A pegmatite is an igneous rock, formed by slow crystallization at high temperature and pressure at depth, and exhibiting large interlocking crystals usually greater in size than 25 mm (0.98 in). Most pegmatites are intrusive rocks found in sheets of rock near large masses of igneous rocks called batholiths.
A batholith is a large mass of intrusive igneous rock, larger than 100 km2 (40 sq mi) in area, that forms from cooled magma deep in Earth's crust. Batholiths are almost always made mostly of felsic or intermediate rock types, such as granite, quartz monzonite, or diorite.
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 less dense than the surrounding country rock, which produces buoyant forces on the magma that tend to drive it upwards. If the magma finds a path 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.
A dike or dyke, in geological usage, is a sheet of rock that is formed in a fracture of a pre-existing rock body. Dikes can be either magmatic or sedimentary in origin. Magmatic dikes form when magma flows into a crack then solidifies as a sheet intrusion, either cutting across layers of rock or through a contiguous mass of rock. Clastic dikes are formed when sediment fills a pre-existing crack.
Diabase, also called dolerite or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine grained to aphanitic chilled margins which may contain tachylite. Diabase is the preferred name in North America, while dolerite is the preferred name in the rest of the English-speaking world, where sometimes the name diabase is applied to altered dolerites and basalts. Some geologists prefer the name microgabbro to avoid this confusion.
A laccolith is a shallow, typically mushroom-shaped igneous intrusion that has deformed the overlying host rock dominantly by folding. They form after an initial sheet-like intrusion has been injected within or between layers of sedimentary rock. The pressure of the magma is high enough that the overlying strata are forced upward and folded, giving the laccolith a dome or mushroom-like form with a generally planar base. Over time, erosion can form small hills and even mountains around a central peak since the magma rock is likely more resistant to weathering than the host rock. The growth of laccoliths can take as little as a few months when associated with a single magma injection event, or up to hundreds or thousands of years by multiple magmatic pulses stacking sills on top of each other and deforming the host rock incrementally.
In geology, a sill is a tabular sheet intrusion that has intruded between older layers of sedimentary rock, beds of volcanic lava or tuff, or along the direction of foliation in metamorphic rock. A sill is a concordant intrusive sheet, meaning that a sill does not cut across preexisting rock beds. Stacking of sills builds a sill complex and a large magma chamber at high magma flux. In contrast, a dike is a discordant intrusive sheet, which does cut across older rocks. Sills are fed by dikes, except in unusual locations where they form in nearly vertical beds attached directly to a magma source. The rocks must be brittle and fracture to create the planes along which the magma intrudes the parent rock bodies, whether this occurs along preexisting planes between sedimentary or volcanic beds or weakened planes related to foliation in metamorphic rock. These planes or weakened areas allow the intrusion of a thin sheet-like body of magma paralleling the existing bedding planes, concordant fracture zone, or foliations.
Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form intrusions, such as batholiths, dikes, sills, laccoliths, and volcanic necks.
A diapir 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.
The Whin Sill or Great Whin Sill is a tabular layer of the igneous rock dolerite in County Durham, Northumberland and Cumbria in the northeast of England. It lies partly in the North Pennines Area of Outstanding Natural Beauty and partly in Northumberland National Park and stretches from Teesdale northwards towards Berwick.
In geology, an igneous 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 compositions, illustrated by examples like the Palisades Sill of New York and New Jersey; the Henry Mountains of Utah; the Bushveld Igneous Complex of South Africa; Shiprock in New Mexico; the Ardnamurchan intrusion in Scotland; and the Sierra Nevada Batholith of California.
The Palisades Sill is a Triassic, 200 Ma diabase intrusion. It extends through portions of New York and New Jersey. It is most noteworthy for The Palisades, the cliffs that rise steeply above the western bank of the Hudson River. The ideal location and accessibility of the sill, as well as its unique features, have generated much attention from nature enthusiasts, rock climbers, and geologists alike.
In geology, a chonolith is a type of igneous rock intrusion. Igneous rock intrusions are bodies of igneous rock that are formed by the crystallization of cooled magma below the Earth’s surface. These formations are termed intrusive rocks due the magma intruding rock layers but never reaching the earth’s surface. However, sometimes portions of plutons can become exposed at the Earth’s surface and thus the minerals can be observed since they are large enough. The different plutonic formations are named based on the different shapes that the cooled crystallized magma takes. However, all plutonic formations that have irregular shapes and do not share the same characteristics as other plutonic structures are termed chonoliths. Other plutonic structures that have specific shapes include: dikes, sills, laccoliths and sheets. Another unique characteristic of chonoliths is that there is a floor or base present which is typically absent in other types of intrusions.
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.
A sheet intrusion, or tabular intrusion, is a planar sheet of roughly the same thickness, that forms inside a pre-existing rock. When it cuts into another unlayered mass, or across layers, it is called a "dike". When it is formed between layers in a layered rock mass, it is called a "sill".
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.
The Southern Oklahoma Aulacogen(ah-lah-coh-jin) (help·info) is a failed rift, or failed rift arm (aulacogen), of the triple junction that became the Iapetus Ocean spreading ridges. It is a significant geological feature in the Western and Southern United States. It formed sometime in the early to mid Cambrian Period and spans the Wichita Mountains, Taovayan Valley, Anadarko Basin, and Hardeman Basin in Southwestern Oklahoma. The Southern Oklahoma Aulacogen is primarily composed of basaltic dikes, gabbros, and units of granitic rock.
A geological contact is a boundary which separates one rock body from another. A contact can be formed during deposition, by the intrusion of magma, or through faulting or other deformation of rock beds that brings distinct rock bodies into contact.
The Roosevelt Gabbros are an intrusive igneous geological formation in southwestern Oklahoma. They are one of two formations recognized in the Raggedy Mountain Gabbro Group, the other being the Glen Mountain Layered Complex. The Roosevelt Gabbros are generally characterized as biotite gabbros, which form many dikes and sills through the older Glen Mountain Layered Complex. They are named after the town of Roosevelt in Kiowa County, Oklahoma.
Volcanic and igneous plumbing systems (VIPS) consist of interconnected magma channels and chambers which are responsible for the production, storage and transportation of magma in Earth's crust. Volcanic plumbing systems can be found in all active tectonic settings, such as mid-oceanic ridges, subduction zones, and mantle plumes, when magmas generated in continental lithosphere, oceanic lithosphere, and in the sub-lithospheric mantle are transported. Magma is first generated by partial melting, followed by segregation and extraction from the source rock to separate the melt from the solid. As magma propagates upwards, a self-organised channelled network of magma channels develops due to buoyancy, transporting the melt from lower crust to upper regions. Channelled ascent mechanisms include the formation of dykes and ductile fractures that transport the melt in conduits. For bulk transportation, diapirs carries a large volume of melt and ascent through the crust. When magma stops ascending, or when magma supply stops, magma emplacement occurs. Different mechanisms of emplacement result in different structures, including plutons, sills, laccoliths and lopoliths.
