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A dome is a feature in
structural geology Structural geology is the study of the three-dimensional distribution of rock units with respect to their deformational histories. The primary goal of structural geology is to use measurements of present-day rock geometries to uncover informati ...
where a circular part of the Earth's surface has been pushed upward, tilting the pre-existing layers of earth away from the center. In technical terms, it consists of symmetrical
anticline In structural geology, an anticline is a type of Fold (geology), fold that is an arch-like shape and has its oldest Bed (geology), beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex curve, c ...
s that intersect each other at their respective apices. Intact, domes are distinct, rounded,
spherical A sphere (from Ancient Greek, Greek , ) is a surface (mathematics), surface analogous to the circle, a curve. In solid geometry, a sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three ...
-to-
ellipsoid An ellipsoid is a surface that can be obtained from a sphere by deforming it by means of directional Scaling (geometry), scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface;  that is, a Surface (mathemat ...
al-shaped protrusions on the Earth's surface. A slice parallel to Earth's surface of a dome features concentric rings of
strata In geology and related fields, a stratum (: strata) is a layer of Rock (geology), rock or sediment characterized by certain Lithology, lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by v ...
. If the top of a dome has been eroded flat, the resulting structure in
plan view In technical drawing and computer graphics, a multiview projection is a technique of illustration by which a standardized series of orthographic projection, orthographic two-dimensional pictures are constructed to represent the form of a three-d ...
appears as a bullseye, with the youngest rock layers at the outside, and each ring growing progressively older moving inwards. These strata would have been horizontal at the time of deposition, then later deformed by the uplift associated with dome formation.


Formation mechanisms

There are many possible mechanisms responsible for the formation of domes, the foremost of which are refolding, diapirism, igneous intrusion, and post-impact uplift.


Refolding

Structural domes can be formed by horizontal stresses in a process known as refolding, which involves the superposition, or overprinting, of two- or more fold fabrics. Upright folds formed by a horizontal primary stress in one direction can be altered by another horizontal stress oriented at 90 degrees to the original stress. This results in overprinting of the twofold fabrics, similar to
wave interference In physics, interference is a phenomenon in which two coherent waves are combined by adding their intensities or displacements with due consideration for their phase difference. The resultant wave may have greater amplitude (constructive in ...
patterns, that results in a system of basins and domes. Where the
syncline In structural geology, a syncline is a fold with younger layers closer to the center of the structure, whereas an anticline is the inverse of a syncline. A synclinorium (plural synclinoriums or synclinoria) is a large syncline with superimposed ...
s of both fabrics are superimposed, a basin is formed; however, where the anticlines of both fabrics are superimposed, a dome is formed.


Diapirism

Diapirism involves the vertical displacement of a parcel of material through overlying strata in order to reach equilibrium within a system that has an established density gradient (see Rayleigh–Taylor instability). To reach equilibrium, parcels from a stratum composed of less-dense material will rise towards Earth's surface, creating formations that are most often expressed in cross-section as "tear drop"-shaped, where the rounded end is that closest to the surface of the overlying strata. If overlying strata are weak enough to deform as the parcel rises, a dome can form; in cases where the overlying strata are particularly devoid of resistance to applied stress, the
diapir A diapir (; , ) 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 ...
may penetrate through the strata altogether and erupt on the surface. Potential materials comprised by these less-dense strata include salt (which is highly incompressible, thus creating the structural instability that leads to diapirism when buried under deposited strata and subject to overlying stress) and partially melted
migmatite Migmatite is a composite rock (geology), rock found in medium and high-grade metamorphic environments, commonly within Precambrian craton, cratonic blocks. It consists of two or more constituents often layered repetitively: one layer is an old ...
(a metamorphic-texture rock frequently found in domes due to the typical involvement of heat and/or pressure with their formation).


