2ObjectivesDescribe how Earth’s tectonic plates result in many geologic features.Compare and contrast the three types of plate boundaries and the features associated with each.Generalize the processes associated with subduction zones.
3Key ConceptVolcanoes, mountains, and deep-sea trenches form at the boundaries between the plates.
5The 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.
6The Theory of Plate Tectonics Plate tectonics is the theory that describes how tectonic plates move and shape Earth’s surface.They move in different directions and at different rates relative to one another.They interact with one another at their boundaries.
7Divergent BoundariesRegions where two tectonic plates are moving apart are called divergent boundaries.Most divergent boundaries are found along the seafloor in rift valleys.The formation of new ocean crust at most divergent boundaries accounts for;high heat flowVolcanismearthquakesassociated with these boundaries.
8Divergent BoundariesSome divergent boundaries form on continents. When continental crust begins to separate, the stretched crust forms a long, narrow depression called a rift valley.
9Convergent 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.
11Convergent Boundaries There are three types of convergent boundaries, classified according to the type of crust involved. The differences in density of the crustal material affect how they converge.Oceanic-oceanic convergent boundaryOceanic-continental convergent boundaryContinental-Continental convergent boundary
12Oceanic-Oceanic Convergent Boundary In the 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.
13Oceanic-Oceanic Convergent Boundary In an oceanic-oceanic convergent boundary,water carried into Earth by the subducting platelowers the melting temperature of the plate,causing it to melt at shallower depths.The molten material is less dense so it rises back to the surface,where it often erupts and forms an arc of volcanic islands that parallel the trench.
14Oceanic-Continental Convergent Boundary When an oceanic plate converges with a continental plate, the denser oceanic plate is subducted. Oceanic- continental convergence producesa trenchvolcanic arcThe result is a mountain range with many volcanoes.
15Continental-Continental Convergent Boundary 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.
16Transform BoundariesA region where two plates slide horizontally past each other is a transform boundary.
17Transform BoundariesTransform boundaries are characterized by long faults, sometimes hundreds of kilometers in length, and by shallow earthquakes.Most transform boundaries offset sections of ocean ridges. Sometimes transform boundaries occur on continents.One of the best know examples of a transform boundary is the San Andreas Fault.
18Summary – Convergent Boundaries Boundary TypeCharacteristic FeaturesExamplesContinental-continental Convergent BoundaryFolded MountainsHimalayas (including Mt. Everest)Oceanic-oceanic Convergent BoundarySubduction ZoneForms Ocean TrenchForms Arc of Volcanic IslandsAleutian Trench and Aleutian Islands (N. Pacific)Marinas Trench and Marinas Islands (W. Pacific)Oceanic-continental Convergent BoundarySubduction Zone (Oceanic Plate Subducted)Forms Arc of Volcanic Mountains on ContinentPeru-Chile Trench and Andes Mountains
19Summary – Transform Boundaries Boundary TypeCharacteristic FeaturesExamplesTransform BoundaryPlates slide horizontally past each otherLong FaultsCrust Deformed or Fractured HereMost Found in Ocean RidgesCan be found on Continental CrustMovement causes EarthquakesSan Andreas FaultGibbs Fracture Zone (in Mid-Atlantic Ridge)
20Summary – Divergent Boundaries Boundary TypeCharacteristic FeaturesExamplesDivergent BoundaryMost Found on Seafloor in Rift ValleysHere is Where Seafloor Spreading StartsHigh Heat FlowVolcanismEarthquakesRift Valleys on Continental Crust can Lead to a New Ocean Basin.Mid-Atlantic RidgeRift Valley in Eastern Africa