Lithosphere

The lithosphere [ litosfɛ ː rə ] ( solid rock shell, from Greek λίθος líthos ' stone ' and σφαίρα Sphaera ball ') forms in the rheological model of the Earth's interior, the outermost layer of the earth. It includes the crust and the outermost part of the mantle, the lithospheric mantle, and their mechanical properties can be simply referred to as elastic.

Layout and Organization

The detectable using seismological investigations interface between crust and lithospheric mantle is the underlying as Mohorovičić discontinuity (short: Moho ) refers. At her an abrupt increase in the wave velocity due to the density difference between the crust and the mantle rocks. Below the spreading zone of a mid-ocean ridge, the Moho directly indicates the transition to the asthenosphere, as they have no lithospheric mantle.

The asthenosphere is the part of the upper mantle, which follows after the rheological model of the Earth below the lithosphere. While the rock of the lithosphere has an almost elastic behavior, the transition to the asthenosphere is characterized in that the material loses its elasticity and eventually ductile, comparable to an extremely viscous liquid, behaves. This manifests itself in seismological measurements in a decrease in the wave velocity at the transition from lithosphere to asthenosphere. This difference, elastic - ductile, is the main differentiator between lithosphere and asthenosphere.

The thickness of the lithosphere varies from a few kilometers along the mid-ocean ridges up to 100 km or 200 km for continents and is on average about 100 km. The Moho is located in the continental lithosphere at depths of 30-50 km. For strongly thickened crust, such as under a young fold mountains it is even at depths up to 70 km. In oceanic lithosphere at the Moho is in only 5-7 km depth.

The lithosphere is divided into seven major lithospheric plates, which exist in various proportions of continental and oceanic lithosphere. These are the North American Plate, the Eurasian Plate, the South American Plate, the African Plate, the Australian Plate, the Antarctic Plate and the Pacific Plate. There are also other, small plates, such as the Nazca plate and the Philippine plate. Also can be referred to the large plates further subdivided into several smaller plates. All these plates are on the asthenosphere and are in constant, albeit in human time scales barely perceptible movement.

Dynamics

The simplified elastic as to be considered plates "float " on the comparatively ductile asthenosphere (see → isostasy ). You are in constant motion with relative speeds up to 10 cm per year. As a cause of continental drift thermal convection currents in the mantle are assumed.

The dynamics of the lithosphere is generally referred to as plate tectonics. In terms of plate motions are distinguished three different modes:

• Convergent ( towards each other drifting ) plates with sliding down the oceanic lithosphere beneath another lithospheric plate ( subduction ), which deep-sea trenches and volcanically active mountain ranges occur ( for example, Japanese Islands and Japan Trench, Andes and Peru or Atacama Trench ).
• Or formation of fold mountains by collision of two continental blocks (eg Himalayas, Alps). Here, the crust is often one of the two disks involved from the lithospheric mantle separated ( delamination ).

As a result of plate tectonics can be found in all plate boundaries always earthquakes and volcanism often. In addition to differ continental and oceanic crust at her age. While oceanic crust due to subduction is usually only 160-190 million years old, there are continental crust, which is 4 billion years old.