Igneous intrusion

The
intrusion In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...
of
magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...
into layered
sedimentary rock Sedimentary rocks are types of rock (geology), rock formed by the cementation (geology), cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or de ...
s and the resulting formation of
laccolith A laccolith is a body of intrusive rock with a dome-shaped upper surface and a level base, fed by a conduit from below. A laccolith forms when magma (molten rock) rising through the Earth's crust begins to spread out horizontally, prying apart ...
s or igneous stocks can also create domes. In the case of laccoliths, this happens when the vertical movement magma stops at the base of particular sedimentary layer or layers and starts to spread laterally away from the pipe of ascending magma. As the magma flows laterally from the pipe of magma feeding it, a mushroom-shaped mass of magma is formed. This causes the overlying layers of sedimentary rock to bulge upward like a giant blister and deform into a dome.


Post-impact uplift

A
complex crater Complex craters are a type of large impact crater morphology. Complex craters are classified into two groups: ''central-peak craters'' and '' peak-ring craters''. Peak-ring craters have diameters that are larger in than central-peak craters and ...
, caused by collision of a
hypervelocity Hypervelocity is very high velocity, approximately over 3,000 meters per second (11,000 km/h, 6,700 mph, 10,000 ft/s, or Mach 8.8). In particular, hypervelocity is velocity so high that the strength of materials upon impact is v ...
body with another larger than itself, is typified by the presence of a dome at the centre of the site of impact. These domes are typically large-scale (on the magnitude of tens of metres) and thought to be the result of post-impact weakening of the overlying strata and basement. Weakening is integral for the vertical uplift required to create a dome to take place, as it allows vertical displacement to happen unconstrained by the original rigidity properties of the undeformed rock. This displacement is the result of the parcel of rock at the centre of the site of impact, composed of the strata and
basement A basement is any Storey, floor of a building that is not above the grade plane. Especially in residential buildings, it often is used as a utility space for a building, where such items as the Furnace (house heating), furnace, water heating, ...
, re-equilibrating relative to gravity. Earlier theories attributed the dome-forming uplift to rebound; however, this would imply that the rock deforms elastically. Elastic deformation is not likely being that an impact is accompanied by extensive fracturing and partial melting of the rock that would change the mechanical properties of the rock.


Examples


Structural domes

*Observed in the Karatau fault system, Kazakhstan *North Pole Dome, Western Australia (in the Pilbara Craton)


Diapiric domes

* Gorleben salt dome, Lüchow-Dannenberg district in the far north-east of
Lower Saxony Lower Saxony is a States of Germany, German state (') in Northern Germany, northwestern Germany. It is the second-largest state by land area, with , and fourth-largest in population (8 million in 2021) among the 16 ' of the Germany, Federal Re ...
,
Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...
. * Leo Pargil Dome,
Himachal Pradesh Himachal Pradesh (; Sanskrit: ''himācāl prādes;'' "Snow-laden Mountain Province") is a States and union territories of India, state in the northern part of India. Situated in the Western Himalayas, it is one of the thirteen Indian Himalayan ...
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Tibet Tibet (; ''Böd''; ), or Greater Tibet, is a region in the western part of East Asia, covering much of the Tibetan Plateau and spanning about . It is the homeland of the Tibetan people. Also resident on the plateau are other ethnic groups s ...
an border


Igneous intrusion domes

* Henry Mountains,
Utah Utah is a landlocked state in the Mountain states, Mountain West subregion of the Western United States. It is one of the Four Corners states, sharing a border with Arizona, Colorado, and New Mexico. It also borders Wyoming to the northea ...
*
Richat Structure The Richat Structure, or ''Guelb er Richât'' (, ), is a prominent circular geological feature in the Adrar Plateau of the Sahara The Sahara (, ) is a desert spanning across North Africa. With an area of , it is the largest hot desert in ...
, central Mauritania; possible impact structure


Impact structures

* Upheaval Dome, Utah, USA * Vredefort Dome, South Africa


See also

* Dome illusion


References

{{Commons category, Natural domes Rock formations Structural geology Tectonic landforms