The Theory of Plate The Theory of Plate TectonicsTectonics

Background InformationBackground Information

The lithosphere (Earth’s Crust and Upper The lithosphere (Earth’s Crust and Upper Mantle) is made of plates. When magma Mantle) is made of plates. When magma rises from an ocean ridge (sea floor rises from an ocean ridge (sea floor spreading) the magma produces new crust, spreading) the magma produces new crust, which pushes plates apart.which pushes plates apart.

As these plates are pushed apart, other As these plates are pushed apart, other plates are pushed together.plates are pushed together.

Movement along any plate boundary Movement along any plate boundary results in changes at other boundaries. results in changes at other boundaries.

Major Plates of the Major Plates of the LithosphereLithosphere

Types of Plate BoundariesTypes of Plate Boundaries

Convergent Boundary – Convergent Boundary – plates plates move toward each other and collidemove toward each other and collide

Divergent Boundary – Divergent Boundary – plates move plates move away from each otheraway from each other

Transform Boundary - Transform Boundary - plates that plates that slide past one another. This causes slide past one another. This causes many of the features found on the many of the features found on the Earth. Earth.

Continental Drift – No MoreContinental Drift – No More

The theory of continental drift was no The theory of continental drift was no longer appropriate as scientists longer appropriate as scientists discovered how plates were moving discovered how plates were moving do a new name was given.do a new name was given. Theory of Plate TectonicsTheory of Plate Tectonics – proposes – proposes

that the plates of Earth’s lithosphere that the plates of Earth’s lithosphere interact with each other. interact with each other.

TectonicsTectonics – is the study of the – is the study of the movement of large-scale structural movement of large-scale structural features of Earth’s crust.features of Earth’s crust.

Convergent BoundariesConvergent Boundaries

are areas where the plates meet and are areas where the plates meet and collide. Earth’s crust is subducted collide. Earth’s crust is subducted into the mantle at these boundaries. into the mantle at these boundaries. ie India converged into the Eurasian ie India converged into the Eurasian plate and formed the Himalayas. plate and formed the Himalayas.

The area where a plate thrusts The area where a plate thrusts downward under another is known as downward under another is known as a a subduction zone. subduction zone.

3 Types of Convergent 3 Types of Convergent BoundariesBoundaries

1. Oceanic-Continental Convergence – When an 1. Oceanic-Continental Convergence – When an oceanic plate converges with a continental plate, oceanic plate converges with a continental plate, the oceanic plate sinks under the continental the oceanic plate sinks under the continental plate. Subduction zones along an oceanic-plate. Subduction zones along an oceanic-continental boundary create a deep-sea continental boundary create a deep-sea trenchtrench – – a long, narrow, deep depression in the sea floor. a long, narrow, deep depression in the sea floor.

Many of the trenches occur around the margin of Many of the trenches occur around the margin of the Pacific Ocean because of subduction. High the Pacific Ocean because of subduction. High temperatures cause rock to melt around the temperatures cause rock to melt around the oceanic plate as it goes under the continental oceanic plate as it goes under the continental plate. The newly formed magma is forced upward plate. The newly formed magma is forced upward through the upper plate, forming volcanoes. through the upper plate, forming volcanoes.

3 Types of Convergent 3 Types of Convergent BoundariesBoundaries

2. Oceanic-Oceanic Convergence – when 2. Oceanic-Oceanic Convergence – when an oceanic plate meets another oceanic an oceanic plate meets another oceanic plate, the older, colder, denser plate bends plate, the older, colder, denser plate bends and sinks into the mantle. New crust is and sinks into the mantle. New crust is then formed as the magma rises to make then formed as the magma rises to make volcanoes. Oceanic-oceanic convergence volcanoes. Oceanic-oceanic convergence also makes deep sea trenches. The island also makes deep sea trenches. The island of Japan and the Japan Trench were of Japan and the Japan Trench were formed by oceanic plates converging.formed by oceanic plates converging.

3 Types of Convergent 3 Types of Convergent BoundariesBoundaries

3. Continental-Continental Convergence 3. Continental-Continental Convergence – When two plates of continental crust – When two plates of continental crust collide and crumple up, tall mountain collide and crumple up, tall mountain ranges may form. Earthquakes are ranges may form. Earthquakes are common at these convergent common at these convergent boundaries. Volcanoes do not form, boundaries. Volcanoes do not form, however, because there is little or no however, because there is little or no subduction when two continental plates subduction when two continental plates collide. collide.

Convergent BoundaryConvergent Boundary

Divergent BoundariesDivergent Boundaries

Occurs when plates move away from Occurs when plates move away from each other. Sea floor spreading each other. Sea floor spreading occurs along a divergent boundary. occurs along a divergent boundary. The Mid-Atlantic Ridge in the Atlantic The Mid-Atlantic Ridge in the Atlantic Ocean is an example of a divergent Ocean is an example of a divergent boundary.boundary.

Divergent BoundaryDivergent Boundary

Transform BoundaryTransform Boundary

Transform boundaries occur where Transform boundaries occur where two plates slide past one another. two plates slide past one another. The plates move in opposite The plates move in opposite directions or in the same direction at directions or in the same direction at different rates. When one plate slips different rates. When one plate slips past another plate suddenly, an past another plate suddenly, an earthquake occurs. earthquake occurs.

Transform BoundaryTransform Boundary

How do we measure Plate How do we measure Plate Movement?Movement?

Earthquakes, volcanoes and mountain ranges are Earthquakes, volcanoes and mountain ranges are evidence of plate movement. evidence of plate movement.

The theory of plate tectonics suggests that The theory of plate tectonics suggests that convection currents inside Earth can affect the crust convection currents inside Earth can affect the crust differently in different locations. You have seen how differently in different locations. You have seen how the plates have moved since Pangaea separated. the plates have moved since Pangaea separated.

Scientists now use satellites and laser technology to Scientists now use satellites and laser technology to measure the exact movements of the plates, to the measure the exact movements of the plates, to the nearest centimeter. Laser pulses are shot from the nearest centimeter. Laser pulses are shot from the ground to a satellite to determine an exact location ground to a satellite to determine an exact location on the ground. New data confirm that parts of the on the ground. New data confirm that parts of the crust are moving from 1 – 12 centimeters each year. crust are moving from 1 – 12 centimeters each year.

Scientists are also using GPS by repeatedly Scientists are also using GPS by repeatedly measuring distances between specific points.measuring distances between specific points.