Island arc
An island arc is a geotectonic structure of the earth's crust in the form of recent or original islands or island chains. It is produced in processes of plate tectonics, when an oceanic plate under another oceanic plate dives ( subduction ). The arc-like course of the islands and island chains caused by the geometry of the Earth's surface in the zone in which bends a lithospheric plate and is pushed into a certain angle under another plate. Island arcs are unstable systems and certificates of intense magmatism.
Formation
The shape of the island arcs is due to the geometry of spheres pieces on a spherical surface. If one makes a small incision in a table tennis ball and then pushing the patch, create a curved bend, the curvature shows the cut away.
Along these kinks occurs in the earth's crust breaks and columns. Uppermost sediment residues are often of the subducting plate sheared, which are accumulated on the plate edge of the overlying plate ( accretionary prism ). In addition, the friction of the two plates produces a high temperature. The sediments on the plate and their altered rocks contain a lot of water. By the action of heat and pressure, it is released and moves upwards. There it leads in the shell material of the top plate in a lowering of the melting point. Thus this is partially melted to form magma. As the magma is hot, it has a lower density than the surrounding rock. This is similar to air in a hot air balloon. It rises and eventually reaches the surface, where volcanoes and plutons occur. Island arcs are therefore of volcanic origin. Typical of island arcs are adjacent to active volcanoes their greenish- black beaches. They consist of the eroded basalt material of the volcanic cone.
On the ocean side of the island arc, where the subducted plate dives beneath the overlying plate, there is a deep groove. The part between the deep sea channel and the island arc is called Fore - Arc, the located on the other side of the island arc part as a back-arc.
The shear stress can also simultaneously cause a parallel shift of the side plate edges, creating a stretch of the island arc is done.
Immerse an oceanic plate under a continental plate, usually no island arc, but a volcanic belt in the folded mountain range formed by the collision, as eg is the case in the Andes.
Selection of island arcs
- Aleutian Islands
- Cyclades arc
- Kuril
- Japan
- Philippines
- Mariana
- The South Sandwich Islands
- Sunda arc
- Solomon Islands
- Antilles
Weblink
- Jean -Pierre Burg: Kohistan - Western Himalayas: island arc - continent collision. Zurich 2011 (PDF, 1.5 MB)
- Geographical term
- Volcanism
- Plutonism
- Plate tectonic