A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across
- planar wall rock structures, such as bedding or foliation
- massive rock formations, like igneous/magmatic intrusions and salt diapirs.
Dikes can therefore be either intrusive or sedimentary in origin.
Magmatic dikes
Sometimes dikes appear as swarms, consisting of several to hundreds of dikes emplaced more or less contemporaneously during a single intrusive event. The world's largest dike swarm is the Mackenzie dike swarm in the Northwest Territories, Canada.
Dikes often form as either radial or concentric swarms around plutonic intrusives, volcanic necks or feeder vents in volcanic cones. The latter are known as ring dikes.
Dikes can vary in texture and their composition can range from diabase or basaltic to granitic or rhyolitic, but on a global perspective the basaltic composition prevails, manifesting ascent of vast volumes of mantle-derived magmas through fractured lithosphere throughout Earth history. Pegmatite dikes are extremely coarse crystalline granitic rocks often associated with late stage granite intrusions or metamorphic segregations. Aplite dikes are fine grained or sugary textured intrusives of granitic composition.
Sedimentary dikes
Sedimentary dikes or clastic dikes are vertical bodies of sedimentary rock that cut off other rock layers. They can form in two ways:- When a shallow unconsolidated sediment is composed of alternating coarse grained and impermeable clay layers the fluid pressure inside the coarser layers may reach a critical value due to lithostatic overburden. Driven by the fluid pressure the sediment breaks through overlying layers and forms a dike.
- When a soil is under permafrost conditions the pore water is totally frozen. When cracks are formed in such rocks, they may fill up with sediments that fall in from above. The result is a vertical body of sediment that cuts through horizontal layers: a dike.
See also
- Batholith
- Ring dike
- Fissure vent
- Laccolith
- Runamo, formerly interpreted as a runic inscription.
- Dike swarm
- Sill
References
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Last updated on Monday June 09, 2008 at 21:31:24 PDT (GMT -0700)
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