leftem.blogg.se - Continental continental convergent boundary

On the overriding plate, a volcanic island arc (a chain of off-shore volcanoes) forms parallel to the trench. Oceanic-oceanic convergent boundary: Converging oceanic plates form trenches in the subduction zone, the point where the denser plate is subducted. While the motion of the plates is the same, the resulting landforms can be very different depending on the type of plates involved. Convergent BoundaryĬonvergent boundaries occur when two plates move towards each other (converge).

At each boundary, the resulting landforms depend on whether the plates involved are oceanic, continental, or both types.įigure 1: The three categories of plate boundaries: convergent, divergent, and transform. In this region, the continental crust on both sides of the plate boundary are too light to sink into the mantle.There are three categories of plate boundaries: convergent, divergent, and transform. Migration of "India" away from ancient Pangaea has led to the collision of continental land masses resulting in the rise of the Himalayan Mountains. Appalachians Mountains in the eastern United States (formed when North America collided with Africa about 350-400 million years ago (before the Atlantic Ocean opened later).įigure 4.18.Alps Mountains are being pushed up by collisions between Africa (and Italian Peninsula) with Europe.Himalayas (India) beginning 45 million years ago) (Figure 4.18).Mountain building occurs with lots of earthquakes massive erosion also occurs.This is where you form the very large mountain chains.Both are very buoyant and want to "float" or ride high.When continents collide with other continental landmasses: Subduction zones associated with ocean trenches surround much of the Pacific Ocean Basin.Ĭ) Continental Collisions: continental crust (CC) colliding with continental crust (CC) Subduction zones are where oceanic crust is destroyed and new continental crust forms. Subduction zone geometry (OC/CC) is revealed by the location of earthquakes and volcanic activity. Rainier, Mount Shasta, Crater Lake and many others) Figure 4.15. Cascades in United States (include such volcanoes as Mt.Rates of subduction are up to 15 cm/yr in the active margins of the Pacific Basin.Subduction reduces amount of (and destroys) OC.Trenches are especially well developed in regions far away from spreading centers (where the ocean crust is old, cold, and denser, and therefore sinks more rapidly).

Deep trenches form around continents margins.

Examples include the Andes and the Cascade Range, etc.

Volcanoes of the andesite (explosive) type.

Subduction produces both deep and shallow focus earthquakes (with tsunami potential) the largest ever-9.5 magnitude in Peru/Chile Trench in 1960.

A chain of volcanoes formed, called a continental volcanic arc.

Denser, thinner OC is pushed or subducted beneath less dense and more buoyant CC.

Earthquake data reveals the geometry of a subduction zone in the region of Tonga.Ī) Subduction of ocean crust (OC) beneath continental crust (CC). The earthquake data suggests that the eastern edge of the Australian Plate is being over run by the western edge of the Pacific Plate, and that rocks of the Australian Plate are descending into the upper mantle.įigure 4.14. Earthquake data shows that a major fault system descends at an angle, extending eastward beneath the Tonga Island and extends of hundreds of kilometers at a steep angle deep into the upper mantle (asthenosphere) where it is presumed that earthquakes cease because rocks are too hot and under intense pressure that it easier for them to fold and flow plastically than to fracture as brittle rock. A deep ocean trench runs along the southeast side of the island chain. This diagram show the location and intensity of earthquakes over a period of time in the vicinity of the Tonga Islands in the South Pacific Ocean. Most tsunamis are generated by subduction-zone-related earthquakes.įigure 4.14 illustrates how earthquake data reveals the geometry of a subduction zone. An example is the Cascadia Subduction Zone offshore of Washington, Oregon, and northern California (see Figure 4.19 below). A subduction zone is usually marked by a deep trench on the sea floor. They are associated with active margins-locations where mountain building is occurring, resulting in numerous earthquakes and andesite (explosive) volcanoes.Ī subduction zone is a plate boundary along which one plate of the Earth’s outer shell descends (subducts) at an angle beneath another (Figure 4.14). \)Ĭonvergent Plates move together and collide so you have compressional forces.