust where they are thought to be stored in magma chambers or trans-crustal crystal-rich mush zones. During their storage in the crust, magma compositions may be modified by fractional crystallization, contamination with crustal melts, magma mixing, and degassing. Following their ascent through the crust, magmas may feed a volcano or solidify underground to form an intrusion. While the study of magma has historically relied on observing magma in the form of lava flows, magma has been encountered in situ three times during geothermal drilling projects—twice in Iceland, and once in Hawaii.

A mantle is a layer inside a planetary body bounded below by a core and above by a crust. Mantles are made of rock or ices, and are generally the largest and most massive layer of the planetary body. Mantles are characteristic of planetary bodies that have undergone differentiation by density. All terrestrial planets, a number of asteroids, and some planetary moons have mantles.

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.

Volatiles in planetary science, chemical elements or compounds with low boiling points associated with a planet’s or moon’s crust or atmosphere; e.g. nitrogen, water, carbon dioxide, ammonia, hydrogen, methane, sulfur dioxide

In planetary science, volatiles are the group of chemical elements and chemical compounds with low boiling points that are associated with a planet's or moon's crust or atmosphere. Examples include nitrogen, water, carbon dioxide, ammonia, hydrogen, methane and sulfur dioxide. In astrogeology, these compounds, in their solid state, often comprise large proportions of the crusts of moons and dwarf planets.

Diatreme A volcanic pipe formed by a gaseous explosion

A diatreme, sometimes known as a maar-diatreme volcano, is a volcanic pipe formed by a gaseous explosion. When magma rises up through a crack in the Earth's crust and makes contact with a shallow body of ground water, rapid expansion of heated water vapor and volcanic gases can cause a series of explosions. A relatively shallow crater is left and a rock filled fracture in the Earth's crust. Diatremes breach the Earth's surface and produce a steep inverted cone shape.

Economic importance of diapirs

Geological cross section through the Northwestern Basin of Germany (Ostfriesland-Nordheide). Salt domes have penetrated younger layers and moved near to the surface. They sometimes form pockets where petroleum and natural gas can collect. Excavated salt domes are also used for underground storage. Salt dome hg.png
Geological cross section through the Northwestern Basin of Germany (Ostfriesland-Nordheide). Salt domes have penetrated younger layers and moved near to the surface. They sometimes form pockets where petroleum and natural gas can collect. Excavated salt domes are also used for underground storage.

Diapirs or piercement structures are structures resulting from the penetration of overlaying material. By pushing upward and piercing overlying rock layers, diapirs can form anticlines, salt domes and other structures capable of trapping petroleum and natural gas. Igneous intrusions themselves are typically too hot to allow the preservation of preexisting hydrocarbons. [4]

See also

Related Research Articles

Granite A common type of intrusive, felsic, igneous rock with granular structure

Granite is a common type of felsic intrusive igneous rock that is granular and phaneritic in texture. Granites can be predominantly white, pink, or gray in color, depending on their mineralogy. The word "granite" comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a holocrystalline rock. Strictly speaking, granite is an igneous rock with between 20% and 60% quartz by volume, and at least 35% of the total feldspar consisting of alkali feldspar, although commonly the term "granite" is used to refer to a wider range of coarse-grained igneous rocks containing quartz and feldspar.

Batholith

A batholith is a large mass of intrusive igneous rock, larger than 100 square kilometres (40 sq mi) in area, that forms from cooled magma deep in the Earth's crust. Batholiths are almost always made mostly of felsic or intermediate rock types, such as granite, quartz monzonite, or diorite.

Breccia Rock composed of broken fragments cemented by a matrix

Breccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix that can be similar to or different from the composition of the fragments.

Volcanism phenomena and processes associated with the action of volcanos, geysers and fumaroles

Volcanism is the phenomenon of eruption of molten rock (magma) onto the surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics and volcanic gases erupt through a break in the surface called a vent. It includes all phenomena resulting from and causing magma within the crust or mantle of the body, to rise through the crust and form volcanic rocks on the surface.

Crust (geology) The outermost solid shell of a rocky planet, dwarf planet, or natural satellite

In geology, the crust is the outermost solid shell of a rocky planet, dwarf planet, or natural satellite. It is usually distinguished from the underlying mantle by its chemical makeup; however, in the case of icy satellites, it may be distinguished based on its phase.

Planetary differentiation

In planetary science, planetary differentiation is the process of separating out different constituents of a planetary body as a consequence of their physical or chemical behavior, where the body develops into compositionally distinct layers; the denser materials of a planet sink to the center, while less dense materials rise to the surface, generally in a magma ocean. Such a process tends to create a core and mantle. Sometimes a chemically distinct crust forms on top of the mantle. The process of planetary differentiation has occurred on planets, dwarf planets, the asteroid 4 Vesta, and natural satellites.

Magma chamber Accumulation of molten rock within the Earts crust

A magma chamber is a large pool of liquid rock beneath the surface of the Earth. The molten rock, or magma, in such a chamber is under great pressure, and, given enough time, that pressure can gradually fracture the rock around it, creating a way for the magma to move upward. If it finds its way to the surface, then the result will be a volcanic eruption; consequently, many volcanoes are situated over magma chambers. These chambers are hard to detect deep within the Earth, and therefore most of those known are close to the surface, commonly between 1 km and 10 km down.

