Home >> Science & Nature >> Nature

Properties of Plate Tectonics

Plate tectonics, also known as continental drift, seeks to explain the nature and movement of the Earth's crust. This crust has been fractured into large pieces, called plates. The tectonic process explains how these plates move and interact along plate boundaries. This interaction between plates is responsible for the creation of new crust and the destruction of old crust. Plate tectonics is also responsible for all the Earth's major geological features.

Tectonic Plates
- There are two types of tectonic plates: oceanic and continental. Oceanic plates, which cover 71 percent of the planet, are mafic in composition, meaning they are high in iron and magnesium. This makes them much denser than continental plates. Continental plates, which cover 29 percent of the planet, are felsic in nature, making them more buoyant than oceanic plates. All the plates float atop the Earth's liquid mantle of molten magma. Due to convective forces, the plates move over the mantle like boxes on a conveyor belt. This movement causes them to interact in a number of ways.
Divergent Boundaries
- The first way plates interact is called a divergent boundary. Here, plates are forced apart. The gap is quickly filled by rising magma that solidifies, forming new crust. When oceanic plates diverge, the result is mid-ocean ridges. For example, the Mid-Atlantic Ridge is the result of the North American and Eurasian Plates spreading apart. When continental plates diverge, the result is a rift valley. The East African Rift is an example of continental divergence. Divergent zones are characterized by fluid basaltic lava flows.
Convergent Boundaries
- The second way plates interact is called a convergent boundary. Here, plates collide. This forces the denser plate to plunge under the more buoyant plate. Oceanic plates always subduct under continental plates. When two oceanic plates collide, the older and denser plate subducts under the younger and warmer plate. This process produces uplift of the overriding plate, an arc of volcanic activity and the formation of a deep trench. These subduction zones are where crust is destroyed, conserving the Earth's overall surface area. However, when two continental plates collide, neither subducts. Instead, they crush together under tremendous pressure, producing massive mountain ranges such as the Himalayas.
Transform Boundaries
- The last way plates interact is called a transform boundary. Here, plates slide horizontally past each other. This process creates a fault line. This most commonly occurs in the oceans, where they are called fracture zones. These faults and fractures usually connect two divergent boundaries. The San Andreas Fault is an example of a transform boundary that occurs on land. It represents the boundary between the Pacific Plate, which is moving toward the northwest, and the North American Plate, which is moving toward the southeast. The Clarion, Molokai and Pioneer fracture zones are examples of a transform boundary in the ocean.

Nature