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In geology, an igneous intrusion (or intrusive body [1] or simply intrusion [2]) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth.
Intrusion is one of the two ways igneous rock can form. The other is extrusion, such as a volcanic eruption or similar event. An intrusion is any body of intrusive igneous rock, formed from magma that cools and solidifies within the crust of the planet. In contrast, an extrusion consists of extrusive rock, formed above the surface of the crust.
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 it does not cut across preexisting rock beds.
In geology, a dike or dyke 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.
In geology, a chonolith is a type of igneous rock intrusion (also known as pluton). 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 surface. [1]
It is the origin of this layer, and subsequently, the sill as a whole, that has generated much of the attention, as well as the varying origin theories proposed for the intrusion (see below). There is an average stratigraphic thickness of 300 meters (~1000 feet), with the famous cliffs rising 100 meters (300 ft) on average above sea level.
In geology, when an igneous intrusion cuts across a formation of sedimentary rock, it can be determined that the igneous intrusion is younger than the sedimentary rock. There are a number of different types of intrusions, including stocks, laccoliths , batholiths , sills and dikes .
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 km 2 (39 sq mi) to over 50,000 km 2 (19,000 sq mi) and several hundred metres to over one kilometre (3,300 ft) in thickness. [ 1 ]