Current state of plate tectonics
Over the past decade, plate tectonics has substantially changed its basic position. Now they can be formulated as follows:
The upper part of the solid Earth is divided into brittle lithosphere and plastic asthenosphere. Convection in the asthenosphere - the main cause of plate movement.
Modern lithosphere is divided into 8 large plates, dozens of medium-sized plates and many smaller ones. Small plates are located in zones between the major plates. Seismic, tectonic and magmatic activity is concentrated on the plate boundaries.
Plates in the first approximation described as rigid bodies, and their movement obeys Euler's rotation theorem.
There are three basic types of relative movement of plates
1. divergence (divergence), expressed rifting and seafloor spreading;
2. convergence (convergence) expressed subduction and collision;
3. shear displacement on the transform geological faults.
Seafloor spreading in the oceans is compensated subduction and collision along the periphery and the radius and volume of the earth is constant to within a thermal compression of the planet (in any case, the mean temperature of the Earth's interior slowly, over billions years, decreases). The constancy of the size of the Earth continuously refuted, but attempts to prove the significant changes the size of the planet have not been substantiated.
Movement of tectonic plates caused by their enthusiasm convective flow in the asthenosphere.
There are two fundamentally different types of crust - continental crust (more ancient) and the oceanic crust (not older than 200 million years). Some of lithospheric plates are composed entirely of oceanic crust (example - the largest Pacific Plate), while others consist of a block of continental crust, oceanic crust in the soldered.
Over 90% of the Earth's surface in the modern era is covered 8 major lithospheric plates:
Australian plate
Antarctic Plate
African Plate
Eurasian plate
Indian Plate
Pacific Plate
North American Plate
South American Plate
Among medium-sized plates can be distinguished Arabian Peninsula and the Cocos Plate and the Juan de Fuca plate, the remains of a huge slab Faralon making up a considerable portion of the bottom of the Pacific, but now disappeared into the subduction zone under the North and South America.