![]() When oceanic crust collides with oceanic crust, both subduct to form an oceanic trench (e.g., Marianas trench). In zones of convergence, compressional forces (i.e., compression of lithospheric plate material) dominates. Lithospheric plates move on top of the asthenosphere (the outer plastically deforming region of Earth's mantle).Īt convergent boundaries, lithospheric plates move together in collision zones where crust is either destroyed by subduction or uplifted to form mountain chains. Lithospheric plates may contain various combinations of oceanic and continental crust in mutually exclusive sections (i.e., the outermost layer is either continental or oceanic crust, but not both except at convergent boundaries where subducting oceanic crust can make material contributions of lighter crustal materials to the overriding continental crust). Containing both crust and the upper region of the mantle, lithospheric plates are approximately 60 miles (approximately 100 km) thick. Continental crust is composed of lower density rocks such as granite and andesite. Continental crust comprises the outer layer of the lithospheric plates containing the existing continents and some undersea features near the continents. Oceanic crust is composed of high-density rocks, such as olivine and basalt. Oceanic crust comprises the outer layer of the lithosphere lying beneath the oceans. Each lithospheric plate is composed of a layer of oceanic crust or continental crust superficial to an outer layer of the mantle. Continental crust, composed of lighter, less dense materials, is too light to undergo subduction and so overrides oceanic crust or uplifts.Įarth's crust is fractured into approximately 20 lithospheric plates. Oceanic crust is denser than continental crust and is subductable. In addition, the buoyancy properties of the colliding lithospheric plates determine the outcome of the particular collision. Accordingly, at collision, each lithospheric plate carries tremendous momentum (the mathematical product of velocity and mass) that provides the energy to cause subduction or uplifting. Although lithospheric plates move very slowly (low velocities of inches per each), the plates have tremendous mass. This causes earthquakes.In terms of plate tectonics, collision boundaries are sites where lithospheric plates move together and the resulting compression causes either subduction (where one or both lithospheric plates are driven down and destroyed in the molten mantle) or crustal uplifting that results in orogeny (mountain building).Ĭolliding plates create tremendous force. As a result, when the two plates finally succeed in moving with respect to one another, huge amounts of energy are released. Lest you imagine a slippery, sliding motion, take note that the surfaces involved are exposed to huge amounts of stress and strain and are momentarily held in place. Transform boundaries are those that slide alongside one another. Another extreme formation due to the convergent boundary is the Mariana Trench, the deepest region on Earth. They formed when the Indian plate got subducted underneath the Eurasian plate. ![]() Convergent boundaries are responsible for producing the deepest and tallest structures on Earth.Īmong those that have formed due to convergent plate boundaries are K2 and Mount Everest, the tallest peaks in the world. Sometimes, the plate boundaries also experience buckling. That is, the denser plate gets subducted or goes underneath the less dense one. When they collide, subduction usually takes place. Convergent boundaries are those that move towards one another.
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