Dike (geology)

Dykes (English) or dikes ( American) are plate-like, often far-reaching body of rock from igneous rock, fill the larger gaps and overlap or intersect the surrounding rock. The term has partially replaced lately the German term dyke, which differs in some areas of geological jargon from the Anglo-American concept. A special form of dykes are of sedimentary origin.

Manifestations of magmatic Dykes

The discordant nature of the igneous dykes causes various forms:

• Multiple Dykes are coherent body of rock that have formed predominantly of multiple intrusions of the same material. Example of this form are the Sheeted Dike complexes of the oceanic crust, which are composed of numerous, nested Doleritgängen.
• Composite Dykes are coherent body of rock that have been formed from multiple intrusions of different materials. For example, an original, silicon- poor dolerite dyke at a later stage to be intruded by a silicon-richer Kersantit.
• Ring dykes cut the earth's surface annular, circular or arcuate
• " Cone Sheets" are ring gears that match a set at an angle cone, ie become narrower with increasing depth. They arise when a caldera intrusion by the obtrude of magma in the resulting annular fractures.

Igneous rocks average sized Dykes have a mean grain size, the one smaller Dykes is predominantly fine -grained, very large Dykes rather grainy. This is due to the different gel time, which is responsible for the size of the crystals formed.

Sedimentary Dykes

A special form of dykes are of sedimentary origin, the so-called sedimentary or clastic dykes. These may result from different mechanisms by sediment from below, from the side or from above penetrates into columns that have affected them in the sediment or sedimentary rock formed. So far, inter alia, the following mechanisms for the formation of columns, and thus of sedimentary Dykes been proposed:

• Different setting of sediment under a coat or over basement structures, thereby formation of columns
• Slipping of sediment on a slope or similar gravitational instabilities
• Interference activity during the deposition of sediments
• Earthquake.

The filling of the columns from the top is done in the ordinary course of sedimentation. Actively involved in the development of sediment- filled columns, the Füllsediment is mind if in an out alternately drained, not fully solidified rock package - about a sequence of sandstones and shales - is greater than the breaking strength of the overlying impermeable rock the pore water pressure, or elevated pore water pressure a sudden pressure change occurs, such as in an earthquake. Coarse-grained and permeable material that is mobilized due to the large pore volume, penetrates from below into emerging weakness zones or fractures in the impermeable rock on.

A subset of the sedimentary dykes are the Neptunian Dykes, caused by the mostly downward filling of gaps in carbonate rocks.

Occurrence

Magmatic dykes are usually in front along with larger igneous rock bodies, often forming large flocks of radial or parallel structure ( vein swarm ). One of the biggest Dyke occurrence in Europe is the Hebridean vein swarm with almost 600 km extension in Ireland, Northern England and Scotland. Other occurrences are of about 500 km long Great Dyke in Zimbabwe, Mackenzie Dike Swarm in the Northwest Territories of Canada, or the formerly contiguous Dykes in the Large Igneous Province of the Karoo basalts in South Africa, in the Ferrar Group at the Ross Sea in find Antarctica and in the volcanic Chon Aike province of Patagonia. , Local occurrence in further spreading around the world. In Germany Dykes are open-minded about the young volcanic regions of the volcanic Eifel, as individual or group deposits in the Rhenish Slate Mountains and in many other areas.