Summary

These notes provide an overview of plate boundaries, including convergent, divergent, and transform boundaries, along with the causes of plate movement, such as convection currents. The document also explains ridge push and slab pull.

Full Transcript

Plate Boundaries Theory of Plate Tectonics Tectonic plates are huge pieces of crust and rigid upper mantle that fit together at their edges to cover Earth’s surface. Tectonic plates move in different directions and at different rates relative to one another and they interact with one...

Plate Boundaries Theory of Plate Tectonics Tectonic plates are huge pieces of crust and rigid upper mantle that fit together at their edges to cover Earth’s surface. Tectonic plates move in different directions and at different rates relative to one another and they interact with one another at their boundaries. Each type of boundary has certain geologic features and processes associated with it. Convergent Boundaries At convergent boundaries, two tectonic plates are moving toward each other. When two plates collide, the denser plate eventually descends below the other, less-dense plate in a process called subduction. 1. Oceanic-oceanic convergent boundary A subduction zone is formed when one oceanic plate, which is denser as a result of cooling, descends below another oceanic plate. The process of subduction creates an ocean trench and arc of volcanic islands that parallel the trench. 2. Oceanic-continental Convergent When the much denser oceanic plate converges with a continental plate, the oceanic plate is subducted. Oceanic-continental convergence produces a trench and volcanic arc. The result is a mountain range with many volcanoes. 3. Continental-continental boundaries Form when two continental plates collide, long after an oceanic plate has converged with a continental plate. This forms a vast mountain range, such as the Himalayas. Divergent Boundaries Divergent boundaries are regions where two tectonic plates are moving apart. Some divergent boundaries form on continents. When continental crust begins to separate, the stretched crust forms a long, narrow depression called a rift valley. Transform Boundaries A Transform boundary is a region where two plates slide horizontally past each other. Transform boundaries are characterized by long faults, sometimes hundreds of kilometers in length, and by shallow earthquakes. Causes of Plate Movement Convection Currents Convection is the transfer of thermal energy by the movement of heated material from one place to another. The cooling of matter causes it to contract slightly and increase in density. The cooled matter then sinks as a result of gravity. Warmed matter is forced to rise. This up-and-down flow produces a pattern of motion called a convection current. Convection currents develop in the mantle, moving the crust and outermost part of the mantle and transferring thermal energy from Earth’s interior to its exterior. Ridge Push and Pull Ridge push is the tectonic process associated with convection currents in Earth’s mantle that occurs when the weight of an elevated ridge pushes an oceanic plate toward a subduction zone. In slab pull, the weight of the relatively cool, dense subducting plate pulls the trailing slab into the subduction zone.

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