Salt dome geological structure

A salt dome is a type of structural dome formed when a thick bed of evaporite minerals found at depth intrudes vertically into surrounding rock strata, forming a diapir. It is important in petroleum geology because salt structures are impermeable and can lead to the formation of a stratigraphic trap.

Intrusive rock intrusive volcanic rocks

Intrusive rock is formed when magma crystallizes and solidifies underground to form intrusions, for example plutons, batholiths, dikes, sills, laccoliths, and volcanic necks.

Large igneous province Huge regional accumulation of igneous rocks

A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive and extrusive, arising when magma travels through the crust towards the surface. The formation of LIPs is variously attributed to mantle plumes or to processes associated with divergent plate tectonics. The formation of some of the LIPs the past 500 million years coincide in time with mass extinctions and rapid climatic changes, which has led to numerous hypotheses about the causal relationships. LIPs are fundamentally different from any other currently active volcanoes or volcanic systems.

Rock cycle Transitions through geologic time among the three main rock types: sedimentary, metamorphic, and igneous

The rock cycle is a basic concept in geology that describes the transitions through geologic time among the three main rock types: sedimentary, metamorphic, and igneous. As the adjacent diagram illustrates, each of the types of rocks is altered or destroyed when it is forced out of its equilibrium conditions. An igneous rock such as basalt may break down and dissolve when exposed to the atmosphere, or melt as it is subducted under a continent. Due to the driving forces of the rock cycle, plate tectonics and the water cycle, rocks do not remain in equilibrium and are forced to change as they encounter new environments. The rock cycle is an illustration that explains how the three rock types are related to each other, and how processes change from one type to another over time. This cyclical aspect makes rock change a geologic cycle and, on planets containing life, a biogeochemical cycle.

Layered intrusion large sill-like body of igneous rock

A layered intrusion is a large sill-like body of igneous rock which exhibits vertical layering or differences in composition and texture. These intrusions can be many kilometres in area covering from around 100 km2 (39 sq mi) to over 50,000 km2 (19,000 sq mi) and several hundred metres to over one kilometre (3,300 ft) in thickness. While most layered intrusions are Archean to Proterozoic in age, they may be any age such as the Cenozoic Skaergaard intrusion of east Greenland or the Rum layered intrusion in Scotland. Although most are ultramafic to mafic in composition, the Ilimaussaq intrusive complex of Greenland is an alkalic intrusion.

Country rock (geology)

Country rock is a geological term meaning the rock native to an area, in which there is an intrusion of viscous geologic material, commonly magma, or perhaps rock salt or unconsolidated sediments.

Sierra Nevada Batholith Sierra Nevada Batholith is a large batholith, Sierra Nevada mountain range, USA, United States

The Sierra Nevada Batholith is a large batholith which forms the core of the Sierra Nevada mountain range in California, exposed at the surface as granite.

Igneous rock Rock formed through the cooling and solidification of magma or lava

Igneous rock, 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 or lava. The magma can be derived from partial melts of existing rocks in either a planet's mantle or crust. Typically, the melting is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition. Solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive rocks. Igneous rock may form with crystallization to form granular, crystalline rocks, or without crystallization to form natural glasses. Igneous rocks occur in a wide range of geological settings: shields, platforms, orogens, basins, large igneous provinces, extended crust and oceanic crust.

The methods of pluton emplacement are the ways magma is accommodated in a host rock where the final result is a pluton. The methods of pluton emplacement are not yet fully understood, but there are many different proposed pluton emplacement mechanisms. Stoping, diapirism and ballooning are the widely accepted mechanisms. There is now evidence of incremental emplacement of plutons.

Okavango Dyke Swarm

The Okavango Dyke Swarm is a giant dyke swarm of the Karoo Large Igneous Province in northeast Botswana, southern Africa. It consists of a group of Proterozoic and Jurassic dykes, trending east-southeast across Botswana, spanning a region nearly 2,000 kilometres (1,200 mi) long and 110 kilometres (68 mi) wide. The Jurassic dykes were formed approximately 179 million years ago, composed of mainly tholeiitic mafic rocks. The formation is related to the magmatism at the Karoo triple junction, induced by the plate tectonic break up of the Gondwana supercontinent in the early Jurassic.

Salt deformation

Salt deformation is the change of shape of natural salt bodies in response to forces and mechanisms that controls salt flow. Such deformation can generate large salt structures such as underground salt layers, salt diapirs or salt sheets at the surface. Strictly speaking, salt structures are formed by rock salt that is composed of pure halite (NaCl) crystal. However, most halite in nature appears in impure form, therefore rock salt usually refers to all rocks that composed mainly of halite, sometimes also as a mixture with other evaporites such as gypsum and anhydrite. Earth's salt deformation generally involves such mixed materials.

References

  1. American Heritage Dictionary of the English Language (Fourth Edition. Houghton Mifflin, 2000). "Archived copy". Archived from the original on 2006-12-08. Retrieved 2006-12-20.CS1 maint: Archived copy as title (link).
  2. Cassini Imaging Central Laboratory for Operations, Enceladus Rev 80 Flyby: Aug 11 '08. Retrieved 2008-08-15.
  3. Don L. Anderson (2007). "The eclogite engine: Chemical geodynamics as a Galileo thermometer". In Gillian R. Foulger, Donna M. Jurdy. Plates, plumes, and planetary processes; Volume 430 of Special Papers. American Geological Society. ISBN   0-8137-2430-9.
  4. Schlumberger Oilfield Glossary, on-line at . Retrieved 2008-08-15.